Estimating seasonal abundance trends and survival probabilities of humpback whales in Hervey Bay (east coast Australia)

The abundance of east Australian Group V substock (EAGVS) humpback whales resident dunng winter in Hervey Bay was est~mated from a 10 yr mark-resight study using photo-identdication of 969 individual humpbacks slghted between 1987 and 1996 Hervey Bay is on the east coast of Austraha and is the major southbound stop-over s ~t e for humpbacks returning to Antarctic waters from overwintenng 111 Great Barner Reef (GBR) waters Seasonal abundance estimates were denved from mark-resight profiles using a reduced forin Cornlack-Jolly-Seber (CJS) model (constant survival timevarying 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"1, C1 750 to 936) Estimated humpback abundance in Hervey Bay showed signif~cant temporal variability superimposed on an increasing linear trend estimated using tlmes series regression model bootstrapping at 6 3 % yr ' (95 % C1 2 to 11 %) The seasonal Hervey Bay population comprised 30 to 50°( of the EAGVS southbound to Antarctic feeding grounds Estlrnated abundance increased from 554 post-yearling humpbacks in 1988 to a peak of 1040 in 1991 before dechning to 921 by the mid-1990s Standard errors of abundance estimates suggested good precision and were derived using a vanance components approach that separated sampling error from ecologically relevant var~ation The trends In temporal vanability and annual rate of humpback abundance increase were consistent with findings from an aerial surve~llance study (1982 to 1996) of monthly sight~ngs of the EAGVS overwinterlng In southern GBR waters The concurrence of findings from an independent method of abundance est~mation provides confidence in the CJS model used in this study to estlmate abundance.Post-yearhng 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 emigrat~on.A reduced form CJS model (constant survival, timevarying reslght 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.K E Y WORDS.Humpback whales .