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Marine Mammal Protection Act; Stock Assessment Report for the Southern Sea Otter in California

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Fish and Wildlife Service, Interior.


Notice of availability; request for comments.


In accordance with the Marine Mammal Protection Act of 1972, as amended, we, the U.S. Fish and Wildlife Service, have developed a draft revised marine mammal stock assessment report for the southern sea otter stock in the State of California. We now make the draft stock assessment report available for public review and comment.


We will consider comments that are received or postmarked on or before April 27, 2020.


Document availability: If you wish to review the draft revised stock assessment report for southern sea otter, you may obtain a copy from our website at​ventura. Alternatively, you may contact the Ventura Fish and Wildlife Office, 2493 Portola Road, Suite B, Ventura, CA 93003 (telephone: 805-644-1766).

Comment submission: If you wish to comment on the draft stock assessment report, you may submit your comments in writing by any one of the following methods:

  • U.S. mail: Field Supervisor, at the above address;
  • Hand delivery: Ventura Fish and Wildlife Office at the above address;
  • Fax: 805-644-3958; or
  • Email:
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Lilian Carswell, at the above street address, by telephone (805-677-3325), or by email ( Persons who use a telecommunications device for the deaf (TDD) may call the Federal Relay Service at 800-877-8339.

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We announce the availability for review and comment of a draft revised marine mammal stock assessment report (SAR) for the southern sea otter (Enhydra lutris nereis) stock in the State of California.


Under the Marine Mammal Protection Act of 1972, as amended (MMPA; 16 U.S.C. 1361 et seq.), and its implementing regulations in the Code of Federal Regulations (CFR) at 50 CFR part 18, the U.S. Fish and Wildlife Service (Service) regulates the taking; import; and, under certain conditions, possession; transportation; purchasing; selling; and offering for sale, purchase, or export, of marine mammals. One of the MMPA's goals is to ensure that stocks of marine mammals occurring in waters under U.S. jurisdiction do not experience a level of human-caused mortality and serious injury that is likely to cause the stock to be reduced below its optimum sustainable population level (OSP). OSP is defined under the MMPA as “the number of animals which will result in the maximum productivity of the population or the species, keeping in mind the carrying capacity of the habitat and the health of the ecosystem of which they form a constituent element” (16 U.S.C. 1362(9)).

To help accomplish the goal of maintaining marine mammal stocks at their OSPs, section 117 of the MMPA requires the Service and the National Marine Fisheries Service (NMFS) to prepare a SAR for each marine mammal stock that occurs in waters under U.S. jurisdiction. A SAR must be based on the best scientific information available; therefore, we prepare it in consultation with regional scientific review groups established under section 117(d) of the MMPA. Each SAR must include:

1. A description of the stock and its geographic range;

2. A minimum population estimate, current and maximum net productivity rate, and current population trend;

3. An estimate of the annual human-caused mortality and serious injury by source and, for a strategic stock, other factors that may be causing a decline or impeding recovery;

4. A description of commercial fishery interactions;

5. A categorization of the status of the stock; and

6. An estimate of the potential biological removal (PBR) level.

The MMPA defines the PBR as “the maximum number of animals, not including natural mortalities, that may be removed from a marine mammal stock while allowing that stock to reach or maintain its OSP” (16 U.S.C. 1362(20)). The PBR is the product of the minimum population estimate of the stock (Nmin); one-half the maximum theoretical or estimated net productivity rate of the stock at a small population size (Rmax); and a recovery factor (Fr) of between 0.1 and 1.0, which is intended to compensate for uncertainty and unknown estimation errors. This can be written as:

PBR = (Nmin)(1/2 of the Rmax)(Fr)

Section 117 of the MMPA also requires the Service and NMFS to review the SARs (a) at least annually for stocks that are specified as strategic stocks, (b) at least annually for stocks for which significant new information is available, and (c) at least once every 3 years for all other stocks. If our review of the status of a stock indicates that it has changed or may be more accurately determined, then the SAR must be revised accordingly.

A strategic stock is defined in the MMPA as a marine mammal stock “(a) for which the level of direct human-caused mortality exceeds the PBR level; (b) which, based on the best available scientific information, is declining and is likely to be listed as a threatened species under the Endangered Species Act of 1973, as amended (16 U.S.C. 1531 et seq.) [the “ESA”], within the foreseeable future; or (c) which is listed as a threatened or endangered species under the ESA, or is designated as depleted under [the MMPA].” 16 U.S.C. 1362(19).

Stock Assessment Report History for the Southern Sea Otter in California

The southern sea otter SAR was last revised in 2017. Because the southern sea otter is listed as a threatened species under the ESA, the stock is considered strategic. Therefore, the Service reviews the stock assessment annually. In 2018, Service review concluded that revision was not warranted because the status of the stock had not changed, nor could it be more accurately determined. However, upon review in 2019, the Service determined that revision was warranted because the status of the stock may be subject to change. The range-wide population index (i.e., population level over a consecutive 3-year period) reached the ESA threshold (i.e., exceeding 3,090 animals) for delisting consideration identified in the Southern Sea Otter Recovery Plan (U.S. Fish and Wildlife Service 2003). As a result, the Service will initiate an ESA status review to determine whether delisting of the southern sea otter is appropriate, which could result in a Start Printed Page 4697change to the status of the stock under the MMPA.

Summary of Draft Revised Stock Assessment Report for the Southern Sea Otter in California

The following table summarizes some of the information contained in the draft revised southern sea otter SAR, which includes the stock's Nmin, Rmax, Fr, PBR, annual estimated human-caused mortality and serious injury, and status. After consideration of any public comments we receive, the Service will revise and finalize the SAR, as appropriate. We will publish a notice of availability and summary of the final SAR, including responses to submitted comments.

Summary—Draft Revised Stock Assessment Report, Southern Sea Otter in California

Southern sea otter stockNMINRMAXFRPBRAnnual estimated human-caused mortality and serious injuryStock status
Mainland2,9860.060.19.24Figures by specific source, where known, are provided in the SARStrategic.
San Nicolas Island950.130.10.62

Public Availability of Comments

Before including your address, phone number, email address, or other personal identifying information in your comment, you should be aware that your entire comment—including your personal identifying information—may be made publicly available at any time. While you can ask us in your comment to withhold your personal identifying information from public review, we cannot guarantee that we will be able to do so.


In accordance with the MMPA, we include in this notice a list of the information sources and public reports upon which we based the SAR:

Babcock, E.A., E.K. Pikitch, and C.G. Hudon. 2003. How much observer coverage is enough to adequately estimate bycatch? Pew Institute for Ocean Science and Oceana, 36 pp.

Bacon, C.E. 1994. An ecotoxicological comparison of organic contaminants in sea otters among populations in California and Alaska. M.S. thesis, University of California, Santa Cruz.

Bacon, C.E., W.M. Jarman, J.A. Estes, M. Simon, and R.J. Norstrom. 1999. Comparison of organochlorine contaminants among sea otter (Enhydra lutris) populations in California and Alaska. Environ. Toxicology and Chemistry 18:452-458.

Barlow, J. 1989. Estimating sample size required to monitor marine mammal mortality in California gillnet fisheries. Southwest Fisheries Science Center Administrative Report LJ-89-08, 8 pp.

Bentall, G.B. 2005. Morphological and behavioral correlates of population status in the southern sea otter: A comparative study between central California and San Nicolas Island. Master's Thesis, University of California, Santa Cruz, CA, unpublished.

Burge, C.A., C.M. Eakin, C.S. Friedman, B. Froelich, P.K. Hershberger, E.E. Hofmann, L.E. Petes, K.C. Prager, E. Weil, B.L. Willis, SE Ford, and C.D. Harvell. 2014. Climate change influences on marine infectious diseases: Implications for management and society. Annual Review of Marine Science 6:249-277.

Bryant, H.C. 1915. Sea otters near Point Sur. California Department of Fish and Game Bulletin. 1:134-135.

Cameron, G.A. and K.A. Forney. 2000. Preliminary estimates of cetacean mortality in California/Oregon gillnet fisheries for 1999. Paper SC/S2/O24 presented to the International Whaling Commission, 2000 (unpublished), 12 pp. Available from NMFS, Southwest Fisheries Science Center, P.O. Box 271, La Jolla, CA 92038.

Carretta, J.V. 2001. Preliminary estimates of cetacean mortality in California gillnet fisheries for 2000. Paper SC/53/SM9 presented to the International Whaling Commission, 2001 (unpublished), 21 pp. Available from NMFS, Southwest Fisheries Science Center, P.O. Box 271, La Jolla, CA 92038.

Chinn, S.M., M.A. Miller, M.T. Tinker, M.M. Staedler, F.I. Batac, E.M. Dodd, L.A. Henkel. 2016. The high cost of motherhood: End-lactation syndrome in southern sea otters. Journal of Wildlife Diseases 52:307-318. doi: 10.7589/2015-06-158.

Conrad, P.A., M.A. Miller, C. Kreuder, E.R. James, J. Mazet, H. Dabritz, D.A. Jessup, F. Gulland, M.E. Grigg. 2005. Transmission of toxoplasma: Clues from the study of sea otters as sentinels of Toxoplasma gondii flow into the marine environment. International Journal for Parasitology 35:1155-1168.

Cronin, M.A., J. Bodkin, B. Bellachey, J.A. Estes, and J.C. Patton. 1996. Mitochondrial-DNA variation among subspecies and populations of sea otters (Enhydra lutris). Journal of Mammalogy 77:546-557.

Dubey, J.P., N.L. Miller, and D.K. Frenkel. 1970. Toxoplasma gondii life cycle in cats. Journal of the American Veterinary Medical Association 157:1767-1770.

Estes, J.A. 1990. Growth and equilibrium in sea otter populations. J. Anim. Ecol. 59:385-401.

Estes, J.A. and R.J. Jameson. 1988. A double-survey estimate for sighting probability of sea otters in California. Journal of Wildlife Management 52:70-76.

Estes, J.A., B.B. Hatfield, K. Ralls, and J. Ames. 2003. Causes of mortality in California sea otters during periods of population growth and decline. Marine Mammal Science 19:198-216.

Forney, K.A., S.R. Benson, and G.A. Cameron. 2001. Central California gill net effort and bycatch of sensitive species, 1990-1998. Pages 141-160 in Seabird Bycatch: Trends, Roadblocks, and Solutions, E.F. Melvin and J.K. Parrish, eds. Proceedings of an International Symposium of the Pacific Seabird Group, University of Alaska Sea Grant, Fairbanks, Alaska, 212 pp.

Gazeau, F., L.M. Parker, S. Comeau, J.-P. Gattuso, W.A. O'Connor, S. Martin, H.-O. Pörtner, and P.M. Ross. 2013. Impacts of ocean acidification on marine shelled molluscs. Marine Biology 160:2207-2245.

Gerber, L.R., M.T. Tinker, D.F. Doak, J.A. Estes, and D.A. Jessup. 2004. Mortality sensitivity in life-stage simulation analysis: A case study of southern sea otters. Ecological Applications 14:1554-1565.

Hatfield, B.B. and J.A. Estes. 2000. Preliminary results of an evaluation of the potential threat to sea otters posed by the nearshore finfish trap fishery. Unpublished, 6 pp. + appendices.

Hatfield, B.B., J.L. Yee, M.C. Kenner, J.A. Tomoleoni, and M.T. Tinker. 2018. California sea otter (Enhydra lutris nereis) census results, spring 2018. U.S. Geological Survey Data Series 1097. 10 pp.​10.3133/​ds1097.

Hatfield, B.B., J.A. Ames, J.A. Estes, M.T. Tinker, A.B. Johnson, M.M. Staedler, and M.D. Harris. 2011. Sea otter mortality in fish and shellfish traps: Estimating potential impacts and exploring possible solutions. Endangered Species Research 13:219-229.

Herrick, S.F. Jr. and D. Hanan. 1988. A review of California entangling net fisheries, 1981-1986. National Oceanic and Atmospheric Administration Technical Memorandum. National Marine Fisheries Service. NOAA-TM-NMFS-SWFC-108, 39 pp.

Jameson, R.J. 1989. Movements, home range, Start Printed Page 4698and territories of male sea otters off central California. Marine Mammal Science 5:159-172.

Jameson, R.J. and S. Jeffries. 1999. Results of the 1999 survey of the Washington sea otter population. Unpublished report, 5 pp.

Jameson, R.J. and S. Jeffries. 2005. Results of the 2005 survey of the reintroduced Washington sea otter population. Unpublished report, 6 pp.

Jessup D.A., M.A. Miller, M. Harris, B.B. Hatfield, and J.A. Estes. 2004. The 2003 southern sea otter (Enhydra lutris nereis) unusual mortality event: A preliminary report to NOAA and USFWS. Unpublished report, 38 pp.

Johnson, C.K., M.T. Tinker, J.A. Estes, P.A. Conrad, M. Staedler, M.A. Miller, D.A. Jessup and J.A.K. Mazet. 2009. Prey choice and habitat use drive sea otter pathogen exposure in a resource-limited coastal system. PNAS 106:2242-2247.

Kannan, K., E. Perrotta, and N.J. Thomas. 2006. Association between perfluorinated compounds and pathological conditions in southern sea otters. Environmental Science & Technology 40:4943-4948.

Kannan, K., E. Perrotta, N.J. Thomas, and K.M. Aldous. 2007. A comparative analysis of polybrominated diphenyl ethers and polychlorinated biphenyls in southern sea otters that died of infectious diseases and noninfectious causes. Archives of Environmental Contamination and Toxicology 53:293-302.

Kannan K., K.S. Guruge, N.J. Thomas, S. Tanabe, J.P. Giesy. 1998. Butyltin residues in southern sea otters (Enhydra lutris nereis) found dead along California coastal waters. Environmental Science and Technology 32:1169-1175.

Kooyman, G.L. and D.P. Costa. 1979. Effects of oiling on temperature regulation in sea otters. Yearly progress report, Outer Continental Shelf Energy Assessment Program.

Kreuder, C., M.A. Miller, D.A. Jessup, L.J. Lowenstein, M.D. Harris, J.A. Ames, T.E. Carpenter, P.A. Conrad, and J.A.K. Mazet. 2003. Patterns of mortality in southern sea otters (Enhydra lutris nereis) from 1998-2001. Journal of Wildlife Diseases 39:495-509.

Kreuder, C., M.A. Miller, L.J. Lowenstine, P.A. Conrad, T.E. Carpenter, D.A. Jessup, and J.A.K. Mazet. 2005. Evaluation of cardiac lesions and risk factors associated with myocarditis and dilated cardiomyopathy in southern sea otters (Enhydra lutris nereis). American Journal of Veterinary Research 66:289-299.

Kroeker, K.J., R.L. Kordas, R.N. Crim, and G.G. Singh. 2010. Meta-analysis reveals negative yet variable effects of ocean acidification on marine organisms. Ecology Letters 13:1419-1434.

Kudela, R.M., J.Q. Lane, W.P. Cochlan. 2008. The potential role of anthropogenically derived nitrogen in the growth of harmful algae in California, USA. Harmful Algae 8:103-110.

Kurihara, H. and Y. Shirayama. 2004. Effects of increased atmospheric CO2 on sea urchin early development. Marine Ecology Progress Series 274:161-169.

Kurihara, H., T. Asai, S. Kato, and A. Ishimatsu. 2008. Effects of elevated pCO2 on early development in the mussel Mytilus galloprovincialis. Aquatic Biology 4:225-233.

Lafferty, K.D. and M.T. Tinker. 2014. Sea otters are recolonizing southern California in fits and starts. Ecosphere 5:50.​10.1890/​ES13-00394.1.

Laidre, K.L., R.J. Jameson, and D.P. DeMaster. 2001. An estimation of carrying capacity for sea otters along the California coast. Marine Mammal Science 17:294-309.

Larson, S., R. Jameson, J. Bodkin, M. Staedler, and P. Bentzen. 2002. Microsatellite DNA and mitochondrial DNA variation in remnant and translocated sea otter (Enhydra lutris) populations. Journal of Mammalogy 83:893-906.

Mayer, K.A., M.D. Dailey, and M.A. Miller. 2003. Helminth parasites of the southern sea otter Enhydra lutris nereis in central California: Abundance, distribution, and pathology. Diseases of Aquatic Organisms 53:77-88.

Miller, M.A., M.E. Grigg, C. Kreuder, E.R. James, A.C. Melli, P.R. Crosbie, D.A. Jessup, J.C. Boothroyd, D. Brownstein, and P.A. Conrad. 2004. An unusual genotype of Toxoplasma gondii is common in California sea otters (Enhydra lutris nereis) and is a cause of mortality. International Journal for Parasitology 34:275-284.

Miller, M.A., I.A. Gardner, C. Kreuder, D.M. Paradies, K.R. Worcester, D.A. Jessup, E. Dodd, M.D. Harris, J.A. Ames, A.E. Packham, and P.A. Conrad. 2002. Coastal freshwater runoff is a risk factor for Toxoplasma gondii infection of southern sea otters (Enhydra lutris nereis). International Journal for Parasitology 32:997-1006.

Miller, M.A., W.A. Miller, P.A. Conrad, E.R. James, A.C. Melli, C.M. Leutenegger, H.A. Dabritz, A.E. Packham, D. Paradies, M. Harris, J. Ames, D.A. Jessup, K. Worcester, M.E. Grigg. 2008. Type X Toxoplasma gondii in a wild mussel and terrestrial carnivores from coastal California: New linkages between terrestrial mammals, runoff and toxoplasmosis of sea otters. International Journal for Parasitology 38:1319-1328.

Miller, M.A., R.M. Kudela, A. Mekebri, D. Crane, S.C. Oates, M.T. Tinker, M. Staedler, W.A. Miller, S. Toy-Choutka, C. Domink, D. Hardin, G. Langlois, M. Murray, K. Ward and D.A. Jessup. 2010. Evidence for a novel marine harmful algal bloom: Cyanotoxin (Microcystin) transfer from land to sea otters. PLoS ONE 5:e12576.

Monson, D.H., J.A. Estes, J.L. Bodkin, and D.B. Siniff. 2000. Life history plasticity and population regulation in sea otters. Oikos 90:457-468.

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Nakata, H., K. Kannan, L. Jing, N. Thomas, S. Tanabe, and J.P. Giesy. 1998. Accumulation pattern of organochlorine pesticides and polychlorinated biphenyls in southern sea otters (Enhydra lutris nereis) found stranded along coastal California, USA. Environmental Pollution 103:45-53.

Ralls, K., T.C. Eagle, and D.B. Siniff. 1996. Movement and spatial use patterns of California sea otters. Canadian Journal of Zoology 74:1841-1849.

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Tinker, M.T., D.F. Doak, and J.A. Estes. 2008b. Using demography and movement behavior to predict range expansion of the southern sea otter. Ecological Applications 18:1781-1794.

Tinker, M.T., B.B. Hatfield, M.D. Harris, and J.A. Ames. 2016. Dramatic increase in sea otter mortality from white sharks in California. Marine Mammal Science 32:309-326.

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The authority for this action is the Marine Mammal Protection Act of 1972, as amended (16 U.S.C. 1361 et al.)

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Dated: January 8, 2020.

Aurelia Skipwith,

Director, U.S. Fish and Wildlife Service.

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[FR Doc. 2020-01326 Filed 1-24-20; 8:45 am]