Life in the Slow Lane: Ecology and Conservation of Long-Lived Marine Animals

<em>Abstract.</em> —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 (below 19°S) and mainly during winter and spring ( July to September). Occasional sightings of humpbacks in northern GBR waters (above 16°S) in summer supports previous claims of a substock resident year-round in northern Australian tropical waters. Mother–calf sightings were rare with most recorded below 21°S 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% confidence interval [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% to 5.7%)—a finding consistent with an estimate of low and variable juvenile recruitment.