[MARMAM] New Publication: Fur seal consumption of commercially important prey

Elizabeth A McHuron emchuron at uw.edu
Thu Dec 3 08:46:24 PST 2020

Dear colleagues,

My collaborators and I are excited to announce the publication of our new
paper "Practical application of a bioenergetic model to inform management
of a declining fur seal population and their commercially important prey"
in Frontiers in Marine Science. The abstract is below and the full article
is available open-access here
Please feel free to reach out to me with any questions.

Happy Holidays!

Liz McHuron

Food availability is a key concern for the conservation of marine top
predators, particularly during a time when they face a rapidly changing
environment and continued pressure from commercial fishing activities.
Northern fur seals (*Callorhinus ursinus*) breeding on the Pribilof Islands
in the eastern Bering Sea have experienced an unexplained population
decline since the late-1990s. Dietary overlap with a large U.S. fishery for
walleye pollock (*Gadus chalcogrammus*) in combination with changes in
maternal foraging behavior and pup growth has led to the hypothesis that
food limitation may be contributing to the population decline. We developed
age- and sex-specific bioenergetic models to estimate fur seal energy
intake from May–December in six target years, which were combined with diet
data to quantify prey consumption. There was considerable sex- and
age-specific variation in energy intake because of differences in body
size, energetic costs, and behavior; net energy intake was lowest for
juveniles (18.9 MJ sea-day–1, 1,409.4 MJ season–1) and highest for adult
males (66.0 MJ sea-day–1, 7,651.7 MJ season–1). Population-level prey
consumption ranged from 255,232 t (222,159 – 350,755 t, 95% CI) in 2006 to
500,039 t (453,720 – 555,205 t) in 1996, with pollock comprising between
41.4 and 76.5% of this biomass. Interannual variation in size-specific
pollock consumption appeared largely driven by the availability of juvenile
fish, with up to 81.6% of pollock biomass coming from mature pollock in
years of poor age-1 recruitment. Relationships among metabolic rates, trip
durations, pup growth rates, and energy intake of lactating females suggest
the most feasible mechanism to increase pup growth rates is by increasing
foraging efficiency through reductions in maternal foraging effort, which
is unlikely to occur without increases in localized prey density. By
quantifying year-specific fur seal consumption of pollock, our study
provides a pathway to incorporate fur seals into multispecies pollock stock
assessment models, which is critical for fur seal and fishery management
given they were a significant source of mortality for both juvenile and
mature pollock.

Elizabeth McHuron, PhD
Research Scientist, UW CICOES
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