Taking and Importing Marine Mammals; Taking Marine Mammals Incidental to Construction and Operation of a Liquefied Natural Gas Deepwater Port in the Gulf of Mexico
Proposed Rule; Request For Comments.
NMFS has received a request from Port Dolphin Energy LLC (Port Dolphin) for authorization to take marine mammals incidental to port construction and operations at its Port Dolphin Deepwater Port in the Gulf of Mexico, over the course of five years; approximately June 2013 through May 2018. Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is proposing regulations to govern that take and requests information, suggestions, and comments on these proposed regulations.
Taking and Importing Marine Mammals; Taking Marine Mammals Incidental to Construction and Operation of a Liquefied Natural Gas Deepwater Port in the Gulf of Mexico
3 actions from March 1st, 2011 to December 2011
March 1st, 2011
March 31st, 2011
- ANPRM Comment Period End
Table of Contents Back to Top
- FOR FURTHER INFORMATION CONTACT:
- SUPPLEMENTARY INFORMATION:
- Summary of Request
- Description of the Specified Activity
- Region of Activity
- Dates of Activity
- LNG and SRVs
- Port Construction
- Port Operations
- Method of Incidental Taking
- Description of Sound Sources
- Sound Attenuation Devices
- Sound Thresholds
- Distance to Sound Thresholds
- Comments and Responses
- Background on Marine Mammal Hearing
- Potential Effects of the Specified Activity on Marine Mammals
- Hearing Impairment and Other Physiological Effects
- Anticipated Effects on Habitat
- Seafloor Disturbance
- Seawater Intake and Discharge
- Sound Disturbance
- Proposed Mitigation
- Monitoring and Shutdown
- Monitoring Protocols
- Pile Driving
- Vessel Strike Avoidance
- Best Management Practices
- Benthic Habitat
- Proposed Monitoring and Reporting
- Acoustic Monitoring
- Visual Monitoring
- Proposed Reporting
- Adaptive Management
- Estimated Take by Incidental Harassment
- Negligible Impact and Small Numbers Analysis and Preliminary Determination
- Impact on Availability of Affected Species or Stock for Taking for Subsistence Uses
- Endangered Species Act (ESA)
- National Environmental Policy Act (NEPA)
- Information Solicited
- List of Subjects in 50 CFR Part 217
- PART 217—REGULATIONS GOVERNING THE TAKE OF MARINE MAMMALS INCIDENTAL TO SPECIFIED ACTIVITIES
- Subpart P—Taking Marine Mammals Incidental to Construction and Operation of a Liquefied Natural Gas Deepwater Port in the Gulf of Mexico
- Subpart P—Taking Marine Mammals Incidental to Construction and Operation of a Liquefied Natural Gas Deepwater Port in the Gulf of Mexico
Tables Back to Top
- Table 1—Vessels To Be Employed During Port Dolphin Construction and/or Facility Installation Operations
- Table 2—SRV Speeds and Thruster Use During Transit, Approach, and Maneuvering/Docking Operations at the DWP
- Table 3—Projected Construction, Installation, and Operations Activities, by Season
- Table 4—Underwater SPLs for Representative Vessels
- Table 5—Anticipated Source Levels for Construction/Installation and Operations at the Port Dolphin DWP
- Table 6—Representative Scenarios Modeled During the Port Dolphin Sound Source Analysis and Radial Distance to Thresholds
- Table 7—Marine Mammals in the Gulf of Mexico
- Table 8—Density Estimates for Marine Mammals in the Nearshore and Mid-Shelf Depth Strata, Eastern GOM
- Table 9—Estimated Incidental Take, Construction Activities
- Table 10—Estimated Yearly Incidental Take, Port Operations
DATES: Back to Top
Comments and information must be received no later than October 25, 2012.
ADDRESSES: Back to Top
You may submit comments on this document, identified by FDMS Docket Number 110801452-2387-03, by any of the following methods:
- Electronic Submission: Submit all electronic public comments via the Federal e-Rulemaking Portal www.regulations.gov. To submit comments via the e-Rulemaking Portal, first click the Submit a Comment icon, and then enter 110801452-2387-03 in the keyword search. Locate the document you wish to comment on from the resulting list and click on the Submit a Comment icon on the right of that line.
- Hand delivery or mailing of comments via paper or disc should be addressed to Michael Payne, Chief, Permits and Conservation Division, Office of Protected Resources, National Marine Fisheries Service, 1315 East-West Highway, Silver Spring, MD 20910.
Comments regarding any aspect of the collection of information requirement contained in this proposed rule should be sent to NMFS via one of the means provided here and to the Office of Information and Regulatory Affairs, NEOB-10202, Office of Management and Budget, Attn: Desk Office, Washington, DC 20503, OIRA@omb.eop.gov.
Instructions: Comments must be submitted by one of the above methods to ensure that the comments are received, documented, and considered by NMFS. Comments sent by any other method, to any other address or individual, or received after the end of the comment period, may not be considered. All comments received are a part of the public record and will generally be posted for public viewing on www.regulations.gov without change. All personal identifying information (e.g., name, address) submitted voluntarily by the sender will be publicly accessible. Do not submit confidential business information, or otherwise sensitive or protected information. NMFS will accept anonymous comments (enter N/A in the required fields if you wish to remain anonymous). Attachments to electronic comments will be accepted in Microsoft Word, Excel, or Adobe PDF file formats only.
FOR FURTHER INFORMATION CONTACT: Back to Top
Ben Laws, Office of Protected Resources, NMFS, (301) 427-8401.
SUPPLEMENTARY INFORMATION: Back to Top
Availability Back to Top
A copy of Port Dolphin's application may be obtained by writing to the address specified above (see ADDRESSES), calling the contact listed above (see FOR FURTHER INFORMATION CONTACT), or visiting the Internet at: http://www.nmfs.noaa.gov/pr/permits/incidental.htm. To help NMFS process and review comments more efficiently, please use only one method to submit comments.
Background Back to Top
Sections 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361 et seq.) direct the Secretary of Commerce to allow, upon request, the incidental, but not intentional, taking of small numbers of marine mammals by U.S. citizens who engage in a specified activity (other than commercial fishing) within a specified geographical region if certain findings are made and either regulations are issued or, if the taking is limited to harassment, a notice of a proposed authorization is provided to the public for review.
Authorization for incidental takings shall be granted if NMFS finds that the taking will have a negligible impact on the species or stock(s), will not have an unmitigable adverse impact on the availability of the species or stock(s) for subsistence uses (where relevant), and if the permissible methods of taking and requirements pertaining to the mitigation, monitoring and reporting of such takings are set forth. NMFS has defined “negligible impact” in 50 CFR 216.103 as “* * * an impact resulting from the specified activity that cannot be reasonably expected to, and is not reasonably likely to, adversely affect the species or stock through effects on annual rates of recruitment or survival.”
Except with respect to certain activities not pertinent here, the MMPA defines “harassment” as: “any act of pursuit, torment, or annoyance which (i) has the potential to injure a marine mammal or marine mammal stock in the wild [`Level A harassment']; or (ii) has the potential to disturb a marine mammal or marine mammal stock in the wild by causing disruption of behavioral patterns, including, but not limited to, migration, breathing, nursing, breeding, feeding, or sheltering [`Level B harassment'].”
Summary of Request Back to Top
On February 1, 2011, NMFS received a complete application from Port Dolphin for the taking of marine mammals incidental to port construction and operations at its Port Dolphin Deepwater Port (DWP) facility in the Gulf of Mexico (GOM). During the period of these proposed regulations (June 2013-May 2018), Port Dolphin proposes to construct the DWP and related infrastructure—expected to occur over an approximately 11-month period, beginning in June 2013—and to subsequently begin operations. The proposed DWP, which is designed to have an operational life expectancy of 25 years, would be an offshore liquefied natural gas (LNG) facility, located in the GOM approximately 45 km (28 mi) off the western coast of Florida, and approximately 68 km (42 mi) from Port Manatee, located in Manatee County, Florida, within Tampa Bay (see Figure S-1 in Port Dolphin's application). The DWP would be in waters of the U.S. Exclusive Economic Zone (EEZ) approximately 31 m (100 ft) in depth. The proposed DWP would consist principally of a permanently moored buoy system, designed for offloading of natural gas, leading to a single proposed new natural gas transmission pipeline that would come ashore at Port Manatee and connect to existing infrastructure.
Take of marine mammals would occur as a result of the introduction of sound into the marine environment during construction of the DWP and pipeline and during DWP operations, which would involve shuttle regasification vessel (SRV) maneuvering, docking, and debarkation, as well as regasification activity. Because the specified activities have the potential to take marine mammals present within the action area, Port Dolphin requests authorization to incidentally take, by Level B harassment only, small numbers of bottlenose dolphin (Tursiops truncatus) and Atlantic spotted dolphin (Stenella frontalis).
Description of the Specified Activity Back to Top
Port Dolphin proposes to own, construct, and operate a DWP in the U.S. EEZ of the GOM Outer Continental Shelf (OCS) approximately 45 km (28 mi) off the western coast of Florida to the southwest of Tampa Bay, in a water depth of approximately 31 m (100 ft). On March 29, 2007, Port Dolphin submitted an application to the U.S. Coast Guard (USCG) and the U.S. Maritime Administration (MarAd) for all federal authorizations required for a DWP license under the Deepwater Port Act of 1974 (DWPA). Port Dolphin received that license in October 2009. The Port would consist of a permanently moored unloading buoy system with two submersible buoys separated by a distance of approximately 5 km (3 mi). The buoys would be designed to moor a specialized type of LNG carrier vessel (i.e., SRVs) and would remain submerged when vessels are not present. Regasified natural gas would be sent out through the unloading buoy to a 36-in (0.9 m) pipeline that would connect onshore at Port Manatee with the existing Gulfstream Natural Gas System and Tampa Electric Company (TECO) Bayside pipeline. The DWP would only serve SRVs. Construction of the DWP would be expected to take 11 months. Port Dolphin DWP would be designed, constructed, and operated in accordance with applicable codes and standards and would have an expected operating life of approximately 25 years. The locations of the DWP and associated pipeline are shown in Figure S-1 in Port Dolphin's application; Figure 1-1 of the same document depicts a conceptual site plan for the DWP.
The installation of the DWP facilities would include the construction and installation of offshore buoys, mooring lines, and anchors. The two unloading buoys, also known as submerged turret loading (STL) buoys, would each have eight mooring lines connected to anchor points, likely consisting of piles driven into the seabed. When not connected to a SRV, STL buoys would be submerged 60 to 70 ft (18 to 21 m) below the sea surface. The installation of the pipeline from the DWP to shore would include burial of the pipeline, selective placement of protective cover (either rock armoring or concrete mattresses) over the pipeline at several locations along the pipeline route where full burial is not possible, and the horizontal directional drilling (HDD) of three segments of the pipeline.
SRVs are specialized LNG carriers designed to regasify the LNG prior to off-loading for transport to shore. Each STL buoy would moor one SRV on location throughout the unloading cycle. An SRV would typically moor at the deepwater port for between 4 and 8 days, depending on vessel size and send-out rate. Unloading of natural gas (i.e., vaporization or regasification) would occur through a flexible riser connected to the STL buoy and into the pipeline end manifold (PLEM) for transportation to shore via the subsea pipeline. With two separate STL buoys, Port Dolphin may schedule an overlap between arriving and departing SRVs, thus allowing natural gas to be delivered in a continuous flow.
Port Dolphin is planning for an initial natural gas throughput of 400 million standard cubic feet per day (MMscfd). Although the Port would be capable of an average of 800 MMscfd with a peak capacity of 1,200 MMscfd, this level of throughput would not be achieved during the span of this proposed rule. Based on a regasification cycle of approximately 8 days and initial throughput of 400 MMscfd, maximum vessel traffic during operations over the lifetime of the proposed 5-year regulations is projected to consist of 46 SRV unloadings per year.
In the open ocean, SRVs typically travel at speeds of up to 19.5 kn (36.1 km/hr). When approaching the vicinity of the DWP (i.e., during approach to the DWP), the SRVs would typically slow to about half speed. In close proximity to the STL buoys, the SRVs would slow to dead slow and utilize thrusters to attain proper vessel orientation relative to the DWP, taking into consideration ambient ocean currents, wind conditions, and buoy position. The following subsections describe the Region of Activity and the preceding facets of construction and operation in greater detail.
Region of Activity
The GOM is a marine water body bounded by Cuba on the southeast; Mexico on the south and southwest; and the U.S. Gulf Coast on the west, north, and east. The GOM has a total area of 564,000 km  (217,762 mi  ). Shallow and intertidal areas (water depths of less than 20 m) compose 38 percent of the total area, with continental shelf (22 percent), continental slope(20 percent), and abyssal plain (20 percent) composing the remainder of the basin. The project site is located on the west Florida Shelf, a portion of the Inner Continental Shelf, in an area of relatively low wave energy and tidal variation (Gore, 1992).
The GOM is separated from the Caribbean Sea and Atlantic Ocean by Cuba and other islands, and has relatively narrow connections to the Caribbean and Atlantic through the Florida and Yucatan Straits. The GOM is composed of three distinct water masses, including the North and South Atlantic Surface Water (less than 100 m deep), Atlantic and Caribbean Subtropical Water (up to 500 m deep), and Subantarctic Intermediate Water.
Circulation within the GOM, and within the project area, is dominated by the Loop Current, which enters the GOM flowing north through the Yucatan Strait, flows south along the Florida coast in the vicinity of the project area, and exits the GOM through the Florida Straits. The velocity of the current in the project area ranges between 1.56 and 15.16 cm/s in summer, and 1.79 to 25.36 cm/s in winter (APL, 2006). The direction of flow in the project area is generally south to southeast.
In shallow areas along the west Florida Shelf, additional influences on water flow and circulation include wind stress, freshwater inflow, and variations in buoyancy (Gore, 1992). Wind speeds at the project site range from 2.26 to 7.61 m/s in summer, and 2.85 to 11.04 m/s in winter (APL, 2006). Tidal variation along Florida's west-central continental shelf is moderate, with an average range of approximately 2 ft (0.6 m) (Gore, 1992).
At the eastern edge of the Loop Current along the west Florida Shelf, circulation patterns result in an upwelling of deep nutrient-rich water. This upwelling supports a high level of biological activity, producing large concentrations of plankton. Nutrient levels (primarily nitrogen and phosphorus) are also affected by runoff from agricultural and urbanized areas and from submarine groundwater discharge, leading to red tide conditions. In the project area, red tide occurs on an almost annual basis (Hu et al., 2006). Red tides are caused by rapid growth of the species Karenia brevis, a toxic species which produces brevetoxins (a type of neurotoxin) that can accumulate in bivalves and cause mortality in marine organisms (Hu et al., 2006). The rapid growth of these organisms can also create a hypoxic zone (area with dissolved oxygen concentrations below 2 mg/L), which can cause mortality among benthic communities, fish, turtles, birds, and marine mammals (Hu et al., 2006).
Extreme variations in water circulation patterns, tides, and wave heights can occur along the west Florida coast during periodic tropical storms and hurricanes. Warm water within the Loop Current can act as an energy source in summer and fall months, fueling the development of these storms. Features of these storms that can affect natural circulation and topography include high winds, flooding, storm surges, and beach erosion.
Tampa Bay is an estuary formed by the rise of sea level into a former river valley. Tampa Bay consists of four subregions, including lower Tampa Bay, middle Tampa Bay, Old Tampa Bay, and Hillsborough Bay. The project area would only extend to Port Manatee, within Lower Tampa Bay, near the outlet of the bay into the GOM. The bay covers an area of 1,030 km  within Hillsborough, Manatee, and Pinellas counties. Freshwater inflow to the bay occurs through four major river systems (Alafia, Hillsborough, Little Manatee, and Manatee), as well as more than a hundred minor creeks and rivers.
Water circulation within the bay is driven by freshwater inflow, tides, and winds. The bay has an average depth of 3.5 to 4 m. There is well-developed horizontal stratification in the bay, with fresh water flowing along the surface out to sea, and denser saline water flowing into the bay along the bottom.
The Tampa Bay area has a population of more than two million people, and tributaries, habitat, runoff patterns, and water quality are all affected by urbanization. Specific actions that have affected the bay include removal of mangroves, dumping of sewage, artificial filling, and modification of runoff from paved surfaces (Peene et al., 1992).
Dates of Activity
Port Dolphin has requested regulations governing the incidental take of marine mammals for the five-year period from June 2013 through May 2018. Construction and installation of the port and pipeline would last approximately 11 months, with subsequent operations (i.e., SRV docking and regasification) occurring for the remainder of the specified time period.
LNG and SRVs
The DWPA establishes a licensing system for ownership, construction, and operation of deepwater ports in waters beyond the territorial limits of the United States. Originally, the DWPA promoted the construction and operation of deepwater ports as a safe and effective means of importing oil into the United States and transporting oil from the OCS, while minimizing tanker traffic and associated risks close to shore. The Maritime Transportation Security Act of 2002 amended the definition of “deepwater port” to include facilities for the importation of natural gas.
LNG is natural gas that has been cooled to about −260 °F (−162 °C) for efficient shipment and storage as a liquid. LNG is more compact than the gaseous equivalent, with a volumetric differential of about 610 to 1. LNG can thus be transported long distances across oceans using specially designed ships (e.g., SRVs), allowing efficient access to stranded reserves of natural gas that cannot be transported by conventional pipelines.
This proposed STL buoy system differs from other common LNG offload technologies insofar as it does not involve any permanent storage or regasification facility at the DWP, thus minimizing required infrastructure at the DWP itself. Rather, STL buoys receive SRVs that contain onboard LNG vaporization equipment. After mooring, LNG is vaporized onboard the vessel and discharged via the unloading buoy and a flexible riser into the subsea pipeline. Because the LNG is vaporized with the SRV's onboard equipment, no permanent fixed or floating storage or vaporization facilities are required. However, this means that the offload process can take 5 to 8 days, as compared with a standard offload of 18 hours or less. As a result of this trade-off, continuous off-loading operations are essential to minimize fluctuations in the throughput of natural gas. The SRVs proposed for use would be equipped to transport, store, vaporize, and meter natural gas. A closed-loop, glycol/water-brine heat transfer system would be used to vaporize the LNG. Closed-loop systems burn vaporized LNG in order to heat an intermediate fluid (e.g., glycol/water-brine), which warms the LNG. The closed-loop system results in reduced environmental impacts on water quality and marine resources; although these systems do require seawater for use in cooling electrical generating equipment (resulting in subsequent entrainment of fish eggs and plankton, as well as discharge of water at elevated temperatures), such usage is significantly reduced from that required in an open-loop system.
SRVs with approximate cargo capacities of either 145,000 m  or 217,000 m  (189,653-283,825 yd  ) based on standard designs for oceangoing LNG carriers would be used to supply LNG to the Port. Approximate dimensions of each SRV would range from 280 m (919 ft) in length and 43 m (141 ft) in breadth, with a design draft of 11.4 m (37.4 ft) for the smaller vessels to 315.5 m (1,035 ft) in length and 50 m (164 ft) in breadth, with a design draft of 12 m (39 ft) for the larger vessels. The maximum height above the waterline would be 41.1 m (135 ft). The 145,000 m  SRV would displace 80,000 t (88,185 ton) and the 217,000 m  SRV would displace 108,000 t (119,050 ton). The vessels would be equipped with a trunk and mating cone to receive the unloading buoy, lifting and connection devices, an LNG vaporization system, and gas metering systems. All critical functions would be manned 24 hours per day; other functions would be accomplished on a regular, scheduled basis.
The SRVs would have two thrusters forward and could have one or two thrusters aft. Thrusters allow precise control of positioning while mooring with the STL buoy. The dynamic positioning system would be used while retrieving the submerged unloading buoy handling line and moving onto the buoy. The system normally would not be used while the SRV is moored to the unloading buoy. SRVs would be equipped with an acoustic position reporting system that would monitor the buoy's draft and position before and during connection/disconnection; this would be enabled by six transponders located on the buoy itself.
Seawater would be used to ballast the SRV, cool the dual-fuel diesel engines supplying power for the regasification process, and condense the steam produced by the boilers supplying heat to the vaporization process. Ballasting the SRV is required to maintain proper buoyancy as the LNG is vaporized and offloaded through the pipeline. Water intake for ballasting the SRV would require an average intake of 360 m  per hour (2.3 MGD) over the vaporization cycle. The cooling water system would require an additional intake of approximately 1,520 m  per hour (9.5 MGD) and would take in seawater through one of two sea chests, each measuring 1.5 x 2.0 m (4.9 x 6.6 ft). Water velocity through the lattice screens at the hull side shell would not exceed 0.15 m/s (0.49 ft/s) at the maximum flow rate of 1,520 m  per hour.
Cooling water discharges would be made at points removed from the intake sea chests to avoid recirculating warmed water through the cooling system. All of the cooling water would be discharged at a temperature of approximately 10 °C (18 °F) above the ambient water temperature. Although the seawater system would be equipped with a chlorination system to prevent biofouling of heat transfer surfaces and system components, the chlorination system would not be used while the SRVs are approaching the Port or moored at the buoys.
In-water construction of Port Dolphin is expected to begin in June 2013 and last a total of approximately 11 months. Construction would include siting the STL buoys and associated equipment and laying the marine pipeline. Construction is assumed to be continuous from mobilization to demobilization with no work stoppages due to weather or other issues. Please see Table 2-1 of Port Dolphin's application for a graphical depiction of the complete timeline of proposed construction activities. Port Dolphin anticipates that construction/installation would be accomplished in the following sequence:
- Install the Port Manatee HDD section, with installation proceeding from onshore to the offshore location.
- Install the anchor piles and the mooring lines using the main installation vessel at the DWP.
- Construction and installation of the HDD pipe sections for the segments under the existing Gulfstream pipeline.
- Install seabed pipe segments between the Port Manatee HDD segment and the Gulfstream HDD segments.
- Install the Skyway Bridge section of the pipe (requiring dredging through the causeway).
- Install the STL Buoys.
- Install the two risers from the PLEMs.
- Install the north and south PLEMs.
- Perform pipelay and diving operations towards the Y-connector.
- Install the flowlines on the seafloor.
- Complete tie-ins and bury or armor the pipeline, as necessary.
- Conduct testing of the pipeline upon completion of burial operations.
These components of in-water construction are discussed in greater detail in the following subsections.
DWP Construction/Installation—As described previously, the Port would include two STL unloading buoy systems, separated by a distance of approximately 5 km (3.1 mi) in a water depth of approximately 31 m (100 ft). Each unloading buoy would have eight mooring lines, consisting of wire rope and chain, connecting to eight driven-pile anchor points on the sea floor, one 16-in (0.4-m) inside diameter flexible pipe riser, and one electrohydraulic control umbilical from the unloading buoy to the riser manifold. When not connected to a SRV, STL buoys would be submerged 60 to 70 ft (18 to 21 m) below the sea surface. A concrete or steel landing pad would be fixed to the sea floor by means of a skirted mud mat to allow lowering of the STL buoy to the ocean floor when it is not in use.
The mooring lines would be designed so that the SRV could remain moored in non-hurricane 100-year storm conditions, and would vary in length, from 1,800 to 4,000 ft (549 to 1,219 m) for the northern unloading buoy and from 2,500 to 3,600 ft (762 to 1,097 m) for the southern buoy. The mooring lines would consist of 132-mm (5.2-in) chain and 120-mm (4.7-in) spiral-strand wire rope. The riser system for each unloading buoy would consist of one 16-in interior diameter flexible riser in a steep-wave configuration. Total length of the riser would be approximately 82 m (269 ft). The riser would be directed between two of the mooring lines, and would lie on the seafloor when not in use.
The two PLEMs near the unloading buoys would connect the flexible risers to the flowlines and a Y-connection that would connect the two flowlines to the new gas transmission pipeline. Each of the two PLEMs would be approximately 75 m (246 ft) offset from the proposed unloading buoy locations. The purpose of a PLEM is to provide an interface between the pipeline system and the flexible riser, isolate the riser between gas unloading operations, and attach a subsea pig launcher or receiver as necessary. “Pigs,” or “pipeline inspection gauges,” travel remotely through a pipeline to conduct inspections of or clean the pipeline and collect data about conditions in the pipeline. Each PLEM would include a flange connection for attaching the flexible riser or the subsea pig launcher/receiver and a full-bore subsea hydraulic control valve and electrohydraulic umbilical termination assembly. Each PLEM would have a mud mat foundation to provide a stable base for bearing PLEM and riser weight and to resist sliding and overturning forces. Please see Figure 1-1 in Port Dolphin's application for a conceptual diagram of the DWP.
Offshore installation activities at the DWP would begin with installation of the PLEMs at both STL buoy locations (north and south), followed by placement of the buoy anchors, mooring lines, buoys, and risers. Installation activities at both STL buoy locations would require a cargo barge, supported by anchor-handling support vessels, a supply boat, a crew transfer boat, and a tug. Buoy anchors would likely be installed via impact pile driving.
Pipeline Installation—The pipeline would be laid on the seafloor by a pipelaying barge and then buried, typically using a plowing technique. Other techniques, such as dredging and HDD, are planned to be used in certain areas depending on the final geotechnical survey, engineering considerations, and equipment selection. At the western (seaward) end, the pipeline would consist of two 36-in (0.9-m) flowlines connected to the north and south PLEMs, which would connect at a Y-connection approximately 3.2 km (2 mi) away (see Figure 1-1 in Port Dolphin's application). From the Y-connection a 36-in (0.9-m) gas transmission line would travel approximately 74 km (46 mi) to interconnections with the Gulfstream and TECO pipeline systems. The pipelines would have a nominal outer diameter of 36 in, with a coating of fusion-bonded epoxy and a concrete weight coating thickness of 11.4 cm (4.5 in).
Pipeline trenching and burial requirements are governed by Department of the Interior regulations at 30 CFR 250 Subpart J, which requires pipelines and all related appurtenances to be protected by 3 ft (0.9 m) of cover for all portions in water depths less than 200 ft (61 m). Portions of the pipeline that travel through hard-bottom areas may not be able to be buried to the full 3 ft depth. In these areas, flexible concrete mattresses or other cover would be used to cover the pipeline. In places where the pipeline crosses shipping lanes, it would be buried 10 ft (3 m) deep if the sea floor permits plowing. Burying the pipeline and flowlines would protect them from potential damage from anchors and trawls and avoid potential fouling, loss, or damage of fishermen's trawls. The pipeline construction corridor would be 3,000 ft (914 m) wide in offshore areas. The permanent in-water right-of-way for the pipeline would be 200 ft (61 m) wide.
Under the plowing method, the pipeline is lowered below seabed level by shearing a V-shaped ditch underneath it. The plow is towed along and underneath the pipeline by the burial barge. As the ditch is cut, sediment is removed and passively pushed to the side by specially shaped moldboards that are fitted to the main plowshare. The trench is then backfilled with a subsequent pass of the plow. The estimated width of the trench (including sediments initially pushed to each side) is 67 ft (20.4 m) (see Figure 1-2 in Port Dolphin's application for a conceptual diagram of this process).
In areas that cannot be plowed (e.g., due to hard/live bottom) or complete burial cannot be achieved, the pipeline would be covered with an external cover (e.g., concrete mattresses or rock armoring). Although plowing is the preferred methodology for pipeline burial, other techniques such as dredging and HDD would be used where required. Figure 1-3 of Port Dolphin's application uses color coding of the proposed pipeline route to show where these various methodologies would be used, based on bottom structure and other barriers. The total length of the pipeline route is 74 km. Burial techniques to be used along the pipeline route and their relative lengths are characterized as follows:
- Plowing/trenching soft sediments: 39.6 km (24.6 mi; 53.2 percent of total pipeline length);
- Plowing/external cover: 23.3 km (14.5 mi; 31.4 percent);
- External cover (concrete mattress/rock armoring): 8.5 km (5.3 mi; 11.7 percent);
- Clamshell dredging/dragline burial: 0.3 km (0.2 mi; 0.5 percent); and
- HDD: 2.4 km (1.5 mi; 3.2 percent).
HDD would be employed for installation of the pipeline at three locations along the inshore portion of the route. The proposed HDD locations include drilling from land to water at the Port Manatee shore approach and from water-to-water at two crossings of the existing Gulfstream pipeline. The eastern HDD crossing would be 898 m (2,947 ft) in length, and the western HDD crossing would be 407 m (1,335 ft) in length. Both crossings would be in a water depth of 6.4 m (21 ft). The Port Dolphin pipeline would be drilled to a depth of approximately 6 m (20 ft) below the existing Gulfstream Pipeline (Port Dolphin, 2007b).
HDD is a steerable method of installing pipelines underground along a prescribed bore path, with minimal impact on the surrounding area. The process starts with location of entry and exit points. The first stage drills a pilot hole on the designed path, and the second stage enlarges the hole by passing a larger cutting tool known as a reamer. This would involve using progressively larger drill strings to eventually produce a drill bore 48 in (1.22 m) in diameter. The third stage places the product or casing pipe in the enlarged hole by way of the drill steel and is pulled behind the reamer to allow centering of the pipe in the newly reamed path. Simultaneously, bucket dredging would be employed to produce an exit hole at the end of the bore. In-water HDD may involve significant distance between the seabed and the drilling rig, and so a casing pipe may be required during the initial pilot hole drilling to provide some rigidity to the drill pipe as it is pushed ahead by the rig. Structures known as “goal posts” provide support for the casing pipe and are typically comprised of two driven piles with cross members set at predetermined elevations.
Port Dolphin has identified the need to install goal posts as part of the HDD drilling effort at the two water-to-water HDD locations. One potential option is that the goal posts are designed to self-install; however, another option is that drilling may be required. Further, at the shore-to-water transition HDD, Port Dolphin would need to install sheet piling to form a coffer dam, designed to contain the HDD exit pit so as to not impact nearby aquatic vegetation. Sheet pile segments would be installed by vibratory means.
Clam shell dredging would be required for passage under the Skyway Bridge and would be performed from a fixed working platform. Although dredging, followed by conventional lay and bury, is the most likely scenario, HDD remains a possibility for this segment. In the area near Manbirtee Key, a flotation ditch—dredging operations may require such a ditch when the minimum water depth necessary to safely float equipment is not present—would be dredged using conventional dredging equipment (i.e., the same barge that would be used to pull-in the shore approach HDD). The anticipated locations where the various methods of pipeline installation would be used are shown in Figure 1-3 of Port Dolphin's application.
There are eleven locations where tie-in operations would be required to piece the pipeline sections together. This mechanical operation is accomplished with specially designed connectors and a manned diving rig. This common operation does not require welding. Tie-ins would be required at each end of all HDD crossings, the Y-connection, and the PLEMs.
Construction Vessels—A shallow-water lay barge, spud barge and clamshell dredge, and a jack-up barge would be mobilized for offshore pipe-laying activities. Jack-up barges are mobile work platforms that are fitted with long support legs that can be raised or lowered; upon arrival at the work location the legs would be lowered and the barge itself raised above the water such that wave, tidal and current loading acts only on the relatively slender legs and not on the barge hull. A spud barge is a type of jack-up barge that typically offers increased stability but does not raise the hull above the water. This equipment would be used where conventional installation methods are anticipated. An HDD spread, including four jack-up barges, three hopper barges (designed to carry materials), and two tugs for barge towing, would be used for the three planned HDD segments. Four diving support vessels would also support tie-in and mattressing operations. Construction equipment would make one round-trip to the project location, staying on location for the duration of construction activity. Work crew vessels and supply vessels would make on average two trips a day for the duration of offshore construction. Work crew and supply vessels are expected to make between 420 and 450 round-trips to the offshore construction location from shore-based facilities for the duration of the project.
Table 1 details the vessels that would be used during the DWP and pipeline construction and installation activities. The projected duration and duty load of each vessel are also provided. Duty load is a primary consideration when characterizing project-related sound sources.
|Operation||Auxiliary equipment/notes||Engine specifications1||Operational usage2|
|DSV = Diving spread vessels|
|1All specifications are for diesel engines.|
|2All figures assume 24 hrs/day; percentages refer to percent maximum duty load.|
|Construction/Installation at DWP|
|Barge||N/A||3.5 months at 100%.|
|Anchor-handling support vessels||ROV winches, hydraulic pumps, thrusters, sonar, survey equipment||2 × 3,750-hp|
|Supply boat||Bow thruster||671-hp|
|Crew transfer boat||671-hp|
|Impact hammer||N/A||As required.|
|Jack-up: Port Manatee HDD||Jack-up||3,000-hp||27 days at 50%.|
|Spud lay barge: Shallow lay operation; no propulsion; uses two tugs||Tug||1,200-hp||59.4 days at 75%.|
|East jack-ups||Jack-up||3,000-hp||27 days at 75%.|
|West jack-ups||Jack-up||3,000-hp||27 days at 75%.|
|Pipelay barge: Large lay barge operation; no propulsion; uses two tugs||Tug||2,000-hp||37 days at 85%.|
|Dragline barge||600-hp||6 days at 100%.|
|Plow lay barge: Plow burial operation; no propulsion; uses two tugs||Tug||2,000-hp||113 days at 85%.|
|DSVs for mattress armoring||Vessel||1,000-hp||108 days at 100%.|
|DSVs for mattress armoring||Vessel||1,000-hp||12 days at 15%.|
|Pipeline gauge, fill, test, dewater, and drying||Vessel||300-hp||13 days at 35%.|
|Survey vessel||Vessel||1,000-hp||54 days at 50%.|
|Spud lay barge: Shallow lay barge operation; no propulsion; uses two tugs||Tug||1,200-hp||6.6 days at 15%.|
|East jack-ups||Jack-up||2,000-hp||3 days at 15%.|
|West jack-ups||Jack-up||2,000-hp||3 days at 15%.|
|Pipelay barge: Large lay barge operation; no propulsion; uses two tugs||Tug||2,000-hp||4 days at 15%.|
|Dragline barge||Barge||600-hp||1 day at 15%.|
|Plow lay barge: Plow burial operation; no propulsion; uses two tugs||Tug||2,000-hp||13 days at 15%.|
|DSVs for mattress armoring||Vessel||1,000-hp||12 days at 15%.|
|Pipeline gauge, fill, test, dewater, and drying||Vessel||300-hp||1 day at 15%.|
|Survey vessel||Vessel||1,000-hp||6 days at 15%.|
|Jack-up: Port Manatee HDD||Jack-up||3,000-hp||3 days at 15%.|
|Spud barge||Crane-mounted drill and vibratory drill; ancillary equipment includes welding equipment, air compressor, and generator||N/A||Maximum 4 days for vibratory drilling at each HDD location.|
|Tug||800-hp||Maximum 4 days for vibratory drilling at each HDD location.|
The proposed DWP operations would include SRV maneuvering/docking, regasification of LNG cargo, and debarkation. The SRVs are expected to approach the DWP from the south. In the open ocean, the SRVs typically travel at speeds of up to 19.5 kn (36.1 km/hr), reducing to less than 14 kn (25.9 km/hr) while maintaining full maneuvering speed. However, once approaching the vicinity of the DWP—within approximately 16 to 25 km (10-16 mi) of the DWP—the SRVs would begin approach by slowing to about half speed, and then to slow ahead. Inside of 5 km (3.1 km) from the DWP, the SRVs' main engines would be placed in dead slow ahead and decreased upon approach to dead slow, with final positioning and docking to occur using thrusters. Expected SRV transit, approach, and maneuvering/docking characteristics are outlined in Table 2. Only the maneuvering/docking activities and their associated sound sources (i.e., thrusters) are considered in this document; transit and approach maneuvers are considered part of routine vessel transit and are not considered further.
|Zone||Speed limit||Thrusters in use?|
|>33 km from DWP||Full service speed (19.5 kn)||No|
|25-33 km from DWP||Full maneuvering speed (<14 kn)||No|
|16-25 km from DWP||Half ahead (<10 kn)||No|
|5-16 km from DWP||Slow ahead (<6 kn)||No|
|Inside 5 km from DWP||Dead slow ahead (<4.5 kn, decreasing to <3 kn)||Bow and stern thrusters|
|Docking||Dead slow||Two bow thrusters; possibly one or two stern thrusters|
Based on a regasification cycle of approximately 8 days and projected DWP throughput during the first several years of 400 MMscfd, vessel traffic during operations is projected to consist of a maximum of 46 SRV trips per year. During DWP operations, sound would be generated by the maneuvering of SRVs upon approach to the Port, regasification of LNG aboard the SRVs, and subsequent debarkation from the Port.
Once an SRV is connected to a buoy, the vaporization of LNG and send-out of natural gas can begin. Each SRV would be equipped with up to five vaporization units, each with the capacity to vaporize 250 MMscfd. Under normal operation, two or more units would be in service simultaneously, with at least one unit on standby mode.
Method of Incidental Taking
Incidental take is anticipated to result from elevated levels of sound introduced into the marine environment by the construction and operation of the DWP, as described in preceding sections. Specifically, sound from pile driving, drilling, dredging, and vessel operations during the construction and installation phase, and sound from SRV maneuvering, docking, and regasification during operations would likely result in the behavioral harassment of marine mammals present in the vicinity. Table 3 shows these proposed activities by the time of year they are anticipated to occur.
|Construction and installation|
|Buoy installation||Summer 2013|
|Offshore impact hammering||Summer 2013|
|Pipelaying offshore||Late Summer 2013 through early Winter 2013-14|
|Pipelaying inshore||Late Summer 2013 through early Winter 2013-14|
|Offshore pipeline burial||Fall 2013 through Winter 2013-14|
|Inshore pipeline burial||Fall 2013 through Winter 2013-14|
|HDD vibratory driving||Summer 2013|
|SRV maneuvering/docking||Year-round; maximum 46 visits per year|
|Regasification||Year-round; 8 days estimated per visit|
During construction, underwater sound would be produced by construction vessels (e.g., barges, tugboats, and supply/service vessels) and machinery (e.g., pile driving and pipe laying equipment, trenching equipment, and goal post installation equipment at the HDD locations) operating either intermittently or continuously throughout the area during the construction period. Vessel traffic associated with construction would be a relatively continuous sound source during the construction phase. Vessel sound would be created by propulsion machinery, thrusters, generators, and hull vibrations and would vary with vessel and engine size. Machinery sound from underwater construction would be transmitted through water and would vary in duration and intensity. Port construction (i.e., field construction and installation operations) would require approximately 11 months.
While the main sound source during SRV transit and approach to the DWP would originate from the SRV main engines (i.e., predominantly in low frequencies), the primary sound source during maneuvering and docking would be the SRV thrusters. An additional underwater sound source would be the sound produced by the flow of gas through the proposed pipeline, although very little sound would be expected to result (JASCO, 2008); therefore, this source is not considered further.
Description of Sound Sources Back to Top
Sound travels in waves, the basic components of which are frequency, wavelength, velocity, and amplitude. Frequency is the number of pressure waves that pass by a reference point per unit of time and is measured in hertz (Hz) or cycles per second. Wavelength is the distance between two peaks of a sound wave; lower frequency sounds have longer wavelengths than higher frequency sounds, which is why the lower frequency sound associated with the proposed activities would attenuate more rapidly in shallower water. Amplitude is the height of the sound pressure wave or the “loudness” of a sound and is typically measured using the decibel (dB) scale. A dB is the ratio between a measured pressure (with sound) and a reference pressure (sound at a constant pressure, established by scientific standards), and is a logarithmic unit that accounts for large variations in amplitude; therefore, relatively small changes in dB ratings correspond to large changes in sound pressure. When referring to sound pressure levels (SPLs; the sound force per unit area), sound is referenced in the context of underwater sound pressure to 1 microPascal (μPa). One pascal is the pressure resulting from a force of one newton exerted over an area of one square meter. The source level (SL) represents the sound level at a distance of 1 m from the source (referenced to 1 μPa). The received level is the sound level at the listener's position.
Root mean square (rms) is the quadratic mean sound pressure over the duration of an impulse. Rms is calculated by squaring all of the sound amplitudes, averaging the squares, and then taking the square root of the average (Urick, 1975). Rms accounts for both positive and negative values; squaring the pressures makes all values positive so that they may be accounted for in the summation of pressure levels (Hastings and Popper, 2005). This measurement is often used in the context of discussing behavioral effects, in part because behavioral effects, which often result from auditory cues, may be better expressed through averaged units than by peak pressures.
When underwater objects vibrate or activity occurs, sound-pressure waves are created. These waves alternately compress and decompress the water as the sound wave travels. Underwater sound waves radiate in all directions away from the source (similar to ripples on the surface of a pond), except in cases where the source is directional. The compressions and decompressions associated with sound waves are detected as changes in pressure by aquatic life and man-made sound receptors such as hydrophones.
The underwater acoustic environment consists of ambient sound, defined as environmental background sound levels lacking a single source or point (Richardson et al., 1995). The ambient underwater sound level of a region is defined by the total acoustical energy being generated by known and unknown sources, including sounds from both natural and anthropogenic sources. These sources may include physical (e.g., waves, earthquakes, ice, atmospheric sound), biological (e.g., sounds produced by marine mammals, fish, and invertebrates), and anthropogenic sound (e.g., vessels, dredging, aircraft, construction). Even in the absence of anthropogenic sound, the sea is typically a loud environment. A number of sources of sound are likely to occur within Tampa Bay and the adjoining shelf, including the following (Richardson et al., 1995):
- Wind and waves: The complex interactions between wind and water surface, including processes such as breaking waves and wave-induced bubble oscillations and cavitation, are a main source of naturally occurring ambient sound for frequencies between 200 Hz and 50 kHz (Mitson, 1995). In general, ambient sound levels tend to increase with increasing wind speed and wave height. Surf sound becomes important near shore, with measurements collected at a distance of 8.5 km (5.3 mi) from shore showing an increase of 10 dB in the 100 to 700 Hz band during heavy surf conditions.
- Precipitation sound: Sound from rain and hail impacting the water surface can become an important component of total sound at frequencies above 500 Hz, and possibly down to 100 Hz during quiet times.
- Biological sound: Marine mammals can contribute significantly to ambient sound levels, as can some fish and shrimp. The frequency band for biological contributions is from approximately 12 Hz to over 100 kHz.
- Anthropogenic sound: Sources of ambient sound related to human activity include transportation (surface vessels and aircraft), dredging and construction, oil and gas drilling and production, seismic surveys, sonar, explosions, and ocean acoustic studies (Richardson et al., 1995). Shipping sound typically dominates the total ambient sound for frequencies between 20 and 300 Hz. In general, the frequencies of anthropogenic sounds are below 1 kHz and, if higher frequency sound levels are created, they would attenuate (decrease) rapidly (Richardson et al., 1995). Typical SPLs for various types of ships are presented in Table 4.
|Vessel description||Frequency (Hz)||Source level (dB)|
|Source: Richardson et al., 1995.|
|Outboard drive; 23 ft; 2 engines @ 80 hp||630||156|
|Twin diesel; 112 ft||630||159|
|Small supply ships; 180-279 ft||1,000||125-135 (at 50 m)|
|Freighter; 443 ft||41||172|
The sum of the various natural and anthropogenic sound sources at any given location and time—which comprise “ambient” or “background” sound—depends not only on the source levels (as determined by current weather conditions and levels of biological and shipping activity) but also on the ability of sound to propagate through the environment. In turn, sound propagation is dependent on the spatially and temporally varying properties of the water column and sea floor, and is frequency-dependent. As a result of the dependence on a large number of varying factors, the ambient sound levels at a given frequency and location can vary by 10-20 dB from day to day (Richardson et al., 1995).
Very few measurements of ambient sound from Tampa Bay and the adjoining shelf are available. There are no specific data on ambient underwater sound levels for the area of the proposed Port and pipeline route. Shooter et al. (1982) analyzed approximately 12 hours of data collected in deep (3,280 m) waters in the western GOM and reported median ambient sound levels of 77-80 dB re: 1 μPa  /Hz. These levels are likely to be somewhat lower than those occurring in the vicinity of Tampa Bay, due in large part to the reduced contribution from surf in deep water.
Known sound levels and frequency ranges associated with anthropogenic sources similar to those that would be used for this project are summarized in Table 5. Details of each of the sources are described in the following text.
|Source||Activity||Location||Maximum broadband source level (re: 1 µPa)|
|Source: JASCO, 2008, 2010.|
|1Source level for impact hammer estimated assuming pulse length of 100 ms.|
|Barge||Anchor installation operations||STL buoys (DWP)||177 dB|
|Tug||Anchor installation operations||STL buoys (DWP)||205 dB|
|Impact hammer1||Pile driving||STL buoys (DWP)||217 dB|
|Barge||Pipe laying||Pipeline corridor, DWP to shore||174 dB|
|Dredge||Dredging||Likely inshore, offshore if necessary||188 dB|
|HDD||Drilling||Two locations in Tampa Bay||157 dB|
|Vibratory driving||Sheet pile installation||Two locations in Tampa Bay||186 dB|
|SRV||Maneuvering/docking, with thrusters||DWP||183 dB|
The sounds produced by these activities fall into one of two sound types: Pulsed and non-pulsed (defined in next paragraph). The distinction between these two general sound types is important because they have differing potential to cause physical effects, particularly with regard to hearing (e.g., Ward, 1997 in Southall et al., 2007). Please see Southall et al. (2007) for an in-depth discussion of these concepts.
Pulsed sounds (e.g., explosions, gunshots, sonic booms, impact pile driving) are brief, broadband, atonal transients (ANSI, 1986; Harris, 1998) and occur either as isolated events or repeated in some succession. Pulsed sounds are all characterized by a relatively rapid rise from ambient pressure to a maximal pressure value followed by a decay period that may include a period of diminishing, oscillating maximal and minimal pressures. Pulsed sounds generally have an increased capacity to induce physical injury as compared with sounds that lack these features.
Non-pulse (intermittent or continuous) sounds can be tonal, broadband, or both. Some of these non-pulse sounds can be transient signals of short duration but without the essential properties of pulses (e.g., rapid rise time). Examples of non-pulse sounds include those produced by vessels, aircraft, machinery operations such as drilling or dredging, vibratory pile driving, and active sonar systems. The duration of such sounds, as received at a distance, can be greatly extended in a highly reverberant environment. Many of the sounds produced by the project would be transient in nature (i.e., the source moves), such as during vessel docking. Regasification sounds are continuous (while the SRV is docked) and stationary. The positioning (maneuvering and docking) of SRVs using thrusters is intermittent (i.e., every 8 days) and of short duration (i.e., 10 to 30 minutes).
For this project, the only pulsive sounds are associated with pile driving activities at the offshore Port location (i.e., associated with anchor installation activities). Impact hammers (proposed for use in driving buoy anchors) operate by repeatedly dropping a heavy piston onto a pile to drive the pile into the substrate. Sound generated by impact hammers is characterized by rapid rise times and high peak levels, a potentially injurious combination (Hastings and Popper, 2005). Vibratory hammers, which would be used to install sheet pile and possibly pilings for goal posts inshore, install piles by vibrating them and allowing the weight of the hammer to push them into the sediment. Vibratory hammers produce significantly less sound than impact hammers. Peak SPLs may be 180 dB or greater but are generally 10 to 20 dB lower than SPLs generated during impact pile driving of the same-sized pile (Caltrans, 2009). Rise time is slower, reducing the probability and severity of injury (USFWS, 2009), and sound energy is distributed over a greater amount of time (Nedwell and Edwards, 2002; Carlson et al., 2001).
Sound Attenuation Devices
Sound levels can be greatly reduced during impact pile driving using sound attenuation devices. There are several types of sound attenuation devices including bubble curtains, cofferdams, and isolation casings (also called temporary sound attenuation piles [TNAP]), and cushion blocks. Port Dolphin considers the installation of cofferdams to be infeasible for this project. The information available suggests that bubble curtains, cushion blocks and caps, and TNAP design offer comparable levels of sound attenuation for pile driving. Port Dolphin proposes to implement one or more of these techniques during the pile driving activities needed to install components of the STL buoys and will make a final decision with regard to the technology to be used prior to beginning work.
Bubble curtains create a column of air bubbles rising around a pile from the substrate to the water surface. The air bubbles absorb and scatter sound waves emanating from the pile, thereby reducing the sound energy. Bubble curtains may be confined or unconfined. An unconfined bubble curtain may consist of a ring seated on the substrate and emitting air bubbles from the bottom. A confined bubble curtain contains the air bubbles within a flexible or rigid sleeve made from plastic, cloth, or pipe. Confined bubble curtains generally offer higher attenuation levels than unconfined curtains because they may physically block sound waves and they prevent air bubbles from migrating away from the pile. For this reason, the confined bubble curtain is commonly used in areas with high current velocity (Caltrans, 2009).
An isolation casing is a hollow pipe that surrounds the pile, isolating it from the in-water work area. The casing is dewatered before pile driving. This device provides levels of sound attenuation similar to that of bubble curtains (Caltrans, 2009). Sound levels can be reduced by 8 to 14 dB. Cushion blocks consist of materials (e.g., wood, nylon) placed atop piles during impact pile driving activities to reduce source levels. Typically sound reduction can range from 4 to a maximum of 26 dB.
Both environmental conditions and the characteristics of the sound attenuation device may influence the effectiveness of the device. According to Caltrans (2009):
- In general, confined bubble curtains attain better sound attenuation levels in areas of high current than unconfined bubble curtains. If an unconfined device is used, high current velocity may sweep bubbles away from the pile, resulting in reduced levels of sound attenuation.
- Softer substrates may allow for a better seal for the device, preventing leakage of air bubbles and escape of sound waves. This increases the effectiveness of the device. Softer substrates also provide additional attenuation of sound traveling through the substrate.
- Flat bottom topography provides a better seal, enhancing effectiveness of the sound attenuation device, whereas sloped or undulating terrain reduces or eliminates its effectiveness.
- Air bubbles must be close to the pile; otherwise, sound may propagate into the water, reducing the effectiveness of the device.
- Harder substrates may transmit ground-borne sound and propagate it into the water column.
The literature presents a wide array of observed attenuation results for bubble curtains (see, e.g., WSF, 2009; WSDOT, 2008; USFWS, 2009; Caltrans, 2009). The variability in attenuation levels is due to variation in design, as well as differences in site conditions and difficulty in properly installing and operating in-water attenuation devices. As a general rule, reductions of greater than 10 dB cannot be reliably predicted (Caltrans, 2009).
Sound Thresholds Back to Top
Since 1997, NMFS has used generic sound exposure thresholds to determine when an activity in the ocean that produces sound might result in impacts to a marine mammal such that a take by harassment or injury might occur (NMFS, 2005b). To date, no studies have been conducted that examine impacts to marine mammals from which empirical sound thresholds have been established. Current NMFS practice regarding exposure of marine mammals to high level sounds is that cetaceans exposed to impulsive sounds of 180 dB rms or above are considered to have been taken by Level A (i.e., injurious) harassment. Behavioral harassment (Level B) is considered to have occurred when marine mammals are exposed to sounds at or above 160 dB rms for impulse sounds (e.g., impact pile driving) and 120 dB rms for continuous sound (e.g., vessel sound, vibratory pile driving) but below injurious thresholds.
Distance to Sound Thresholds
This section details sound source modeling produced under contract by the applicant (JASCO, 2008, 2010) and describes the predicted distances to relevant regulatory sound thresholds for the specified activities. NMFS has determined that this information represents the best information available for project sound sources and has used the information to develop mitigation measures and to estimate potential incidental take in this document. The modeling scenarios considered all sound sources associated with the project and were developed to thoroughly characterize the various construction/installation and operation activities expected. The relevant information is summarized in Table 6. The equipment list associated with each activity is based on current construction plans for the Port (Ocean Specialists, 2007). For each piece of equipment specified, proxy vessels were selected from JASCO Research's database of underwater sound measurements. The sound propagation model used several parameters, including expected water column sound speeds, bathymetry (water depth and shape of the ocean bottom), and bottom geoacoustic properties (which indicate how much sound is reflected off of the ocean bottom), to estimate the radii of sound impacts (JASCO, 2008). Modeling scenario locations are depicted in Figure 1-4 of Port Dolphin's application. Please see Appendices C and D in Port Dolphin's application for a detailed description of this sound source modeling.
|Activity||Source||Modeled location||Distance to threshold 1,2||Approximate area encompassed by threshold2|
|Source: JASCO, 2008, 2010.|
|1All distances are unweighted, 95th percentile radial distances.|
|2For distances not given precisely (e.g., <0.2 km) area of ensonification was modeled using a radial distance of 200 m. Although the distance to threshold would be less than 200 m, it is not possible to specifically calculate the distance because the scenarios involve multiple vessel components.|
|Buoy installation||Crane vessel, cargo barge, support vessel||North STL buoy; offshore DWP site||180 dB: <0.2 km 120 dB: 3.9 km||180 dB: <0.13 km2 120 dB: 48 km2|
|Impact hammering||Impact hammer||Y-connector; offshore DWP site||180 dB: 0.18 km 160 dB: 4.5 km||180 dB: 0.10 km2 160 dB: 64 km2|
|Pipelaying, offshore||Barge, two anchor handling tugs, support tug||15-m isobath||180 dB: <0.2 km 120 dB: 7.5 km||180 dB: <0.13 km2 120 dB: 177 km2|
|Pipelaying, inshore||Barge, two anchor handling tugs, support tug||Tampa Bay||180 dB: <0.2 km 120 dB: 6.0 km||180 dB: <0.13 km2 120 dB: 113 km2|
|Pipeline burial, offshore||Plow system, two anchor handling tugs||15-m isobath||180 dB: <0.2 km 120 dB: 8.4 km||180 dB: <0.13 km2 120 dB: 222 km2|
|Pipeline burial, inshore||Plow system, two anchor handling tugs||Tampa Bay||180 dB: <0.2 km 120 dB: 6.7 km||180 dB: <0.13 km2 120 dB: 141 km2|
|HDD||Floating spud barge, crane mounted drill, welding equipment, air compressor, generator||Tampa Bay||180 dB: <0.01 km 120 dB: 0.24 km||180 dB: <0.00 km2 120 dB: 0.2 km2|
|HDD vibratory driving||Floating spud barge, vibrator, welding equipment, air compressor, generator||Tampa Bay||180 dB: <0.01 km 120 dB: 12.6 km||180 dB: <0.00 km2 120 dB: 499 km2|
|Docking at buoy, dead slow, two bow thrusters and one stern thruster||SRV||STL buoy; offshore DWP site||180 dB: <0.01 km 120 dB: 3.6 km||180 dB: <0.00 km2 120 dB: 41 km2|
|Regasification||SRV||STL buoy; offshore DWP site||180 dB: 0.00 km 120 dB: 0.17 km||180 dB: <0.00 km2 120 dB: 0.09 km2|
Note that in many cases the scenarios involve multiple pieces of equipment. Although equipment spacing would vary during the course of operations, a single layout must be assumed for modeling purposes. As such, where multiple vessels were involved in the scenarios listed in Table 6 the following layout was assumed:
- The barge used for the main operation in each scenario (e.g., crane vessel, pipe laying barge, pipe burial barge) was set in the middle of the group of vessels.
- For four or fewer tugs (anchor handling and/or support), tugs were spaced at a range of 100 m (328 ft) from the center of the barge. Note that the pipe laying/burial barge itself is 122 m long x 30 m wide (400 x 100 ft).
The radii to sound thresholds vary for the same activity depending on water depth, because the transmission of lower-frequency sound waves can be significantly reduced in shallower water. As a result, the radii to the Level A and Level B harassment isopleths in Tampa Bay (i.e., shallower water) are shorter than those that would occur offshore. In addition, much of the energy from the vessels associated with pipelaying occurs at low frequencies and would propagate poorly in shallower water.
Although sounds created by construction equipment and vessels would be continuous during pipeline installation, activities would progress slowly along the pipeline route as the pipeline is laid and buried and the trench backfilled. Any one area would be subject to the maximum sound levels for only 1 to 2 days at a time as the construction activities pass that area. Sound modeling indicates that, overall, operational sound associated with the proposed project is consistent with other man-made underwater sound sources in the area (e.g., commercial shipping and dredging). Appendix E of Port Dolphin's application presents Level B harassment sound field graphics for construction activities.
Specific Activity Descriptions—As described previously, the applicant provided detailed sound source modeling for all sound-producing activities associated with the project. In the following sections, each specific type of activity is described in terms of the modeling scenario; the type, duration, and timing of sound produced by the activity; and the radial distances to relevant sound thresholds. All radial distances to thresholds presented in the following sections are modeled, and may be different from the actual distances as determined through site-specific acoustic monitoring conducted during the specified activities.
Buoy Installation—Proxies were selected for the crane and support vessels based on vessel specifications. While a cargo barge may be present on-site for a portion of the operations, Port Dolphin assumed that this barge would typically not be under power. Installation of the buoys at the Port would produce continuous sound for a relatively short period of time during summer, with the 120-dB isopleth located 3.9 km (2.4 mi) from each STL buoy location.
Impact Pile Driving—During the construction period, impact hammering would produce the loudest sound levels but would likely occur only for short periods of time. The source depth for pile driving was set to approximately half the local water depth. In actuality, sound would radiate from all portions of the pilings; this midwater column value is a precautionary estimate of the depth for an equivalent point source, as losses due to bottom and surface interactions would be less for a source at mid-depth than for one near the sea floor or surface. Impact hammering operations would involve a pipe lay barge and tugs, similar to pipe laying operations. However, because the potential impact to marine mammals is different for impulsive and continuous sources, impact hammering sound (an impulsive source) is considered separately from vessel sound (non-pulsed sources). Note that the source levels from impact hammering are much higher than those from the vessels that are likely to be on-site. Impact hammering offshore would encompass an area with a radius of approximately 180 m (591 ft) to the Level A threshold; radii to the 160-dB isopleths for this impulsive source would be at 4.5 km (2.8 mi).
Pipe Laying—Pipe laying activities would generate continuous, transient, and variable sound levels during construction predominantly during fall, with some activity during late summer and early winter. Two sites were selected for pipe laying: one approximately midway along the offshore portion of the pipeline and another along the inshore portion. Equipment lists for the offshore and inshore sites are identical: a pipe laying barge, two tugs involved in re-setting of anchors, and a third tug in transit. Sound impacts from pipelaying would produce a 6.0 or 7.5 km (3.7-4.7 mi) radius to the 120-dB isopleth inshore and offshore, respectively.
Pipe Burial—Pipeline burial using the plow system would generate continuous, transient, and variable sound levels during construction, primarily during fall and winter. Pipeline burial would be used infrequently during the construction period. Similarly to pipe laying, pipe burial using a trenching plow system would consist of an anchored barge accompanied by two anchor handling tugs. In addition, sound would be generated by the plow used to bury the pipeline. Detailed source level data were not available for plow operations. However, Aspen Environmental Group (2005) reported a broadband source level of 185 dB. Based on this information, similar source levels from dredge operations (Greene, 1987) were used for the applicant's modeling purposes. Note that the dredge source levels include the sound from the barge upon which the dredge is operated; consequently, a separate barge is not specified for plowing operations in Table 6. The modeling scenario used the depth of the barge hull under the water as the sound source depth, rather than the depth of the actual dredge work. This is because observations from clamshell dredging show that the highest levels of underwater sound are emitted from equipment on the barge (propagating through the hull) rather than from the scraping sounds of the dredge itself (Richardson et al., 1995). Pipeline burial using the plow system produces sound attenuating to the 120-dB isopleth at 6.7 km (4.2 mi) inshore and 8.4 km (5.2 mi) offshore.
HDD—HDD within Tampa Bay would produce continuous sound levels and is expected to occur during summer. Installation of the goal posts (described previously under “Pipeline Installation”) at each HDD location would produce a continuous sound for a relatively short period of time and would only occur during summer. HDD would be employed for installation of the pipeline at a number of locations along the inshore portion of the route, including the Port Manatee shore approach and two crossings of the existing Gulfstream pipeline. Drilling and vibratory driving (for goal posts/sheet pile) would be conducted from a floating spud barge approximately 41 m in length. Drilling would involve a crane-mounted drill, suspended from a crawler crane on the barge. The barge would also be equipped with welding equipment, an air compressor, and a generator.
Source levels for drilling of the pilot holes are based on measurements made by Greene (1987) during drilling operations in the Beaufort Sea. As with drilling from a barge, these measurements include contributions from both the drill assembly itself and from equipment on the drill platform (e.g., generators). Because the dominant sound source is equipment located on the drilling vessel (Richardson et al., 1995) rather than the drilling or scraping itself, a source level height of 2.2 m was used, as it was for other barge-mounted activities modeled by JASCO.
Source levels for the vibratory driver were derived from measurements made by JASCO. The vibratory driver was mounted on a moored barge during the measurements, and so sound contributions from equipment on the barge are included in the source level estimates. The measured driver is larger than the vibratory driver planned for use at Port Dolphin. However, very few measurements of underwater sound exist for pile drivers of this size, and in most cases the available reports do not describe the vibratory driver used. Additionally, scaling by vibratory driver specifications (e.g., the eccentric moment) is made difficult by the fact that pile driving source levels depend not only on the equipment but also on the piling, substrate and environment. As such, JASCO's un-scaled measurements of underwater sound are used here as a conservative estimate of the sound likely to be generated during installation of the goal posts/sheet pile. As for the impact pile driving described previously, the source depth for pile driving was conservatively set to half the local water depth, i.e., 3.5 m.
Modeling results (JASCO, 2010) indicate that the 120-dB isopleth would extend 240 m (787 ft) from the drilling operation, while the 120-dB isopleth for HDD vibratory driving would extend 12.6 km (7.8 mi) from the source.
SRV Docking—Once the SRV completes its approach to Port Dolphin and is within approximately 5.6 km (3.5 mi) of the Port, bow and stern thrusters would be utilized. Thruster use would vary, operating for 10 to 30 minutes to allow for the proper positioning of the vessel and for connection to the STL buoy. Docking or berthing would occur at alternate STL buoys approximately every 8 days. Sound modeling, assessing the periodic use of the thrusters (i.e., every 8 days) producing an intermittent and moving sound, indicated that the 120-dB isopleth would occur at 3.6 km (2.2 mi) from the SRV.
Operational procedures for the SRVs specify probable use of thrusters during approach and docking. Speed is gradually reduced as the SRV approaches the unloading buoys, until main propulsion is at dead slow. Bow and stern thrusters are used during docking. Once moored, ship's propulsion is not required for positioning. Based on these operational procedures, the sample situation described in Table 6 was selected for modeling; i.e., docking at the northern buoy, using both bow thrusters and one stern thruster.
Very little information is available on the underwater sound levels produced by LNG carriers. However, some data and empirical formulas have been developed for large tankers in general. At typical cruising speeds, source levels from such vessels are dominated by propeller cavitation (Sponagle, 1988; Seol et al., 2002). As described by LGL and JASCO (2005), an empirical expression for the source spectrum level (1 Hz bandwidth) in the frequency range between 100 Hz and 10 kHz is
where B is the number of blades, D is the propeller diameter in meters, N is the number of propeller revolutions per second, and f is the frequency in Hz. For frequencies less than 100 Hz, the source level is assumed to be constant at the 100 Hz level. In the case of ducted propellers (e.g., bow and stern thrusters), the constant is approximately 7 dB larger. Specifications for the main propulsion system are based on a typical carrier, and are similar to those described by LGL and JASCO (2005). Bow and stern thrusters are expected to be single-speed, controllable-pitch devices, with power ratings of 2,000 kW each for the bow thrusters and 1,200 kW each for the stern thrusters. Based on these values, diameters and rates of revolution for the thrusters were based on specifications for the most common models currently available. The above model is not able to take into account the reduction in source levels that would result from a change in pitch at lower power outputs; hence, the modeled source levels are conservative (i.e., represent maximum expected levels of underwater sound).
Regasification—The SRV would regasify its LNG cargo while moored at the STL buoy. Sound levels for regasification are low, and the modeling predicts that the 120-dB isopleths would be only 170 m (558 ft) from the source.
The following additional sources of underwater sound are expected to be present during construction of the DWP, but were not modeled:
- Dredging: Dredging would be involved in a few stages of construction, including HDD (discussed later) and pipelaying at the Sunshine Bridge crossing (Ocean Specialists, 2007). This would involve a clamshell or bucket-style dredge, operated from a barge while one or more additional barges carry out other tasks nearby. Measurements taken by JASCO during operation of a clamshell dredge indicated source levels of approximately 150-155 dB, i.e., roughly 20 dB lower than the source levels associated with the barge used during pipe laying operations. As such, dredging may be considered an insignificant source of sound compared with operation of the barges that would also be present.
- Transponders: Once the port is operational, an additional source of underwater sound in the vicinity of the unloading buoys would be the acoustic transponders installed on the buoys. Information was not available on the specific transponders intended for use at the DWP; however, specifications from commercially available buoy positioning transponders indicate operating frequencies of a few tens of kHz, and source levels of approximately 190 dB. Given this estimated broadband source level, we may estimate ranges to various threshold values assuming simple spherical spreading, i.e., RL = SL − 20log 10 (r). Solving for r shows that received levels would drop to 180 dB at a range of approximately 3 m, and to 160 dB at a range of approximately 32 m; further, this sound source would be highly intermittent, as the transponders would only transmit, briefly, when interrogated by the SRV-based command unit. As such, only marine mammals passing very near the unloading buoys during the brief period of transmittance would potentially be affected, and effects from these sources may be considered discountable.
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On March 1, 2011, NMFS published a notice of receipt of an application for a Letter of Authorization (LOA) in the Federal Register (76 FR 11205) and requested comments and information from the public for 30 days. NMFS did not receive any substantive comments. Description of Marine Mammals in the Area of the Specified Activity
Twenty-nine marine mammals (28 cetaceans and the Florida manatee [Trichechus manatus]) have documented occurrences in the GOM (Wursig et al., 2000). The manatee is under the jurisdiction of the U.S. Fish and Wildlife Service, and will not be discussed further in this document. Of the cetaceans, seven are mysticetes (baleen whales) and 21 are odontocetes (toothed whales, including dolphins). Table 7 contains a summary of relevant information for each of these 28 species.
|Source: Würsig et al., 2000|
|aStatus: E = Listed as endangered under the Endangered Species Act.|
|bOccurrence: 1 = extralimital; 2 = rare; 3 = uncommon; 4 = common.|
|cBeaked whales in the GOM may be somewhat more common than survey data indicate, as beaked whales are difficult to sight and identify to species. Most surveys have been conducted in sea states that are not optimal for sighting beaked whales.|
|North Atlantic right whale (Eubalaena glacialis)||E||1||X||X|
|Blue whale (Balaenoptera musculus)||E||1||X||X|
|Bryde's whale (Balaenoptera edeni)||3||X||X|
|Fin whale (Balaenoptera physalus)||E||2||X||X|
|Humpback whale (Megaptera novaeangliae)||E||2||X||X|
|Minke whale (Balaenoptera acutorostrata)||2||X||X|
|Sei whale (Balaenoptera borealis)||E||2||X||X|
|Family Physeteridae:||Dwarf sperm whale (Kogia sima)||3||X||X|
|Pygmy sperm whale (Kogia breviceps)||3||X||X|
|Sperm whale (Physeter macrocephalus)||E||4||X||X|
|Blainville's beaked whale (Mesoplodon densirostris)||2c||X||X|
|Cuvier's beaked whale (Ziphius cavirostris)||2c||X||X|
|Gervais' beaked whale (Mesoplodon europaeus)||3c||X||X|
|Sowerby's beaked whale (Mesoplodon bidens)||1c||X||X|
|Atlantic spotted dolphin (Stenella frontalis)||4||X||X||X|
|Bottlenose dolphin (Tursiops truncatus)||4||X||X||X|
|Clymene dolphin (Stenella clymene)||4||X||X|
|False killer whale (Pseudorca crassidens)||3||X||X|
|Fraser's dolphin (Lagenodelphis hosei)||4||X||X|
|Killer whale (Orcinus orca)||3||X|
|Melon-headed whale (Peponocephala electra)||4||X|
|Pantropical spotted dolphin (Stenella attenuata)||4||X||X|
|Pygmy killer whale (Feresa attenuata)||3||X||X|
|Short-finned pilot whale (Globicephala macrorhynchus)||4||X||X|
|Risso's dolphin (Grampus griseus)||4||X||X|
|Rough-toothed dolphin (Steno bredanensis)||4||X||X|
|Spinner dolphin (Stenella longirostris)||4||X||X|
|Striped dolphin (Stenella coeruleoalba)||4||X||X|
Of these 28 cetacean species, based on available survey data, only the bottlenose dolphin and Atlantic spotted dolphin are likely to occur regularly in the vicinity of the project area (i.e., coastal and shelf waters of the eastern GOM) (Fulling et al., 2003). Because a small portion of the sound produced by the activity is predicted to extend into the mid-shelf depth stratum, three other species of cetacean—pygmy and dwarf sperm whales and the rough-toothed dolphin—could be affected. Other species of dolphins and an occasional whale are sometimes observed in nearshore GOM waters and might infrequently strand, but these are not considered normal occurrences for those deepwater species that occur more regularly in waters around and seaward of the continental shelf break (Mullin and Fulling, 2003a; Mullin et al., 2004). As a result, the potential effects of the specified activity are analyzed only for these five species. As the species to be most affected by the specified activity, bottlenose and spotted dolphin occurrences relative to the project area are discussed in more detail in the following paragraphs.
The cetacean fauna of the northern and eastern GOM continental shelf, including the project area, typically consists of the bottlenose dolphin and the Atlantic spotted dolphin (Davis and Fargion, 1996; Jefferson and Schiro, 1997; Davis et al., 1998; Davis et al., 2000; Würsig et al., 2000). At the shelf edge and within the deeper waters of the continental slope, the cetacean community typically includes nineteen species, including the Bryde's whale, sperm whale, pygmy and dwarf sperm whales, three species of beaked whales, and twelve species of oceanic dolphins. Oceanographic and bathymetric features (e.g., eddies, water temperature, salinity) are important factors in determining the distribution of marine mammals, in large part because the presence of prey is frequently influenced by such features (Katona and Whitehead, 1988; Biggs et al., 2000; Wormuth et al., 2000; Davis et al., 2002). The presence of specific hydrographic and/or bathymetric features and discontinuities (e.g., abrupt temperature differentials, current edges, upwelling areas, sea mounts, banks, shoals, the continental shelf edge) may also affect marine mammal distribution (USDON, 2003).
The following discussions of the population status of GOM marine mammals use categories adapted from Würsig et al. (2000):
- Common: A species that is abundant and widespread throughout the region in which it occurs;
- Uncommon: A species that does not occur in large numbers and may or may not be widely distributed throughout the region in which it occurs;
- Rare: A species present in such small numbers throughout the region that it is seldom seen; and
- Extralimital: A species known on the basis of few records that are probably the result of unusual movements of few individuals into the region.
Data historically acquired during aerial and shipboard surveys conducted within the eastern GOM were analyzed by marine mammal researchers and summarized in USDON (2003). To increase the utility of the species sightings data, marine mammal occurrence and distribution data were partitioned into both seasonal and water depth categories. This partitioning is supported by distribution patterns (e.g., sightings over the continental shelf, sightings beyond the continental shelf) observed during large‐scale surveys (e.g., Cetacean and Turtle Assessment Program [CETAP] surveys; CETAP, 1982; Hain et al., 1985; Winn et al., 1987). Seasonal categories included in USDON (2003) and employed in this analysis were:
- Winter: December 21 through March 20;
- Spring: March 21 through June 20;
- Summer: June 21 through September 20; and
- Fall: September 21 through December 20.
Water depth categories, or depth strata, included in USDON (2003) and employed in this analysis were as follows:
- Nearshore: 0 to 120 ft (0 to 36.6 m);
- Mid‐shelf: 120 to 300 ft (36.6 to 91.4 m);
- Shelf‐edge: 300 to 6,600 ft (91.4 to 2,000 m); and
- Slope:> 6,600 ft (> 2,000 m).
The U.S. Department of the Navy (USDON, 2003) reviewed available marine mammal survey data for the eastern GOM and summarized species presence and distribution on a seasonal basis. Relevant findings pertinent to marine mammals include the following:
- Spring is the season with the highest number of cetacean occurrence records, although high numbers of cetacean occurrence records were also noted for summer;
- Fall and winter are the two seasons with the lowest number of occurrence records and total number of cetaceans;
- Higher numbers in spring and summer are possibly due to the higher survey effort usually expended during those months (when sighting conditions are optimal); and
- There are fewer sighting records in fall than in the other seasons, likely attributable to suboptimal survey conditions (i.e., reduction in sightability).
The Bryde's whale is the most frequently sighted mysticete in the Gulf, though considered uncommon. Strandings and sightings data suggest that this species may be present throughout the year, generally in the northeastern Gulf near the 100-m (328-ft) isobath between the Mississippi River delta and southern Florida (Davis et al., 2000; Würsig et al., 2000). The remaining six mysticete whales (blue, fin, humpback, minke, sei, and North Atlantic right whales) are considered rare or extralimital in the GOM (Jefferson, 1996; Jefferson and Schiro, 1997). Mysticete whales, including the Bryde's whale, could occur within the project area although such occurrence would be extremely unlikely.
Bottlenose dolphins and spotted dolphins are known to occur regularly in the project area and are the species to be most affected by the project. In addition, there is some possibility that pygmy and dwarf sperm whales and rough-toothed dolphins could occur in deeper waters ensonified by some offshore project activities. Most of the odontocetes known to occur within the Gulf (Table 7) are considered common. Exceptions include the beaked whales, with most being rare or extralimital, and the dwarf and pygmy sperm whales, which are considered uncommon. The frequency of occurrence of beaked whales and dwarf and pygmy sperm whales are most likely underestimated because these cryptic species are submerged much of the time and avoid aircraft and ships (Würsig et al., 1998). Consequently, these species may be somewhat more common than is indicated by survey data but are still likely to be relatively uncommon. The sperm whale is considered common in the Gulf (Jefferson, 1996; Jefferson and Schiro, 1997; Davis et al., 2000; Waring et al., 2006). Sightings data suggest a Gulf‐wide distribution on the continental slope. Congregations of sperm whales are common along the continental shelf edge in the vicinity of the Mississippi River delta in water depths of 500 to 2,000 m (1,640-6,562 ft). As a result of these consistent sightings, it is believed that there is a resident population of sperm whales in the Gulf consisting of adult females, calves, and immature individuals (Brandon and Fargion, 1993; Mullin et al., 1994; Sparks et al., 1993; Jefferson and Schiro, 1997). Though most odontocetes (including delphinids) are considered common in the GOM, they prefer waters of the continental shelf edge (approximately 200 m [656 ft]) or deeper waters of the continental slope. Therefore, it is unlikely that these species would occur within the project area (i.e., Tampa Bay and nearshore waters). Due to the rarity of the majority of odontocete species, as well as the mysticetes discussed previously, in the proposed project area and the remote chance they would be affected by Port Dolphin's proposed port operations, these species are not considered further in this analysis.
The most commonly sighted cetaceans on the GOM continental shelf (in terms of numbers of individual sightings) during systematic surveys conducted in the mid to late 1990s (i.e., GulfCet II) were bottlenose dolphins and Atlantic spotted dolphins. Brief discussions of these commonly sighted marine mammal species are provided in the following subsections.
Bottlenose dolphins—The bottlenose dolphin is a common inhabitant of both the continental shelf and slope in the GOM, generally in waters less than 20 m (66 ft) (Griffin and Griffin, 2003). The species is also distributed throughout the bays, sounds, and estuaries of the GOM (Mullin et al., 1990). Bottlenose dolphins are opportunistic feeders, taking a wide variety of fish, cephalopods, and shrimp (Wells and Scott, 1999) and using a wide variety of feeding strategies (Shane, 1990). In the GOM, bottlenose dolphins often feed in association with shrimp trawlers (Fertl and Leatherwood, 1997). In addition to the use of active echolocation to find food, bottlenose dolphins likely detect and orient to fish prey by listening for the sounds prey produce—so-called `passive listening' (Barros and Myrberg, 1987; Gannon et al., 2005). Nearshore bottlenose dolphins prey predominately on coastal fish and cephalopods, while offshore individuals prey on pelagic cephalopods and a large variety of epi- and mesopelagic fish species (Van Waerebeek et al., 1990; Mead and Potter, 1995).
NMFS recognizes several stocks of bottlenose dolphins in the GOM, including a northern oceanic stock; a continental shelf and slope stock; western, northern, and eastern coastal stocks; and a group of 32 bay, sound, and estuarine stocks (Blaylock et al., 1995; Waring et al., 2006). Bottlenose dolphins likely occur within both offshore and nearshore waters of the project area. Bottlenose dolphins present in the project area would likely be represented by individuals from the eastern coastal stock and the relevant bay, sound, and estuarine stocks.
Bottlenose dolphins along the U.S. coastline are believed to be organized into local populations, or stocks, each occupying a small region of coast with some migration to and from inshore and offshore waters (Schmidly, 1981). The seaward boundary for coastal stocks, the 20-m (66-ft) isobath, generally corresponds to survey strata (Scott, 1990; Blaylock and Hoggard, 1994; Fulling et al., 2003) and represents a management boundary rather than an ecological boundary. Both “coastal/nearshore” and “offshore” ecotypes of bottlenose dolphins (Hersh and Duffield, 1990) occur in the GOM (LeDuc and Curry, 1998), and both could potentially occur in coastal waters. The best abundance estimate available for the northern GOM eastern coastal stock of bottlenose dolphins is 7,702, with a minimum population estimate of 6,551. The status of the eastern coastal stock relative to optimum sustainable population (OSP) level is not known and population trends cannot be determined due to insufficient data. The eastern coastal stock is not considered a strategic stock under the MMPA because the stock's average annual human-related mortality and serious injury does not exceed potential biological removal (PBR) (Waring et al., 2010).
Bottlenose dolphins are distributed throughout the bays, sounds and estuaries of the GOM (Mullin, 1988). The identification of biologically-meaningful “stocks” of bottlenose dolphins in these waters is complicated by the high degree of behavioral variability exhibited by this species (Shane et al., 1986; Wells and Scott, 1999; Wells, 2003), and by the lack of requisite information for much of the region. However, distinct stocks are provisionally identified in each of 32 areas of contiguous, enclosed or semi-enclosed bodies of water adjacent to the northern GOM. Bay, sound, and estuarine dolphins found in the project area would likely be from Tampa Bay or Sarasota Bay.
These “communities” include resident dolphins that regularly share large portions of their ranges, exhibit similar distinct genetic profiles, and interact with each other to a much greater extent than with dolphins in adjacent waters. While these communities do not constitute closed demographic populations, the geographic nature of these areas and long-term, multi-generational stability of residency patterns suggest that they may exist as discrete, functioning units of their ecosystems. Members of these stocks emphasize use of the bay, sound, or estuary waters, with limited movements through passes to the GOM (Shane, 1977, 1990; Gruber, 1981; Irvine et al., 1981; Maze and Würsig, 1999; Lynn and Würsig, 2002; Fazioli et al., 2006). These habitat use patterns are reflected in the ecology of the dolphins in some areas; for example, residents of Sarasota Bay, Florida, lack squid in their diet, unlike non-resident dolphins found stranded on nearby Gulf beaches (Barros and Wells, 1998).
Genetic exchange occurs between resident communities; hence the application of the demographically and behaviorally-based term “community” rather than “population” (Wells, 1986a; Sellas et al., 2005). A variety of potential exchange mechanisms occur in the Gulf. Small numbers of inshore dolphins traveling between regions have been reported, with patterns ranging from traveling through adjacent communities (Wells, 1986b; Wells et al., 1996a,b) to movements over distances of several hundred kilometers in Texas waters (Gruber, 1981; Lynn and Würsig, 2002). In many areas, year-round residents co-occur with non-resident dolphins, providing potential opportunities for genetic exchange. Non-residents exhibit a variety of patterns, ranging from apparent nomadism recorded as transience to apparent seasonal or non-seasonal migrations. Passes, especially the mouths of the larger estuaries, serve as mixing areas. For example, several communities mix at the mouth of Tampa Bay (Wells, 1986a). Seasonal movements of dolphins into and out of some of the bays, sounds and estuaries provide additional opportunities for genetic exchange with residents, and complicate the identification of stocks in coastal and inshore waters.
In larger bay systems (e.g., Tampa Bay), seasonal changes in abundance suggest possible migrations, and fall/winter increases in abundance have been noted for Tampa Bay (Scott et al., 1989). A number of geographically and socially distinct subgroupings of dolphins in some regions, including Tampa Bay, have been identified, but the importance of these distinctions to stock designations remains undetermined. For Tampa Bay, Urian et al. (2009) recently described fine-scale population structuring into five discrete communities (including the adjacent Sarasota Bay community) that differed in their social interactions and ranging patterns. Structure was found despite a lack of physiographic barriers to movement within this large, open embayment.
In the vicinity of the action area, there are distinct geographic subdivisions with year-round resident animals from Tampa Bay, Sarasota Bay, and Charlotte Harbor as well as a seasonal coastal stock (discussed previously; 1 to 12 km [0.6-7.5 mi] offshore) with mixing on a limited basis (Wells et al., 1996; Wells and Scott, 2002; Sellas et al., 2005). The Sarasota community's range extends from southern Tampa Bay southward through Sarasota Bay, and into the GOM about 1 km offshore. Waring et al. (2010) identified the animals in Tampa Bay as having a best estimate of abundance of 559 individuals (based on 1994 data) and those in Sarasota Bay as having a best abundance estimate of 160 individuals (based on 2007 data). The status of the stock relative to OSP is unknown. Because most of the stock sizes are currently unknown, but likely small, and relatively few mortalities or serious injuries would exceed PBR, NMFS considers that each of these stocks is a strategic stock under the MMPA (Waring et al., 2010).
Atlantic spotted dolphins—Atlantic spotted dolphins are widely distributed in warm temperate and tropical waters of the Atlantic Ocean, including the GOM (Waring et al., 2006). In the northern Gulf, these animals occur mainly on the continental shelf (Jefferson and Schiro, 1997). During GulfCet II aerial and shipboard surveys in the northern GOM, Atlantic spotted dolphins were seen at water depths ranging from 22 to 222 m (72-728 ft) (Mullin and Hoggard, 2000). On the shelf, they were second in abundance to bottlenose dolphins. Atlantic spotted dolphins can be expected to occur on the continental shelf during all seasons. However, they may be more common during spring (Jefferson and Schiro, 1997; Mullin and Hoggard, 2000). It is expected that Atlantic spotted dolphins could occur within offshore waters of the project area.
Atlantic spotted dolphins in the northern GOM are abundant in continental shelf waters from between 10 and 200 m (33 to 656 ft) to slope waters < 500 m (1,640 ft) (Fulling et al. 2003; Mullin and Fulling, 2003a). Griffin and Griffin (2003) reported that on the west Florida Shelf they are more common in waters from 20 to 180 m (66 to 591 ft), while Mullin et al. (2004) found that Atlantic spotted dolphins were sighted in waters with a bottom depth typically < 300 m (984 ft). Griffin and Griffin (2004) reported higher abundances of spotted dolphins on the west Florida Shelf between the months of November and May than during the rest of the year.
Atlantic spotted dolphins in the GOM have been seen feeding cooperatively on clupeid fishes (e.g., herring, sardine) and are known to feed in association with shrimp trawlers (Fertl and Würsig, 1995; Fertl and Leatherwood, 1997, respectively). In the Bahamas, this species has been observed to chase and catch flying fish (MacLeod et al., 2004). The only information on dive depth for this species is based on a satellite-tagged individual from the GOM (Davis et al., 1996). This individual made short, shallow dives (more than 76 percent of the time to depths < 10 m) over the continental shelf, although some dives were as deep as 40 to 60 m (Davis et al., 1996).
The GOM population is considered a separate stock for management purposes. The most recent abundance estimate for Atlantic spotted dolphin in the GOM, based on pooled survey data from 2000 and 2001, was 37,611 (Waring et al., 2009). These animals were found entirely in OCS waters; the abundance estimate for oceanic waters, from surveys conducted in 2003-04, was zero. There is insufficient information for this stock to determine PBR or its status relative to OSP. Despite an undetermined PBR and unknown population size, the GOM stock is not considered a strategic stock