Influence of occupation history and habitat on Washington sea otter diet

Abstract

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.

Southeast Alaskan kelp forests: inferences of process from large-scale patterns of variation in space and time

“…Kelp forests, in turn, have a broad array of knock-on effects (sensu [13]) on other species and ecological processes [14]. Sea otters are also voracious predators of other shellfish, including abalone, mussels and clams [15][16][17]. The negative direct effect of sea otters on their macroinvertebrate prey can manifest as human costs because the sea otters' macroinvertebrate prey base is also the foundation for several commercial, subsistence and recreational shellfisheries.…”

Archaeological and Contemporary Evidence Indicates Low Sea Otter Prevalence on the Pacific Northwest Coast During the Late Holocene

“…The degree to which sea otter occupation time can predict the size structure of its prey varies as a function of predator population density, rate of range expansion, predator–prey selectivity, and prey capture rates, each of which are affected by factors such as prey quantity, quality, and productivity, as well as habitat diversity and shoreline complexity (Hoyt 2015 ; Hessing-Lewis and others 2018 ; Hale and others 2019 ; Smith and others 2021 ). Comparatively, the South Coast region contains five times the sea otter population on a more linear coastline relative to the Central Coast region which encompasses a greater multitude of small islands, deep fjords, and channels.…”

“…Though many factors affect the size and growth rate of intertidal and subtidal macroinvertebrates, sea otters have been documented to exert strong top-down control resulting in reduced average sizes of their prey across a variety of habitats and environmental conditions (Estes and Palmisano 1974 ; Kvitek and others 1992 ; Fanshawe and others 2003 ; Salomon and others 2007 ; Singh and others 2013 ; Lee and others 2016 ; Burt and others 2018 ; Hale and others 2019 ). In some cases, environmental variation affecting macroinvertebrate growth rates have been found to have minimal effect in comparison with sea otter predation.…”

Behavioral observations and stable isotopes reveal high individual variation and little seasonal variation in sea otter diets in Southeast Alaska

“…The importance of sea otters Enhydra lutris in shaping nearshore marine ecosystems is well documented along the northeast Pacific coast (Estes & Palmisano 1974, Hughes et al 2013, Rechsteiner et al 2019, Hale et al 2019. Sea otters are keystone predators with voracious appetites capable of causing major ecological shifts in nearshore marine ecosystems (Estes et al 2016).…”