Subject: Abstract: humpback distribution in the Great Barrier Reef (fwd)

Mike Williamson (pita@www1.wheelock.edu)
Sat, 21 Aug 1999 16:06:24 -0400 (EDT)

Date: Fri, 20 Aug 1999 11:44:07 -1000
From: PWF Research <research@pacificwhale.org>
To: MARMAM@UVVM.UVIC.CA
Subject: Abstract: humpback distribution in the Great Barrier Reef

Chaloupka M, Osmond M (1999) Spatial and seasonal distribution of
humpback whales in the Great Barrier Reef region. In: Musick JA (ed)
Life in the slow lane: ecology and conservation of long-lived marine
animals. American Fisheries Society Symposium 23: 89-106

The spatial and seasonal distribution of humpback whales in the Great
Barrier Reef Marine Park (GBRMP) was defined using data from a
systematic aerial surveillance program. The data comprised 414 pod
sightings (812 individuals) recorded from July 1982 to March 1996.
These sightings were supposedly of humpbacks from the east Australian
Group V substock that migrates during the austral autumn from
Antarctic feeding grounds to winter breeding grounds in GBR waters.
Humpbacks were sighted in all months and throughout the GBRMP.
However, most pods (75%) were sighted in southern GBR waters (>19oS)
and mainly during winter and spring (July-September). Occasional
sightings of humpbacks in northern GBR waters (<16oS) in summer
supports previous claims of a substock resident year-round in
northern Australian tropical waters. Mother-calf sightings were rare
with most recorded >21oS and mainly in August and September. These
limited sightings suggest that the main calving grounds for the east
Australian Group V substock occur in the extensive southern GBR
lagoonal waters defined northward by the Whitsunday Group of islands
and reefs and eastward by the Pompey/Swains reef complex. An estimate
of the crude birth rate was 0.072 (95% CI: 0.06 - 0.11) with Monte
Carlo estimates of the median calving rate at 0.3 calves per mature
female per year (95% CI: 0.22 - 0.43) and the median interbirth
interval at 3.4 years (95% CI: 2.3 - 4.5) indicating low and variable
juvenile recruitment. Nonparametric time series analysis (seasonal
and trend decomposition using loess, STL) of monthly humpback
sightings showed that the long-term trend in sightings was increasing
but that there was significant inter-annual variability in the
seasonal abundance of humpbacks in the GBRMP. The STL analysis also
suggested that the frequency of sightings increased earlier in winter
(June) and later in the season during spring/summer (October to
December). Time series regression analysis of the STL-derived trend
in sightings suggested that the east Australian Group V substock
increased slowly in abundance over the 14 years from 1982 to 1996 at
about 3.9% per year (95% CI: 1.9% - 5.7%) - a finding consistent with
an estimate of low and variable juvenile recruitment.

Reprints will be available from the senior author at:
m.chaloupka@mailbox.uq.edu.au


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