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Using seasonal variation in individual energetic requirements to simulate energy use in a population of harbor seals (Phoca vitulina)
 

Summary: Using seasonal variation in individual energetic requirements
to simulate energy use in a population of harbor seals (Phoca vitulina)
ABSTRACT
Harbor seals are a large-bodied and abundant marine predator in the ecosystem of the San Juan
Islands, USA, and therefore may impact the success of marine protected areas by preying on
recovering fish species. Understanding prey consumption first requires an understanding of
individual energetics and their potential seasonal variation to simulate population energetics. We
used time-depth recorder data to quantify activity budgets of harbor seals to build a population-
level bioenergetics model that considered breeding (15 June - 15 Sept) and non-breeding (16 Sept
- 14 June) periods. A total of 11 female and 8 male seals were tagged at rocky-reef sites (n = 8)
and in an estuarine bay (n = 11) in 2007 and 2008. Female activity budgets were relatively
consistent between sites and seasons, while males were more variable overall. Females increased
the amount of time spent diving by 23% during the non-breeding season and hauled-out at a
constant rate year-round (17% of time budget), while male dive effort and haul-out rates varied
greatly between individuals and physical habitats. Physiological variables, including body mass
and activity levels, influenced the prediction of population-level energy use to a greater extent
than other model variables (population size and fecundity rates), and accounted for > 80% of the
variance in model outputs. Population energy use was 10% greater during the breeding season,
indicating that seasonal variation may be important in predicting potential impacts of predators
on prey resources and marine reserve goals. Population energetic requirements can be combined

  

Source: Acevedo, Alejandro - Department of Biology, Western Washington University

 

Collections: Environmental Sciences and Ecology