DIET OF GRAY WHALES (ESCHRICHTIUS ROBUSTUS) IN CLAYOQUOT SOUND, BRITISH COLUMBIA, CANADA

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Abstract

In Clayoquot Sound, British Columbia, gray whales (Eschrichtius robustus) forage for pelagic, hyperbenthic, and benthic invertebrates. Prey types were collected near feeding whales and at sites where no whales were observed to ascertain whales' diets and to describe prey populations and distributions. Characteristics of prey that are examined include species composition, density, biomass, and size. Whales foraged for mysids, Holmesimysis sculpta being the most abundant species collected. Whales foraged near concentrated patches of porcelain crab zoeal larvae, composed primarily of Pachycheles rudis, 21 –294 times the average density and biomass normally collected. Amphipod biomass, composed primarily of Ampelisca agassizi and A. careyi, was 160 ± 150 g/m2 where whales foraged. Larger amphipods, rather than higher density, resulted in higher amphipod biomass between years. Whales foraged where there was a high proportion (61%) of amphipods > 6 mm in length. Whales initially foraged for amphipods along the 20-m depth contour line; amphipod biomass was best developed and least variable at depths between 16 and 20 m.

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