Historical Ecology of Late Holocene Sea Otters (Enhydra lutris) from Northern British Columbia: Isotopic and Zooarchaeological Perspectives (original) (raw)
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Journal of Archaeological Science, 2012
We examined the isotopic composition of sea otter (Enhydra lutris) bone collagen from ten late Holocene (ca. 5200 years BP – AD 1900) archaeological sites in northern British Columbia (BC), Canada. Because sea otters are now extinct from much of this region and have not fully re-colonized their former range (e.g. Haida Gwaii and most of northern BC) these data represent an important first step towards better understanding sea otter foraging ecology in BC. The isotopic data suggest a diet composed primarily of benthic invertebrates, with a very low reliance on epibenthic fish. There is very low isotopic and thus inter-individual dietary variability in Holocene BC sea otters during the late Holocene. Furthermore, zooarchaeological abundance data suggest that otters represented a widespread and significant focus of aboriginal hunting practices on the northern BC coast during the mid-to late-Holocene. The consistent reliance on a small number of low trophic level prey and limited dietary variability in Holocene BC sea otters, may reflect top-down impacts on otter populations by aboriginal peoples. As part of our assessment of sea otter diet, we review trophic discrimination factors (Δ13C and Δ15N) for bone collagen from published literature and find marked variability, with mean values of 20 +3.7±1.6 for Δ13C (n=21) and +3.6±1.3 for Δ15N (n=15). Keywords: Sea Otter; British Columbia; Stable Isotopes; Quantifying Isotopic Variability; Zooarchaeology; Historical Ecology; Ecology of Fear
We examined the isotopic composition (δ13C and δ15N) of sea otter (Enhydra lutris) bone collagen from late Holocene (ca. 5200 years BP – AD 1900) archaeological sites in northern British Columbia, Canada. These data suggest that sea otter diets were composed primarily of benthic invertebrates, with a very low reliance on epibenthic fish. Given the large number of potential prey for sea otters based on studies of extant populations, there is very little isotopic and thus dietary variability in BC sea otters during the late Holocene, suggesting a lack of individual dietary specialization. This lack of piscivory and dietary specialization, combined with the abundance of sea otters in faunal assemblages, is suggestive of top-down control on sea otter populations through consistent, but sustainable, hunting by aboriginal peoples. ** This presentation was the winner of the 2011 Barbara Lawrence Award for Best Student Paper at the Annual Meeting of the Society for Ethnobiology ** Later published as: Szpak, P., Orchard, T.J., McKechnie, I., Gröcke, D.R., 2012. Historical Ecology of Late Holocene Sea Otters (Enhydra lutris) from Northern British Columbia: Isotopic and Zooarchaeological Perspectives. J. Archaeol. Sci. doi: 10.1016/j.jas.2011.12.006.
Sea otters (Enhydra lutris) were once ubiquitous on the Pacific coast of North America until they were reduced to the brink of extinction following the maritime fur trade (ca. 1780s – 1830s). Based almost entirely on data from Alaska and California, the role of the sea otter as a ‘keystone species’ in nearshore communities has been discussed extensively. Because the sea otter has yet to be reestablished in much of its former range (particularly in British Columbia, Washington and Oregon) very little is known about the regional variability in sea otter foraging ecology and it is difficult to predict the potential effects of future range expansions on the structuring of nearshore ecosystems and fisheries. In this paper we present isotopic data (δ13C and δ15N of bone collagen) for sea otters from ten Late Holocene archaeological sites in British Columbia. The data demonstrate a high reliance on benthic invertebrates (sea urchins, clams, mussels) and a surprising lack of dietary variability given the wide range of potential sea otter prey items. Some animals from fur trade era deposits also display divergent δ13C values, suggesting that either (1) significant changes had occurred to nearshore ecosystems prior to the complete removal of sea otters, or (2) these animals were acquired through trade. We discuss both of these possibilities in light of isotopic data from other nearshore species (epibenthic fish) from the same archaeological contexts. Later published as: Szpak, P., Orchard, T.J., McKechnie, I., Gröcke, D.R., 2012. Historical Ecology of Late Holocene Sea Otters (Enhydra lutris) from Northern British Columbia: Isotopic and Zooarchaeological Perspectives. J. Archaeol. Sci. doi: 10.1016/j.jas.2011.12.006.
Ecosystems, 2021
The historic extirpation and subsequent recovery of sea otters (Enhydra lutris) have profoundly changed coastal social-ecological systems across the northeastern Pacific. Today, the conservation status of sea otters is informed by estimates of population carrying capacity or growth rates independent of human impacts. However, archaeological and ethnographic evidence suggests that for millennia, complex hunting and management protocols by Indigenous communities limited sea otter abundance near human settlements to reduce the negative impacts of this keystone predator on shared shellfish prey. To assess relative sea otter prevalence in the Holocene, we compared the size structure of ancient California mussels (Mytilus californianus) from six archaeological sites in two regions on the Pacific Northwest Coast, to modern California mussels at locations with and without sea otters. We also quantified modern mussel size distributions from eight locations on the Central Coast of British Col...