Otolith size and location in digestive tracts of northern fur seals (Callorhinus ursinus): Implications for dietary interpretations |
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Authors: | E H Sinclair A E York G A Antonelis |
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Institution: | 1. National Marine Mammal Laboratory,7600 Sand Point Way NE,Seattle, Washington 98115, U.S.A.E‐mail: beth.sinclair@noaa.gov;2. 6018 Sycamore Avenue NWSeattle, Washington 98107, U.S.A.;3. Southwest Fisheries Science Center,2570 Dole Street,Honolulu, Hawaii 96822, U.S.A. |
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Abstract: | Walleye pollock (Theragra chalcogramma) otoliths (n= 2,706) recovered from stomachs, small intestines, and colons of 43 northern fur seals (Callorhinus ursinus) were evaluated for size and wear by location in the digestive tract. Pollock fork length was regressed on otolith length after correction for erosion, and age was estimated from the calculated body size. Age‐1+ pollock otoliths (≥6.3‐mm length) were concentrated in stomachs while age‐0 otoliths (≤6.2‐mm length) were concentrated in colons. Less than 10% of otoliths were found in the small intestines. Pollock age decreased with progression along seal gastrointestinal tracts. Otolith quality increased along gastrointestinal tracts in numbers ≥20, which was typical of age‐0 otoliths recovered from colons. Otolith distribution by age and quality along gastrointestinal tracts suggests that small (≤12 cm) schooling prey are consumed in large volume and passed as a bolus rapidly through the digestive tract before significant erosion of bony remains occurs; while larger prey are eaten in smaller volume and subjected to otolith erosion due to longer retention in the stomach. Our results illustrate the importance of multiple sampling strategies to comprehensively represent prey size in pinniped diet. |
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Keywords: | diet stomach scat Callorhinus ursinus northern fur seal pinniped pollock otolith prey size |
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