The use and abuse of fish otoliths in studies of feeding habits of marine piscivores

Abstract

The form and structure of fish otoliths are species specific, allowing them to be used as an aid in identification of prey species consumed by piscivores. Otholith length-fish length relationships can have application in the estimation of the size of fish prey consumed by squid, but, because otoliths are relatively rapidly attacked by acidic solutions, these relationships can not be used routinely for the estimation of the size of fish taken by marine mammals, birds and predatory fishes. Evidence from recent physiological studies of gastrointestinal motility suggests that indigestible material (skeletal fragments and otoliths) would not accumulate in the stomachs of marine mammals and birds, and any otoliths found amongst stomach contents probably represent the remains of a single feeding bout. Thus, the identification and counting of otoliths could provide a quantitative estimate of consumption of numbers of fish within different species. Results of anal)(ses of faecal material may not give accurate assessment of the spectra of prey consumed and such results should not be relied upon in quantitative estimation of prey consumed by marine piscivores.