Abstract: inter-annual variation in harbour seal diet (fwd)

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    Subject: Abstract: inter-annual variation in harbour seal diet (fwd)

    Interannual variation in the summer diets of harbour seals Phoca vitulina at
    Mousa, Shetland (UK)

    Brown, E.G., Pierce, G.J., Hislop, J.R.G. & Santos, M.B. (2001) Journal of
    the Marine Biological Association of the UK, 81, 325-337.

    ABSTRACT

    The main prey species in the summer (July-September) diets of harbour seals
    (Phoca vitulina) on the Island of Mousa (Shetland, UK), 1994-1997, were
    whiting (Merlangius merlangus), herring (Clupea harengus), sandeel
    (Ammodytidae) and garfish (Belone belone). Norway pout (Trisopterus
    esmarkii) was numerically important but comprised no more than 11% of prey
    weight in any one year. There were marked between-year fluctuations in the
    relative importance of these prey, with whiting comprising 16-34% (by
    weight) of the diet, herring 12-28%, sandeels 7-18% and garfish 7-22%.
    Additional data on spring (April-June) diet were available for 1995-1997:
    sandeels were the most important prey (% weight) in all three years (51-60%
    of the diet), while herring (8-48%) and gadids (2-22%) varied in importance.
    The average size of fish eaten was larger than that reported in comparable
    studies from other areas. Harbour seals appear to have selected larger
    sandeels, whiting, and Norway pout than the average size available in the
    area, as indicated by survey trawls, although between-year changes in the
    size of Norway pout in the diet did to some extent reflect availability.
    Interannual variation in the importance of Norway Pout in the diet appeared
    to track trends in abundance, although the short time series precluded
    detection of a statistically significant correlation. Thus, some of our
    results are consistent with harbour seals feeding opportunistically while
    others point to selectivity, particularly for prey size. Estimated
    consumption of fish by the 500 harbour seals on Mousa during summer ranged
    from 152-195 tonnes.

    Reprint requests to:

    Edward G. Brown
    9 Twageos Rd
    Lerwick
    Shetland
    ZE1 0BB
    Scotland, U.K.

    Email: e.brown@ssmg.shetland.co.uk

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