Subject: Feed:Competition in baleen whales (fwd)

Mike Williamson (pita@www1.wheelock.edu)
Mon, 15 Sep 1997 08:05:01 -0400 (EDT)

---------- Forwarded message ----------
Date: Sat, 13 Sep 1997 09:30:24 -0400
From: Phil Clapham <CLAPHAMP@NMNH.SI.EDU>
Reply-To: Marine Mammals Research and Conservation Discussion
     <MARMAM@UVVM.UVIC.CA>
To: MARMAM@UVVM.UVIC.CA
Subject: Competition in baleen whales

Regarding the contention (made in the WSJ op-ed on whaling) that
species such as minkes need to be taken in order to permit supposedly
disadvantaged competitors (such as blue whales) to recover:

I would direct interested readers to a review that we wrote on this topic:

Clapham, P.J. & Brownell, R.L., Jr.  1996.  Potential for interspecific
competition in baleen whales.  Reports of the International Whaling
Commission 46: 361-367.

For convenience, I reproduce here the abstract:

  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 likely 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 recovery of exploited populations.


Phil Clapham


Phillip J. Clapham, Ph.D.
Smithsonian Instiitution
NHB 390, MRC 108
Washington, DC 20560
claphamp@nmnh.si.edu