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Brian B Hatfield
Brian Hatfield has been involved with sea otter research since the late 1970s and has been employed with USGS (migrating from USFWS and NBS) since the mid-1980s. Currently, he coordinates the range-wide sea otter surveys in California, including those at San Nicolas Island, and co-coordinates the sea otter stranding network. Brian maintains rebreather diving certification in order to capture sea otters for tagging and sample collection. He has participated in sea otter research in the Commander and Aleutian Islands, Prince William Sound, SE Alaska, Vancouver Island, Washington, as well as California. His current interests include the increasing shark bite-caused sea otter mortality, sea otter-fisheries interactions, recolonization of the California Islands by sea otters and the colonization of the Point Piedras Blancas, California, area by northern elephant seals.
MSc, Biology, California Polytechnic State University San Luis Obispo, 1979
BA, Biology (with honors), University of California Santa Cruz, 1975
Science and Products
The California Sea Otter Stranding Network is part of the USGS effort to monitor southern sea otters (Enhydra lutris nereis) and provide data to the U.S. Fish and Wildlife Service. WERC's sea otter team works with multiple institutions and partners to report, recover, and examine stranded sea otters. In addition, instructions on how to report a stranded sea otter are included in this webpage...
WERC colloborates with other research scientists to conduct annual population surveys of the southern sea otter -- a federally listed threatened species. In coordination with the California Department of Fish and Game and other institutions, ongoing surveys and research continues to inform the southern sea otter recovery plan for the U.S. Fish and Wildlife Service, and contributes to our...
WERC's sea otter researchers are developing and utilizing a variety of methodological and analytical tools to understand the causes of biological and ecological trends in sea otter populations, and to predict the ecological consequences of management practices on these populations and their ecosystems.
Sea otters are crucial indicators of the health of our nearshore waters and coastal resources, from kelp forests to fisheries. What clues does the sea otter's decline hold for our knowledge of ecosystem and global change? WERC's sea otter team and U.S. and Canadian researchers have teamed together to investigate.
Relevance to USGS Missions:
This research project has direct...
Scientists at the Santa Cruz Field Station study sea otters and seabirds in their environment. The USGS Western Ecological Research Center has two research missions based in the Santa Cruz region:
California sea otter (Enhydra lutris nereis) census results, spring 2018
The 2018 census of southern sea otters (Enhydra lutris nereis) was conducted from late April to mid-May along the mainland coast of central California and in April at San Nicolas Island in southern California. The 3-year average of combined counts from the mainland range and San Nicolas Island was 3,128, a decrease of 58 sea otters from the...Hatfield, Brian B.; Yee, Julie L.; Kenner, Michael C.; Tomoleoni, Joseph A.; Tinker, M. Tim
California sea otter (Enhydra lutris nereis) census results, Spring 2017
The 2017 census of southern sea otters (Enhydra lutris nereis) was conducted between late April and early July along the mainland coast of central California and in April at San Nicolas Island in southern California. The 3-year average of combined counts from the mainland range and San Nicolas Island was 3,186, down by 86 sea otters from the...Tinker, M. Tim; Hatfield, Brian B.
California sea otter (Enhydra lutris nereis) census results, Spring 2016
The 2016 census of southern sea otters Enhydra lutris nereis was conducted in May along the mainland coast of central California and in April at San Nicolas Island in southern California. The 3-year average of combined counts from the mainland range and San Nicolas Island was 3,272. This is the first year that the official index has exceeded...Tinker, M. Tim; Hatfield, Brian B.
Dramatic increase in sea otter mortality from white sharks in California
Although southern sea otters (Enhydra lutris nereis) are not considered prey for white sharks (Carcharodon carcharias), sharks do nonetheless bite sea otters. We analyzed spatial and temporal trends in shark bites on sea otters in California, assessing the frequency of shark bite wounds in 1,870 carcasses collected since 1985. The proportion of...Tinker, M. Tim; Hatfield, Brian B.; Harris, Michael D.; Ames, Jack A.
A multi-decade time series of kelp forest community structure at San Nicolas Island, California
San Nicolas Island is surrounded by broad areas of shallow subtidal habitat, characterized by dynamic kelp forest communities that undergo dramatic and abrupt shifts in community composition. Although these reefs are fished, the physical isolation of the island means that they receive less impact from human activities than most reefs in Southern...Lafferty, Kevin D.; Kenner, Michael C.; Estes, James A.; Tinker, M. Tim; Bodkin, James L.; Cowen, Robert K.; Harrold, Christopher; Novak, Mark; Rassweiler, Andrew; Reed, Daniel C.
Sea otter mortality in fish and shellfish traps: Estimating potential impacts and exploring possible solutions
Sea otters Enhydra lutris can be bycaught and drowned in fishing pots and traps, which may pose a threat to the welfare of otter populations. We explored this potential problem and its solutions using a wide variety of analyses. We exposed live California (USA) sea otters to finfish traps, lobster traps, and mock Dungeness crab traps in captive...Hatfield, B.B.; Ames, J.A.; Estes, J.A.; Tinker, M.T.; Johnson, A.B.; Staedler, M.M.; Harris, M.D.
Incorporating diverse data and realistic complexity into demographic estimation procedures for sea otters
Reliable information on historical and current population dynamics is central to understanding patterns of growth and decline in animal populations. We developed a maximum likelihood-based analysis to estimate spatial and temporal trends in age/sex-specific survival rates for the threatened southern sea otter (Enhydra lutris nereis), using annual...Tinker, M. Timothy; Doak, Daniel F.; Estes, James A.; Hatfield, Brian B.; Staedler, Michelle M.; Gross, Arthur
Spatial and temporal variation in sea otter demography
1) Better information on historical and current population dynamics is central to understanding patterns of growth and decline in the California sea otter population. We developed a maximum likelihood-based analytical method to estimate historical age/sex specific vital rates as well as spatial and temporal variation in vital rates from...Tinker, M. Tim; Estes, James A.; Ralls, Katherine; Williams, Terrie M.; Jessup, David A.; Costa, Daniel P.; Tinker, M. Tim; Doak, Daniel F.; Estes, James A.; Hatfield, Brian B.; Steadler, Michelle M.; Bodkin, James L.
Causes of mortality in California sea otters during periods of population growth and decline
Elevated mortality appears to be the main reason for both sluggish growth and periods of decline in the threatened California sea otter population. We assessed causes of mortality from salvage records of 3,105 beach-cast carcasses recovered from 1968 through 1999, contrasting two periods of growth with two periods of decline. Overall, an estimated...Estes, J.A.; Hatfield, B.B.; Ralls, K.; Ames, J.
Status of translocated sea otters at San Nicolas Island, California
In the 1970s about 1,650 southern sea otters (Enhydra lutris nereis) were restricted to the central California coast (Riedman and Estes, 1990), and a high volume of oil was being shipped through the region. Because of the vulnerability of sea otters to contamination from oil (Costa and Kooyman, 1982; Williams and Davis, 1995) that would likely...Rathbun, Galen B.; Hatfield, Brian B.; Murphey, Thomas G.
Interactions between northern elephant seals and vehicles near Point Piedras Blancas, CaliforniaHatfield, B.B.; Rathbun, G.B.
Foraging patterns of California sea otters as indicated by telemetry
Foraging behavior was studied in 38 sea otters (Enhydra lutris) implanted with radio transmitters. The observed foraging behavior of instrumented individuals was similar to that of uninstrumented otters observed in previous studies: dive duration varied with prey type but not with prey size, dive success was highest for small prey, and the length...Ralls, Katherine; Hatfield, Brian B.; Siniff, Donald B.
In the future of wildlife tracking, sea otters have their own social network.