Subject: abstract - harp seal foraging (fwd)

Mike Williamson (pita@www1.wheelock.edu)
Fri, 17 Apr 1998 10:21:01 -0400 (EDT) 

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---------- Forwarded message ----------
Date: Thu, 16 Apr 1998 10:38:28 -0400
From: Dagmar Fertl <Dagmar_Fertl@mms.gov>
Reply-To: Marine Mammals Research and Conservation Discussion
     <MARMAM@UVVM.UVIC.CA>
To: MARMAM@UVVM.UVIC.CA
Subject: abstract - harp seal foraging

     The following article might be of interest; full text may be found at:

     http://www.int-res.com/journals/meps


     Lawson JW, Anderson JT, Dalley EL, Stenson GB.  1998.  Selective
     foraging by harp seals _Phoca groenlandica_ in nearshore and offshore
     waters of Newfoundland, 1993 and 1994.  _Marine Ecology Progress
     Series_ 163:1-10

     ABSTRACT: The harp seal Phoca groenlandica, which is numerous and
     widespread in the Northwest Atlantic, may have significant influences
     on the structure of this ecosystem. To quantify this influence, we
     must understand the functional relationship between harp seals and
     their prey. If seals are discriminating in their choice of prey, then
     their consumption of a particular species will not necessarily vary in
     relation to its availability or catchability. By applying Chesson's
     index of selectivity to stomach contents and research trawl data
     collected in several near- and offshore locations, we found that harp
     seals preferentially selected capelin Mallotus villosus relative to
     other prey species, irrespective of their local abundance, when given
     the choice. Arctic cod Boreogadus saida were also preferred in
     nearshore areas, but not in the offshore. In general, these predators
     were neutrally selective towards Atlantic cod Gadus morhua, American
     plaice Hippoglossoides platessoides and Greenland halibut
     Reinhardtius hippoglossoides. These patterns rationalize the dietary
     patterns reported for harp seals generally. They also explain
     the harp seals' switch from a reliance on capelin to Arctic cod seen
     in the mid 1980s, when evidence suggests these cod became
     more abundant than capelin in nearshore waters (where their
     respective energy densities are similar).