Subject: Abstract: harbour seal diet (fwd)

Mike Williamson (pita@www1.wheelock.edu)
Sun, 6 Sep 1998 09:21:20 -0400 (EDT)

Subject: Abstract of recent article on harbour seal diet

Brown, E.G. & Pierce, G.J. (1998) Monthly variation in the diet of harbour
seals in inshore waters along the southeast Shetland (UK) coastline. Marine
Ecology Progress Series, 167:275-289.
ABSTRACT: We studied the diets of harbour seals Phoca vitulina along the
southeast Shetland (UK) coastline by analysing prey remains found in faeces
(N = 733) at haul-out sites. A total of 44325 fish otoliths were recovered.
Sandeel (Ammodytidae) otoliths were the most numerous (38704), followed by
Gadidae (4707). Otoliths were measured and experimentally derived digestion
coefficients were applied (correcting for digestion in the seal's gut) to
estimate the size of ingested prey fishes. Gadids accounted for an
estimated 53.4% of the annual diet by weight, sandeels 28.5% and pelagic
fishes 13.8%. The dominant gadid fishes were whiting Merlangius merlangus
(25.3%) and saithe Pollachius virens (11.1%). The range of species observed
in the diet was similar to that recorded in other areas of the UK. One
exception to this was garfish Belone belone accounting for 34.1% of the
diet in September (1996), which is a species not previously reported for
harbour seal diets in UK waters. There were strong seasonal patterns in the
contribution of sandeels and gadids, with sandeels being important in
spring and early summer, and gadids in winter. Pelagic species (mainly
herring Clupea harengus, garfish and mackerel Scomber scombrus) were
important in late summer and autumn. Observed seasonal patterns are similar
to those previously recorded for harbour seal diets in the Moray Firth area
of Scotland and appear to coincide with changes in prey availability. A
comparison of the utility of using only otoliths to estimate seal diet with
all identifiable structures showed that using otoliths alone underestimated
the contribution of pelagic fish and overestimated the importance of gadids
and sandeels.
KEY WORDS: Harbour seal . Phoca vitulina . Otoliths . Shetland . Diet .
Seasonal variation

Requests for reprints should be sent to:

Edward G. Brown
9 Twageos Road
Lerwick
Shetland ZE1 0BB
Scotland UK
                or Email: e.brown@zetnet.co.uk