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Brian B. Hatfield

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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 population censuses and the age structure of salvaged carcass collections. We evaluated a wide range of possible spatial and temporal effects and used model averaging to incorporate model uncertainty into the resulting estimates of key vital rates and their variances. We compared these results to current demographic parameters estimated in a telemetry-based study conducted...
Categories: Publication; Types: Citation; Tags: Ecological Applications
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This dataset represents an archived record of annual California sea otter surveys from 1985-2014. Survey procedures involve counting animals during the "spring survey" -- generally beginning in late April or early May and usually ending in late May early June but may extend into early July, depending on weather conditions. Annual surveys are organized by survey year and within each year, three shapefiles are included: census summary of southern sea otter, extra limit counts of southern sea otter, and range extent of southern sea otter. The surveys, conducted cooperatively by scientists of the U.S. Geological Survey, California Department of Fish and Wildlife, U.S. Fish and Wildlife Service and Monterey Bay Aquarium...
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The spring 2017 mainland sea otter count began on April 30, and although the shore-based counts were completed by May 12, 2017, the aerial counts were not completed until July 12, 2017. Overall viewing conditions this year were good, although not as good as conditions experienced during the 2016 spring census (View Score 2.4 versus 3.1, where 0=poor, 1=fair, 2=good, 3=very good, and 4=excellent). The surface canopies of kelp (Macrocystis sp.) were considered by most participants to be considerably below normal for this time of year in most areas of the mainland range. Sea otters along the mainland coast were surveyed from Pillar Point in San Mateo County in the north to Rincon Point in the south at the Santa Barbara/Ventura...
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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 stranded sea otters having shark bites has increased sharply since 2003, and white shark bites now account for >50% of recovered carcasses. The trend was most pronounced in the southern part of the range, from Estero Bay to Point Conception, where shark bite frequency has increased eightfold. Seasonal trends were also evident: most shark-bitten carcasses are recovered in...
Categories: Publication; Types: Citation; Tags: Marine Mammal Science
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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 longitudinal databases on population census numbers and the age-structure of salvaged carcasses.2) We estimated current demographic parameters by conducting a mark-recapture study, measuring survival and reproduction of 115 radio-tagged individuals between 2001 and 2004. These current estimates were compared to estimates from a similar study of radiotagged otters conducted in the...
Categories: Publication; Types: Citation
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