Southern sea otter (Enhydra lutris nereis) population biology at Big Sur and Monterey, California --Investigating the consequences of resource abundance and anthropogenic stressors for sea otter recovery

Tinker, M. Tim; Tomoleoni, Joseph A.; Weitzman, Benjamin P.; Staedler, Michelle M.; Jessup, Dave; Murray, Michael J.; Miller, Melissa A.; Burgess, Tristan L.; Bowen, Lizabeth; Miles, A. Keith; Thometz, Nicole M.; Tarjan, L. Max; Golson, Emily A.; Batac, Francesca; Dodd, Erin; Berberich, Eva; Kunz, Jessica; Bentall, Gena B.; Fujii, Jessica A.; Nicholson, Teri E.; Newsome, Seth D.; Melli, Ann C.; LaRoche, Nicole L.; MacCormick, Holly A.; Johnson, Andrew; Henkel, Laird A.; Kreuder-Johnson, Chris; Conrad, Pat

doi:10.3133/ofr20191022

Cited by 32 publications

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“…2B, 3; Supplementary material Appendix 1 Table A5). Individuals within this core part of the range devote nearly half their daily activity to foraging (Tinker et al 2008a(Tinker et al , 2013), demonstrate lower foraging success, and exhibit poorer body condition and survival rates . Adult females in particular are extremely vulnerable to mortality during periods of increased energetic demands (Ralls and Siniff 1990, Thometz et al 2014, Chinn et al 2016.…”

Section: Discussionmentioning

confidence: 99%

“…1D), providing ideal shelter and prey habitat for sea otters (Mann 1982, Duggins 1988, Riedman and Estes 1990. Sea otters within this core region have been at high density for decades and are approaching carrying capacity (Tinker et al 2006(Tinker et al , 2008a(Tinker et al , 2013. Regions adjacent to this core area, extending to the range peripheries, however, are characterized by large-scale soft and mixed (both sandy and rocky sediment) subtidal habitats that represent substantially poorer substrate for persistent kelp forests due to light-limiting turbidity, sedimentation, or scouring, especially in areas of high wave energy or exposure (North 1971, Foster 1982, Graham et al 2008, Foster et al 2013.…”

Section: Introductionmentioning

confidence: 99%

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Gaps in kelp cover may threaten the recovery of California sea otters

et al. 2018

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Despite more than a century of federal protection, the California sea otter Enhydra lutris nereis remains threatened under the U.S. Endangered Species Act (ESA), and the population has not appreciably expanded its range in two decades. Here, we examine a novel dataset of 725 sea otter live strandings from 1984-2015 to gain insights into demographic and environmental factors underlying threats to sea otter recovery. Using multinomial logistic regression to evaluate spatiotemporal patterns of stranding causes, we demonstrate that increases in stranding rates, particularly outside the range center, are related to a substantial increase in shark bites. By contrast, trauma linked to human activities has declined dramatically, and now accounts for less than 5% of stranding cases. Within the range core, where the sea otter population seems regulated by prey availability, symptoms of energetic stress represent more than 63% of all strandings and are strongly associated with high sea otter density. Conversely, in range peripheries, the majority of strandings are caused by shark bite and neurological disease. Notably, these threats are virtually absent where nearshore habitat is characterized by at least 10% kelp canopy cover. Our analyses reveal that declining kelp cover may therefore constrain the population's spatial expansion and recovery in two key ways. Absence of kelp intensifies density-independent threats in the range peripheries, and likely limits dispersal of reproductive females, which depend on kelp canopy for nursery habitat. These results highlight the significance of both top-down and bottomup processes in population dynamics, and inform an ecosystem-based approach to conservation planning.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Gaps in kelp cover may threaten the recovery of California sea otters

et al. 2018

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“…For SEAK as a whole and the three focal subregions, we summarized annual reported number of harvested sea otters, the age/sex class of harvested sea otters, and the annual harvest rate using the estimated preharvest population abundance for that year from Tinker et al. (, b; Eq. ).…”

Section: Methodsmentioning

confidence: 99%

“…We adopted the same subregions used by Tinker et al (2019a) to estimate carrying capacity of sea otters in SEAK. The authors delineated these subregions in order to track population trends in SEAK at an appropriate spatial scale based on sea otter life history and ecology and on recent findings of fine-scale demographic structuring of sea otter populations (Bodkin 2015, Tinker 2015, Gagne et al 2018, Johnson et al 2019, Tinker et al 2019b). Specifically, each subregion encompassed an area of sea otter habitat approximately 100 times the size of a typical adult home range, which ranges from 1.0 to 11.0 km 2 (Garshelis andGarshelis 1984, Tarjan and, bounded by the low tide line inshore and the 40 m depth contour offshore ( Fig.…”

Section: Study Areamentioning

confidence: 99%

Location‐specific factors influence patterns and effects of subsistence sea otter harvest in Southeast Alaska

et al. 2019

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To better understand the spatial context of population dynamics of sea otters (Enhydra lutris) in Southeast Alaska (SEAK), we investigated the spatial and temporal patterns of subsistence sea otter harvest and assessed the effect of harvest on population growth. U.S. federal law permits subsistence harvest of sea otters and sale of clothing and handicrafts made by coastal Alaska Natives. Hunters are required to self‐report these harvests along with information on date, location, age class, and sex. Using harvest data collected from 1988 to 2015, we developed a spatially explicit, age‐structured, density‐dependent population simulation model to explore the potential impacts of harvest on sea otter population dynamics. We examined patterns of harvest and simulation model results at two spatial scales: the SEAK stock and three smaller subregions that vary in sea otter occupation time and carrying capacity: Sitka Sound, Keku Strait, and the Maurelle Islands. Annual sea otter harvest in SEAK increased from 55 animals in 1988 to a reported maximum of 1449 animals in 2013. Estimated mean annual harvest rate was 2.8% at the SEAK stock scale, but ranged from 0% to 39.3% across the three focal subregions described above. Across all subregions (n = 55), annual sea otter harvest rate was strongly influenced by time since recolonization, sea otter population density, and proximity to communities with sea otter hunters. The simulation model predicted population trends and per capita harvest rates similar to those estimated from aerial survey data, providing a reasonable approximation of population dynamics. Results of the simulation model suggested that current harvest levels can reduce population size at both the SEAK and subregional scales. Variation in harvest impacts was a function of subregion‐specific factors, including time since recolonization and population status with respect to carrying capacity. We found that subsistence harvest and its population effects were scale‐ and location‐dependent, indicating that higher spatial and temporal resolution of sea otter population and hunting data could help address emerging sea otter management and conservation concerns in this region.

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“…Typical energy intake rates range from 12 kcal/min to 21 kcal/min in recently established and rapidly growing populations throughout the sea otter's North Pacific range, compared to energy intake rates ranging from 7 kcal/min to 11 kcal/min in long established, stable or slowly increasing populations where resource abundance is thought to be limiting further growth (Tinker et al . , Tinker , Coletti et al . ).…”

Section: Discussionmentioning

confidence: 99%

Influence of occupation history and habitat on Washington sea otter diet

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Tinker

et al. 2019

Marine Mammal Science

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Habitat characteristics are primary determinants of nearshore marine communities. However, biological drivers like predation can also be important for community composition. Sea otters (Enhydra lutris ssp.) are a salient example of a keystone species exerting top‐down control on ecosystem community structure. The translocation and subsequent population growth and range expansion of the northern sea otter (Enhydra lutris kenyoni) in Washington State over the last five decades has created a spatio‐temporal gradient in sea otter occupation time and density, and acts as a natural experiment to quantify how sea otter population status and habitat type influence sea otter diet. We collected focal observations of sea otters foraging at sites across the gradient in varying habitat types between 2010 and 2017. We quantified sea otter diet composition and diversity, and long‐term rates of energy gain across the gradient. We found that sea otter diet diversity was positively correlated with cumulative sea otter density, while rate of energy gain was negatively correlated with cumulative density. Additionally, we found that habitat type explained 1.77 times more variance in sea otter diet composition than sea otter cumulative density. Long‐term diet studies can provide a broader picture of sea otter population status in Washington State.

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Southern sea otter (Enhydra lutris nereis) population biology at Big Sur and Monterey, California --Investigating the consequences of resource abundance and anthropogenic stressors for sea otter recovery

Cited by 32 publications

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Gaps in kelp cover may threaten the recovery of California sea otters

Gaps in kelp cover may threaten the recovery of California sea otters

Location‐specific factors influence patterns and effects of subsistence sea otter harvest in Southeast Alaska

Influence of occupation history and habitat on Washington sea otter diet

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