Subject: Abstract: Decline of Galapagos sperm whales (fwd)

Mike Williamson (pita@www1.wheelock.edu)
Tue, 17 Feb 1998 15:26:36 -0500 (EST)

From:  Hal Whitehead, Department of Biology, Dalhousie University,
Halifax, Nova Scotia, CANADA B3H 4J1

email: hwhitehe@is.dal.ca

Whitehead, H., J. Christal and S. Dufault.  1997.  Past and Distant
Whaling and the Rapid Decline of Sperm Whales off the Galapagos
Islands.  Conservation Biology.  11: 1387-1396

Abstract:  It is generally expected that exploited whale populations
should rebuild following the end of whaling.  Using photographic
identification of individuals during a series of field projects, we
studied female and immature sperm whales (Physeter macrocephalus) that
visit the waters off the Galapagos Islands, Ecuador.  Analysis of
mark-recapture data, using a likelihood model, indicates that the
population decreased at a rate of about 20% per year (95% c.i. 7-32%)
between 1985-1995.  During this period the animals were not being
hunted and were not obviously the subject of other immediate
anthropogenic threats.  Rates at which research vessels encountered
whales also fell over this interval.  The decline seems to be due
principally to migration into waters off the Central and South
American mainland.  The population also has a very low recruitment
rate, about 0.05 calves/female/year, as indicated by rates of
observation of calves.  Although other causes cannot be completely
ruled out, both the high emigration rate and low recruitment rate are
probably related to heavy whaling in Peruvian waters which ended in
1981.  Whales from the Galapagos are moving east to fill productive
but depopulated waters near the coast, and the virtual elimination of
large breeding males (in their late twenties and older) from the
region has lowered pregnancy rates.  The case of the Galapagos sperm
whales strongly suggests that exploitation can continue to have
substantial negative impacts on the size and recruitment rate of an
animal population well outside the range of the hunt and for at least
a decade after it has ended.