CLASSIFYING PREY HARD PART STRUCTURES RECOVERED FROM FECAL REMAINS OF CAPTIVE STELLER SEA LIONS (EUMETOPIAS JUBATUS)

Feces were collected from six Steller sea lions ( Eumetopias jubatus ) that consumed known amounts of Atka mackerel ( Pleurogrammus monopterygius ), Pacific herring ( Clupea barengus ), pink salmon ( Oncorhynchus gorbuscha ), walleye pollock ( Theragra chalcogramma ), and squid ( Loligo opalacens ). The goal was to determine the numbers and types of taxon-specific hard parts that pass through the digestive tract and to develop correction factors for certain abundantly occurring structures. Over 20,000 fish and squid were consumed during 267 d of fecal collection. During this period, over 119,000 taxon-specific hard parts, representing 56 different structures, were recovered. Skeletal structures and non-skeletal structures accounted for 72% and 28% of all hard parts, respectively. The branchiocranium, axial skeleton, and dermocranium regions of the skeletal system accounted for the greatest number of hard parts recovered. Over 70% of all recovered hard parts were represented by one to six taxa specific structures for each prey type. The average number of hard parts (3.1–31.2) and structure types (2.0–17.7) recovered per individual prey varied across taxa and were used to derive correction factors (to reconstruct original prey numbers). A measure of the variability of hard part recovery among sea lions showed no difference for certain herring, pollock, and squid structures, however, there was a significant difference for salmon and Atka mackerel structures. Identifying all taxon- specific prey hard parts increases the likelihood of identifying and estimating the number of prey consumed.