Foraging behavior and prey of sea otters in a soft- and mixed-sediment benthos in Alaska

Abstract

a b s t r a c tSea otter (Enhydra lutris kenyoni) foraging behavior and prey preference were studied from June to August 2001August -2004 in Simpson Bay, Prince William Sound, Alaska. The study area has an average water depth of 30 m and a benthos primarily of soft-and mixed-sediment with no canopy-forming kelps. A total of 1816 foraging dives from 211 bouts were recorded. Overall, dives ranged in depth from <5 to 82 m; most dives were less than 15 m (40%) with smaller, secondary peaks at 25-30 m (10%) and 50-55 m (7%). Average dive depth and duration were 27 m ± 19.5 and 1.89 min ± 0.88, respectively. Dive durations were all significantly different: male > unknown > female. Dive depths reflected the bathymetry (percentage of the bay within a depth range) of Simpson Bay but favored shallow areas. 87% of foraging dives were successful, and 44% of the prey was positively identified: 75% clams, 9% Pacific blue mussels, 6% crabs, 2% Reddish scallops and a variety of other invertebrates. There was no evidence for prey specialization among the sexes. Although sea otters in Simpson Bay rely heavily on bivalves, their diet has remained unchanged for the past 18 years, and the minimum summer population has been constant for at least the past nine years. It appears that bivalves are the predominant and stable component of the diet, and their productivity is sufficient to sustain a stable population of sea otters with a minimum peak summer density of 4.3 adult otters km −2 and an average annual density of ca. 2.9 adult otters km −2 for the past nine years and probably longer.

Diet of northern sea otters (Enhydra lutris kenyoni) from Icy Strait, Alaska, based on stomach contents analysis

“…, Wolt et al . ). The results of the present study update a previous study of sea otter diet based on stomach content analysis (Kenyon ) and advance knowledge of sea otter diet in soft‐sediment habitats in Alaska.…”

Future Directions in Sea Otter Research and Management

“…Other populations, such as the one in California, experienced more modest growth see Question 1). Because of their elevated resting metabolic rate and food consumption (∼25% of body weight per day, primarily benthic invertebrates; Costa and Kooyman, 1984;Yeates et al, 2007;Wolt et al, 2012), sea otters are widely recognized as susceptible to density-dependent competition for food (Kenyon, 1969;Estes, 2015). As sea otters reoccupy an area, populations of epibenthic prey such as sea urchins, crabs and abalone generally decline first followed by infaunal species such as large bivalves, depending on habitat Kvitek et al, 1993).…”

Assessing Risks to Sea Otters and theExxon ValdezOil Spill: New Scenarios, Attributable Risk, and Recovery

“…The model's characteristics, sources of data, and results for the base model and the initial set of sensitivity analysis scenarios are presented in Harwell et al (2010a) . Briefly, our IBM simulates all plausible pathways for PAH exposures in the Sound ( Figure 2 ), where sea otters feed primarily on epibenthic invertebrates like mussels or on infauna excavated from sediments, primarily clams ( Calkins 1978 ; Doroff and Bodkin 1994 ; Johnson and Garshelis 1995 ; Dean et al 2002 ; Harwell et al 2012 ; Wolf et al 2012 ). The sea otter's diet in the ITZ of the oil-affected part of the Sound is ∼50% clams (infauna) and 40% mussels (epifauna), whereas the subtidal zone (STZ) diet is ∼75% clams ( Harwell et al 2010a ; Wolf et al 2012 ).…”

“…Briefly, our IBM simulates all plausible pathways for PAH exposures in the Sound ( Figure 2 ), where sea otters feed primarily on epibenthic invertebrates like mussels or on infauna excavated from sediments, primarily clams ( Calkins 1978 ; Doroff and Bodkin 1994 ; Johnson and Garshelis 1995 ; Dean et al 2002 ; Harwell et al 2012 ; Wolf et al 2012 ). The sea otter's diet in the ITZ of the oil-affected part of the Sound is ∼50% clams (infauna) and 40% mussels (epifauna), whereas the subtidal zone (STZ) diet is ∼75% clams ( Harwell et al 2010a ; Wolf et al 2012 ). To collect clams, a sea otter excavates a pit by digging several centimeters into the sediments until clams are encountered ( Shimek and Monk 1977 ; Calkins 1978 ; Hines and Loughlin 1980 ; Kvitek et al 1988 ).…”