Subject: Abstract - humpback whales (fwd)

Michael Williamson (pita@whale.simmons.edu)
Thu, 19 Sep 1996 09:34:27 -0400 (EDT)

---------- Forwarded message ----------
Date: Tue, 17 Sep 1996 07:44:00 EST
From: Phil Clapham <CLAPHAM.PHIL@SIMNH.SI.EDU>
To: Multiple recipients of list MARMAM <MARMAM@UVVM.BITNET>
Subject: Abstract - humpback whales

Clapham, P.J. & Brownell, R.L. Jr.  1996.  The potential for interspecific
   competition in baleen whales.  Rep. int. Whal. Commn. 46: 361-367.

  Purported changes in the abundance and reproduction of baleen whales
following large-scale commercial exploitation have been linked to
interspecific competition, and this phenomenon has been implicated by
some observers in the apparent failure of some species to recover.  Here,
we examine the evidence for competition among mysticetes from an
ecological perspective, both generally and in two cases (blue and
northern right whales) for which competition has been cited as an
inhibitory factor.  We find little direct evidence of either of the
two generally recognized types of competition (exploitative and
interference).  That interference competition is rare is suggested by
the lack of territoriality in most species and the apparent absence
of agonistic interspecific interactions.  This is further supported
by ecological considerations of probable resource partitioning based
upon feeding apparatus and body size.  The hypothesis that changes in
biological and demographic parameters in Southern Ocean populations
reflect the occurrence of "competitive release" is intuitively
reasonable, but sufficient data on levels of prey biomass and predator
consumption are currently lacking, and the validity of many of the
purported changes is in question.  In addition, information on the
status of many populations is insufficient to confidently assess
whether or not recovery is occurring.  Although the potential for
exploitative competition exists, the influence of any form of
competition on recovery is currently impossible to determine: the
range of alternative explanations is too wide, and existing data
are too poor to allow us to discriminate among them.  Filling the many
gaps in our knowledge of this issue will be difficult, but such an
effort should be attempted if competition is to be considered or
excluded as a major factor affecting the recovery of exploited
populations.