Abstract
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 Columbia, Canada, varying in sea otter occupation time. Comparisons of mussel size spectra revealed that ancient mussel size distributions are consistently more similar to modern size distributions at locations with a prolonged absence of sea otters. This indicates that late Holocene sea otters were maintained well below carrying capacity near human settlements as a result of human intervention. These findings illuminate the conditions under which sea otters and humans persisted over millennia prior to the Pacific maritime fur trade and raise important questions about contemporary conservation objectives for an iconic marine mammal and the social-ecological system in which it is embedded.
Highlights
In 1998, Paul Dayton, Mia Tegner, and colleagues identified a challenge at the crux of endangered species management: population baselines cannot be defined without considering potential ecological ‘ghosts’ that served formerly consequential roles in marine ecosystems
Our results suggest that sea otters in the late Holocene were rare to absent near sites of human occupation, contrary to the general assumption that sea otters were at or Ancient Evidence of Low Sea Otter Prevalence near carrying capacity throughout their range prior to the Pacific maritime fur trade
Prior to the maritime fur trade which began in the late eighteenth century, sea otters ranged from Japan, north through the Aleutian Islands and down the Pacific coast of North America to Baja California (Barabash-Nikiforov 1947)
Summary
In 1998, Paul Dayton, Mia Tegner, and colleagues identified a challenge at the crux of endangered species management: population baselines cannot be defined without considering potential ecological ‘ghosts’ that served formerly consequential roles in marine ecosystems. In Canada, an emerging challenge exists between the recovery and protection status of sea otters, a well-recognized shellfish predator, and the constitutionally protected rights of Indigenous people to access those same shellfish The crux of this conservation and management conflict hinges on our perspective of historical baselines and the role humans once played, and continue to play, in coastal ecosystems (Salomon and others 2015; Pinkerton and others 2019; Burt and others 2020). Sea otters (Enhydra lutris) in Canada are protected under the federal Fisheries Act (R.S.C., 1985), and their recovery is defined as occurring when their ’long-term persistence in the wild is secured’ (Sea Otter Recovery Team 2007) Their conservation status is determined by their population trend over three generations (COSEWIC 2007). Both estimates are independent of human impacts and conservation targets are implicitly viewed as ’to allow full, pre-exploitation recovery’ (Davis and others 2019)
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