Recent advances in diet analysis of marine mammals

Abstract Analysis of marine mammal diets has traditionally been based on identification of fish otoliths recovered from stomachs and faeces. However, not all prey species have otoliths which appear in stomachs or faeces. One promising new approach is the identification of fish muscle protein residues using specific antisera. This methodology has been validated for salmonid and sandeel proteins and has been successfully applied to field studies of common seal and grey seal diets. Further development is required for routine use on a wider scale. Fish prey have also been identified from other hard remains, although there are few guides or keys. Discriminant analysis of bone morphometrics may assist identification of prey species. The sizes of fish eaten are normally estimated from measurements of otoliths or bones, but a major difficulty is the differential degradation of these hard parts. Degradation of otoliths and bones in vitro has helped to quantify reduction in size due to digestion. Analysis of marine mammal diets has traditionally relied on identification of hard remains of prey in stomach contents and faeces. In the case of piscivorous species, diets are primarily assessed by identifying and counting fish otoliths. Prey importance may be further quantified by calculating fish weight from measurements of otoliths. Similar methods may be applied to species feeding on cephalopods, the beaks of which are resistant to digestion. For species feeding primarily on other invertebrates, prey may be identified from remains of exoskeletons or shells.