EFFECTS OF MEAL SIZE ON OTOLITH RECOVERY FROM FECAL SAMPLES OF GRAY AND HARBOR SEAL PUPS

Recovered otoliths from pinniped feces provide valuable information on diet composition and prey size. We studied the effect of meal size on otolith recovery from the feces of one harbor and eight gray seal pups. Each of 11 experiments comprised a half-ration meal, a period of fecal collection, a 1.5-or double-ration meal again followed by a period of fecal collection. A significantly lower percentage of Atlantic herring otoliths were recovered from half-ration meals (25%± 12.5% in the harbor seal, 8.6%± 6.9% in eight gray seals) than from 1.5- or double-ration meals (62.5%± 3.1 % in the harbor seal, 32.8%± 23.5% in gray seals). Meal size also significantly affected the percentage of Atlantic cod otoliths recovered from gray seal feces (65.0%± 26.3% from half ration, 98.3%± 2.9% from 1.5 ration). For both size meals, recovered cod otoliths were more significantly eroded than herring otoliths. The development of correction factors to account for the effects of digestion will need to consider the distribution of meal sizes of free-ranging pinnipeds.