California sea otter (Enhydra lutris nereis) census results, Spring 2017

Tinker, M. Tim; Hatfield, Brian B.

doi:10.3133/ds1067

Cited by 17 publications

(41 citation statements)

References 3 publications

(2 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Demographic estimates for effective population size ( N e = 1,230) across the entire population were more than double the genetic estimates ( N e LD = 320, N e SF = 485); however, demographic and genetic estimates were consistent for otters in Monterey County (Table ). In comparison, the census population size at the end of our sampling period (2012) was 2,792 total sea otters, or 2,469 excluding dependent pups (Tinker & Hatfield, ).…”

Section: Resultsmentioning

confidence: 99%

“…Another factor that could increase genetic diversity would be an increase in the rate of population growth (Ortego, Calabuig, Cordero, & Aparicio, ). However, given the multiple threats impacting the southern sea otter population (including disease and shark bites), and because range expansion has stalled over the past two decades due to increased mortality at the northern and southern range peripheries (Lafferty & Tinker, ; Tinker & Hatfield, ; Tinker et al., ), it seems unlikely that demographic factors will enhance genetic diversity in the immediate future. Our findings also reveal that an increase in population size did not result in a corresponding increase in genetic diversity, suggesting that population size is not always a suitable substitution for direct measurements of genetic diversity, particularly for closed populations that have experienced severe population bottlenecks (Frankham, ).…”

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…Questions about population status are especially timely for southern sea otters because the population index has exceeded the 3,090 threshold for the last 2 censuses (Tinker & Hatfield, ; Tinker & Hatfield, ), and delisting consideration will be triggered if the index exceeds the threshold for a third year (US Fish and Wildlife Service, ). The population has increased in both abundance and distribution over the past several decades, with the current range extending along the mainland from Gaviota State Park in the south to Pigeon Point in the north, as well as San Nicolas Island in the southern California Bight (Tinker & Hatfield, ). Nevertheless, there are still contemporary threats to the population including the potential for an oil spill, increased mortality from lethal shark bites (Tinker, Hatfield, Harris, & Ames, ), as well as deaths from pathogens and toxicants associated with freshwater runoff (Jessup et al., ; Miller et al., ; Tinker et al., ).…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Measures of effective population size in sea otters reveal special considerations for wide‐ranging species

Gagne

Tinker

Gustafson

et al. 2018

Evolutionary Applications

View full text Add to dashboard Cite

Conservation genetic techniques and considerations of the evolutionary potential of a species are increasingly being applied to species conservation. For example, effective population size (N e) estimates are useful for determining the conservation status of species, yet accurate estimates of current N e remain difficult to obtain. The effective population size can contribute to setting federal delisting criteria, as was done for the southern sea otter (Enhydra lutris nereis). After being hunted to near extinction during the North Pacific fur trade, the southern sea otter has recovered over part of its former range, but remains at relatively low numbers, making it desirable to obtain accurate and consistent estimates of N e. Although theoretical papers have compared the validity of several methods, comparisons of estimators using empirical data in applied conservation settings are limited. We combined thirteen years of demographic and genetic data from 1,006 sea otters to assess multiple N e estimators, as well as temporal trends in genetic diversity and population genetic structure. Genetic diversity was low and did not increase over time. There was no evidence for distinct genetic units, but some evidence for genetic isolation by distance. In particular, estimates of N e based on demographic data were much larger than genetic estimates when computed for the entire range of the population, but were similar at smaller spatial scales. The discrepancy between estimates at large spatial scales could be driven by cryptic population structure and/or individual differences in reproductive success. We recommend the development of new delisting criteria for the southern sea otter. We advise the use of multiple estimates of N e for other wide‐ranging species, species with overlapping generations, or with sex‐biased dispersal, as well as the development of improved metrics of genetic assessments of populations.

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Measures of effective population size in sea otters reveal special considerations for wide‐ranging species

Gagne

Tinker

Gustafson

et al. 2018

Evolutionary Applications

View full text Add to dashboard Cite

show abstract

“…2B; Supplementary material Appendix 1 Table A5) during a period of local population decline from 2008-2016 (Tinker and Hatfield 2017). Instead, strandings due to neurological disease and shark bite have predominated in these regions ( Fig.…”

Section: Discussionmentioning

confidence: 99%

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

et al. 2018

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Rapid enhancement of multiple ecosystem services following the restoration of a coastal foundation species

Beheshti

Williams

Boyer

et al. 2021

Ecological Applications

View full text Add to dashboard Cite

The global decline of marine foundation species (kelp forests, mangroves, salt marshes, and seagrasses) has contributed to the degradation of the coastal zone and threatens the loss of critical ecosystem services and functions. Restoration of marine foundation species has had variable success, especially for seagrasses, where a majority of restoration efforts have failed. While most seagrass restorations track structural attributes over time, rarely do restorations assess the suite of ecological functions that may be affected by restoration. Here we report on the results of two small‐scale experimental seagrass restoration efforts in a central California estuary where we transplanted 117 0.25‐m2 plots (2,340 shoots) of the seagrass species Zostera marina. We quantified restoration success relative to persistent reference beds, and in comparison to unrestored, unvegetated areas. Within three years, our restored plots expanded ~8,500%, from a total initial area of 29 to 2,513 m2. The restored beds rapidly began to resemble the reference beds in (1) seagrass structural attributes (canopy height, shoot density, biomass), (2) ecological functions (macrofaunal species richness and abundance, epifaunal species richness, nursery function), and (3) biogeochemical functions (modulation of water quality). We also developed a multifunctionality index to assess cumulative functional performance, which revealed restored plots are intermediate between reference and unvegetated habitats, illustrating how rapidly multiple functions recovered over a short time period. Our comprehensive study is one of few published studies to quantify how seagrass restoration can enhance both biological and biogeochemical functions. Our study serves as a model for quantifying ecosystem services associated with the restoration of a foundation species and demonstrates the potential for rapid functional recovery that can be achieved through targeted restoration of fast‐growing foundation species under suitable conditions.

show abstract

California sea otter (Enhydra lutris nereis) census results, Spring 2017

Cited by 17 publications

References 3 publications

Measures of effective population size in sea otters reveal special considerations for wide‐ranging species

Measures of effective population size in sea otters reveal special considerations for wide‐ranging species

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

Rapid enhancement of multiple ecosystem services following the restoration of a coastal foundation species

Contact Info

Product

Resources

About