Feeding method affects otolith digestion in captive grey seals: implications for diet composition estimation

Kate Grellier, Philip Steven Hammond

Research output: Contribution to journalArticlepeer-review

12 Citations (Scopus)

Abstract

Analysis of prey structures from scats has become widely used for assessing the diet of free-ranging seals. Captive feeding experiments have played an important role in the development of scat analysis but methodology has varied. We investigated whether using an experimental otolith-carrier species or in situ otolith experimental prey to feed haddock, plaice, and sand eel otoliths to two captive gray seals affected the amount of otolith digestion, and therefore our ability to estimate fish size and diet composition. Otolith recovery rates varied among the three prey species, but were not affected by feeding method. Otoliths were more digested in carrier experiments; resulting digestion coefficients were greater than those from in situ experiments. As a result, while the lengths of whole fish fed experimentally could be accurately predicted by applying in situ digestion coefficients, the lengths of these fish could not be accurately predicted using carrier digestion coefficients. Consequently, the estimated proportion by weight of each species in the diet can change markedly when carrier, as opposed to in situ, digestion coefficients are used. The implications for diet composition estimation are significant.

Original languageEnglish
Pages (from-to)296-306
Number of pages11
JournalMarine Mammal Science
Volume21
Publication statusPublished - Apr 2005

Keywords

  • gray seal
  • Halichoerus grypus
  • diet composition
  • otolith digestion
  • captive feeding experiment
  • methodology
  • digestion coefficient
  • correction factor
  • recovery rate
  • HARBOR SEAL
  • FECAL SAMPLES
  • HARD PARTS
  • GREY SEALS
  • PREY
  • ISLAND
  • BEAKS
  • FECES
  • SIZE

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