Subject: Abstract: humpback seasonal abundance and survival probabilities (fwd)

Mike Williamson (pita@www1.wheelock.edu)
Sat, 14 Aug 1999 13:27:58 -0400 (EDT)

Date: Fri, 13 Aug 1999 13:37:04 -1000
From: Pacific Whale <pwhale6@maui.net>
Reply-To: research@pacificwhale.org
To: MARMAM@UVVM.UVIC.CA
Subject: Abstract: humpback seasonal abundance and survival probabilities

Chaloupka, M., M. Osmond and G. Kaufman. 1999. Estimating seasonal
abundance trends and survival probabilities of humpback whales in Hervey
Bay (east coast Australia). Marine Ecology Progress Series 184:291-301.

Milani Chaloupka*

*Present address: Dept. of Zoology and Entomology, University of
Queensland, St. Lucia, Queensland 4067, Australia. E-mail:
m.chaloupka@mailbox.uq.edu.au


ABSTRACT: The abundance of east Australian Group V substock (EAGVS)
humpback whales resident during winter in Hervey Bay was estimated from
a 10 yr mark-resight study using photo-identification of 969 individual
humpbacks sighted between 1987 and 1996. Hervey Bay is on the east coast
of Australia and is the major southbound  stop-over site for humpbacks
returning to Antarctic waters from overwintering in Great Barrier Reef
(GBR) waters. Seasonal abundance estimates were derived from
mark-resight profiles using a reduced form Cormack-Jolly-Seber (CJS)
model (constant survival, time-varying resight likelihood) that fitted
the data well. The bootstrap mean CJS abundance estimate over the 9 yr
period from 1988 to 1996 was 855 (95% CI: 750 to 936). Estimated
humpback abundance in Hervey Bay showed significant temporal variability
superimposed on an increasing linear trend estimated using times series
regression model bootstrapping at 6.3% yr-1 (95% CI: 2 to 11%). The
seasonal Hervey Bay population comprised 30 to 50% of the EAGVS
southbound to Antarctic feeding grounds. Estimated abundance increased
from 554 post-yearling humpbacks in 1988 to a peak of 1040 in 1991
before declining to 921 by the mid-1990s. Standard errors of abundance
estimates suggested good precision and were derived using a variance
components approach that separated sampling error from ecologically
relevant variation. The trends in temporal variability and annual rate
of humpback abundance increase were consistent with findings from an
aerial surveillance study (1982 to 1996) of monthly sightings of the
EAGVS overwintering in  southern GBR waters. The concurrence of findings
from an independent method of abundance estimation provides confidence
in the CJS model used in this study to estimate abundance. Post-yearling
survivorship was estimated from a 4 yr (1993 to 1996)
photo-identification study of 517 individual humpbacks sighted at 2
seasonally  sequential overwintering sites (Hervey Bay, Whitsundays)
using a robust design CJS modelling approach with estimators that
account for bias due to temporary emigration. A reduced form CJS model
(constant survival, time-varying resight likelihood) also fitted the
data well with the mean annual survival rate for the EAGVS humpbacks
estimated at 0.966 (95% CI: 0.87 to 1.00). The good fit of the robust
design survival rate model provides further confidence in the Hervey Bay
abundance model, which suggests that the EAGVS has been recovering but
at a slow and variable rate.



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