More than any other nonhuman species, it was the sea otter that defined the world's largest oceanscape prior to the California gold rush. In addition to the more conventional aspects of the sea otter ...trade, including Russian expansion in Alaska, British and American trading in the Pacific Northwest, and Spanish colonial ventures along the California coast, the global importance of the species can be seen in its impact on the East Asian maritime fur trade. This trade linked Imperial China, Japan, and indigenous Ainu peoples of the Kurile Islands as early as the fifteenth century.InSea Otters: A HistoryRichard Ravalli synthesizes anew the sea otter's complex history of interaction with humans by drawing on new histories of the species that consider international and global factors beyond the fur trade, including sea mammal conservation, Cold War nuclear testing, and environmental tourism. Examining sea otters in a Pacific World context, Ravalli weaves together the story of imperial ambition, greed, and an iconic sea mammal that left a determinative imprint on the modern world.
Abstract
Despite its recent invasion into the marine realm, the sea otter (Enhydra lutris) has evolved a suite of adaptations for life in cold coastal waters, including limb modifications and dense ...insulating fur. This uniquely dense coat led to the near-extinction of sea otters during the 18th–20th century fur trade and an extreme population bottleneck. We used the de novo genome of the southern sea otter (E. l. nereis) to reconstruct its evolutionary history, identify genes influencing aquatic adaptation, and detect signals of population bottlenecks. We compared the genome of the southern sea otter with the tropical freshwater-living giant otter (Pteronura brasiliensis) to assess common and divergent genomic trends between otter species, and with the closely related northern sea otter (E. l. kenyoni) to uncover population-level trends. We found signals of positive selection in genes related to aquatic adaptations, particularly limb development and polygenic selection on genes related to hair follicle development. We found extensive pseudogenization of olfactory receptor genes in both the sea otter and giant otter lineages, consistent with patterns of sensory gene loss in other aquatic mammals. At the population level, the southern sea otter and the northern sea otter showed extremely low genomic diversity, signals of recent inbreeding, and demographic histories marked by population declines. These declines may predate the fur trade and appear to have resulted in an increase in putatively deleterious variants that could impact the future recovery of the sea otter.
Differences in diet composition among conspecifics (dietary specialization) have been documented across a broad range of taxonomic groups and habitats, and such variation at the individual level is ...increasingly recognized as an important component of diversity in trophic interactions. Accurate identification of individual dietary specialization, however, requires longitudinal dietary records that are labor-intensive and cost-prohibitive to obtain for many species. Here we explore the use of stable isotopes (δ¹³C and δ¹⁵N) as a promising technique for detecting and quantifying patterns of individual dietary specialization. Southern sea otters (Enhydra lutris nereis) offer a unique opportunity for testing this approach because (1) they consume a wide variety of prey that span multiple trophic levels, habitats, and ecologically defined functional groups; and (2) individual diet specialization can be validated with existing observational data. We analyzed the isotopic composition of sea otter vibrissae (n = 31) in order to characterize inter- and intra-individual variation in sea otter diets at Monterey Bay, California, USA. At the population level, sea otters showed substantial variation in both δ¹³C and δ¹⁵N values, occupying nearly all of the "isotopic space" created by the diversity of isotopic signatures of potential prey taxa. Most of the variation in sea otter vibrissae was accounted for by differences between individuals, with much less contributed by within-individual variation. A majority of sea otters (∼80%) showed relatively little temporal variability in isotopic composition, suggesting that the proportional composition of most individuals' diets is relatively constant over time; a few individuals (∼20%) exhibited a high degree of intra-vibrissa isotopic variability, suggesting seasonal shifts in diet composition. These results and our interpretation of them were supported by long-term observational data on the diets of radio-tagged sea otters from the same population (n = 23). Our results demonstrate that stable isotopes can provide an efficient tool for measuring individual- and population-level dietary breadth and may be useful for studying populations where longitudinal data on individuals would otherwise be impossible to acquire. This will be critical for examining the causes and consequences of dietary variation within and among consumer populations, thereby improving our understanding of these important ecological and evolutionary processes at the community level.
Why some Toxoplasma gondii-infected southern sea otters (Enhydra lutris nereis) develop fatal toxoplasmosis while others have incidental or mild chronic infections has long puzzled the scientific ...community. We assessed robust datasets on T. gondii molecular characterization in relation to detailed necropsy and histopathology results to evaluate whether parasite genotype influences pathological outcomes in sea otters that stranded along the central California coast. Genotypes isolated from sea otters were also compared with T. gondii strains circulating in felids from nearby coastal regions to assess land-to-sea parasite transmission. The predominant T. gondii genotypes isolated from 135 necropsied sea otters were atypical Type X and Type X variants (79%), with the remainder (21%) belonging to Type II or Type II/X recombinants. All sea otters that died due to T. gondii as a primary cause of death were infected with Type X or X-variant T. gondii strains. The same atypical T. gondii strains were detected in sea otters with fatal toxoplasmosis and terrestrial felids from watersheds bordering the sea otter range. Our results confirm a land-sea connection for virulent T. gondii genotypes and highlight how faecal contamination can deliver lethal pathogens to coastal waters, leading to detrimental impacts on marine wildlife.
An innovative trawling strategy for transitioning from conventional bottom trawling to semi-pelagic trawling (elevating the otter board but allowing the trawl net to contact the seabed) was developed ...to mitigate the effects of seabed impact, and its dynamic performance was evaluated. Experiments were carried out using a 1/18 scale physical model of the otter trawl at a speed of 0.6 m/s, and the warp length was tuned in the range of 4–8 m under constant-speed control of the trawl winch for validating the numerical simulations. Numerical simulations were then conducted to investigate the effects of towing speed and winch speed on the dynamic loads of the otter trawl system and movement of the otter board, eventually develop a fuzzy or proportion-integration-differentiation (PID) controller for the trawl system. Numerical results showed the sharp increase of the warp tension and the overshoot of the otter board at the constant-speed control occurred, and the magnitudes of both raised as the towing speed and winch speed increased. The otter board spread was significantly reduced during the transition to semi-pelagic trawling at a low towing speed. The use of fuzzy and PID control successfully eliminated the overshoot and diminished the high warp tension.
•Effects of towing and winch speeds on the dynamic performances of otter trawl were investigated as the trawl tows semi-pelagically.•Trawl winch reeling in warp faster, both the maximum warp tension and the otter board overshoot larger.•A reduction of otter-board spread from the bottom towards semi-pelagic trawl occurs when the towing speed is low.•Automated trawl winch could eliminate the otter board overshoot and diminish the high warp tension for the semi-pelagic trawl.
In this study, we investigate whether replacing conventional seabed-contacting otter boards with semi-pelagic self-adjusting otter (SAO) boards, which have the ability to maintain a given height ...above the seabed, affects the catch efficiency of a demersal fish trawl. Experimental fishing trials, using the alternate haul method, were conducted in the Kattegat and Skagerrak with three otter board configurations using conventional seabed-contacting otter boards; the SAO set to maintain a target height over the seabed of 1 m; and the SAO set to maintain a target height of 5 m. Replacing conventional otter boards with SAO resulted in a loss of catch efficiency for haddock ( Melanogrammus aeglefinus), whiting ( Merlangius merlangus), and plaice ( Hippoglossoides platessoides), while no significant difference was found for cod ( Gadus morhua), common dab ( Limanda limanda), and lemon sole ( Microstomus kitt). When comparing the SAO-1 m and SAO-5 m, it was observed that SAO-5 m resulted in a loss of catch efficiency for haddock and plaice, a minimal reduction for cod, and no significant difference for whiting, common dab, and lemon sole.
Some taxa of mammals live in water, all of which evolved from land-dwelling ancestors. In the family Mustelidae (Mammalia: Carnivora), most species live on land, while otters, comprising the ...subfamily Lutrinae, inhabit aquatic environments, which include the almost exclusively aquatic sea otters (Enhydra lutris). Thus, the transition from a terrestrial to an aquatic lifestyle has occurred within this family. Despite potentially different selection pressures on body size in aquatic and terrestrial habitats, no divergence in the evolutionary pattern of body size between otters and other mustelids has previously been shown using models of trait evolution on a phylogeny. We applied models that explicitly incorporated lineage-specific directional selection to the evolution of body mass in living mustelids. Using a simulation-based likelihood and approximate Bayesian computation approach, we demonstrated lineage-specific directional selection for larger body mass in otters, which is distinct from other mustelids. There was no evidence of a difference between sea otters and other otters in the strength of directional selection for larger body mass. Additionally, our analyses supported no difference in the rate at which body mass evolves in both directions between otters and other mustelids. These findings suggest that the evolution of body mass in otters is associated with selective advantages of larger size rather than the relaxation of constraints on body size in aquatic habitats, like other aquatic mammals such as sirenians, cetaceans, and pinnipeds.
Lutra lutra (Linnaeus, 1758), commonly known as the Eurasian otter, is the most widely distributed of the lutrinids (otters). L. lutra is primarily a piscivorous predator but also preys on ...amphibians, crustaceans, small mammals, birds, and reptiles. Extant populations of this semiaquatic mustelid occur in a wide variety of aquatic freshwater and marine habitats throughout Asia, all of Europe, and parts of northern Africa. Despite the large distribution, habitat loss has led to dwindling L. lutra populations, particularly in Asia, and the species is currently listed as “Near Threatened” by the International Union for Conservation and Nature and Natural Resources.
The threatened Gangetic dolphin (Platanista gangetica) and smooth-coated otter (Lutrogale perspicillata) occuring in the Ganga River Basin (GRB), are experiencing a decline in their population and ...distribution range owing to multiple anthropogenic pressures, including pollution by Potentially Toxic Elements (PTEs). Apex predators primarily encounter contaminants through dietary exposure. Yet, notable gaps persist in our understanding of the risks associated with the ingestion of PTE-contaminated prey for Gangetic dolphins and smooth-coated otters. In this study, we examined the occurrence and spatial variation of PTEs in the prey (fish) of both these riverine mammals across three major rivers of the Basin, while also evaluating the associated risk of ingesting contaminated prey. Our assessment revealed no statistical variation in bioaccumulation profiles of PTEs across the three rivers, attributable to comparable land use patterns and PTE consumption within the catchment. Zn and Cu were the most dominant PTEs in the prey species. The major potential sources of pollution identified in the catchment include agricultural settlements, vehicular emissions, and the presence of metal-based additives in plastics. Zn, As and Hg accumulation vary with the trophic level whereas some PTEs show concentration (Hg) and dilution (As, Cr, Pb and Zn) with fish growth. The Risk Quotient (RQ), based on the dietary intake of contaminated prey calculated using Toxicity Reference Value was consistently below 1 indicating no significant risk to these riverine mammals. Conversely, with the exception of Co and Ni, the Reference Dose-based RQs for all other PTEs indicated a substantial risk for Gangetic dolphins and smooth-coated otters through dietary exposure. This study serves as a pivotal first step in assessing the risk of PTEs for two threatened riverine mammals in a densely populated river basin, highlighting the importance of their prioritization in regular monitoring to reinforce the ongoing conservation efforts.
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•Zn and Cu were the most dominant PTEs in prey fish at all sampling sites.•No spatial variation observed in bioaccumulation of PTEs among three rivers.•As And Co levels in benthopelagic fish were higher than in pelagic and demersal fish.•Hg biomagnifies along the food chain, whereas As and Zn show trophic dilution.•As, Hg, Cr, Zn, Cu, and Cd, poses high risk to these threatened species.
Toxoplasma gondii is a ubiquitous parasitic protozoan that poses a health threat to wildlife and human health worldwide. Oocysts shed into the environment in felid host feces may persist for several ...years. Runoff from rainfall and snowmelt may carry the oocysts into waterways. Semiaquatic mammals such as the Northern American river otter (Lontra canadensis) are particularly at risk of exposure, as they may encounter infective stages in both terrestrial and aquatic environments. Despite this risk, only a small number of studies have examined the prevalence of T. gondii in US river otter populations. Tongue tissue was sampled from 124 otters from the Upper Peninsula of Michigan submitted by trappers to the Michigan Department of Natural Resources in the 2018-19 harvest season. Following DNA extraction, a portion of the B1 T. gondii gene was amplified with PCR. A subset of positive samples was genotyped for comparison with known T. gondii sequences. Of the 124 tongue samples, 35 (28%) were positive for T. gondii. Prevalence did not differ significantly between sexes or age classes across the entire study area. Most (53.8%) of the genotyped samples were type 4 (type 12), a genotype commonly found in North American wildlife. Genotypes 127 and 197 were also found. Three clusters of T. gondii prevalence were identified through SaTScan analysis, although they were not significant. When modeling prevalence of T. gondii with covariates at individual otter locations, the top three models included the presence of Sarcocystis, area of exotic plants, area of agriculture, and sex of the otter. Our results suggest that T. gondii is widespread in otter populations in the Upper Peninsula of Michigan.
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