Revised assessment for Oceania humpbacks: survey design considerations and power analysis

Carroll, Emma L.; Brooks, Lyndon; Burns, Dan; Jackson, Jennifer A. ORCID:; Baker, C. Scott; Clapham, Phillip; Constantine, Rochelle; Garrigue, Claire; Hauser, Nan; Mattila, David; Oremus, Marc; Poole, Michael; Robbins, Jooke; Steel, Debbie; Fewster, Rachel M.. 2013 Revised assessment for Oceania humpbacks: survey design considerations and power analysis. In: International Whaling Commission, Scientific Committee Annual Meeting.

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The Oceania population of humpback whales, comprising sub-stocks E2, E3, and F, was heavily depleted by whaling operations in the 20th century and is now classed as Endangered by the IUCN. A mark-recapture study of individuals identified by genotypes and photo-identification found the Oceania population had a superpopulation size of 4,329 whales (95% CL 3345, 5315) from 1999 to 2005 and an annual population growth (λ) for this period of 1.03 (95% CL 0.90-1.18). This low and imprecise estimate of growth contrasts with the high rate of growth for east Australia (10.9% per annum, corresponding to λ = 1.109; 95% CL 10.5%-11.3%) but the wide confidence intervals do not allow a firm trend to be detected. At a recent meeting of the South Pacific Whale Research Consortium (SPWRC), it was recommended that a future assessment of the Oceania humpback stock through mark-recapture methodology should be able to meet 3 objectives: (1) determine population size with a coefficient of variation (CV) of <20% and (2) detect if λ is significantly different from 1 (i.e. the population is increasing or decreasing) and (3) detect if λ is significantly different from that of east Australia. Here we make recommendations for the sampling design of future surveys and conduct a power analysis to see if the proposed surveys will meet the defined objectives. Simulations were undertaken for the combined regions of Oceania, in addition to individual wintering grounds of New Caledonia (NC: E2) and Tonga (TG: E3). The proposed survey designs include a capture probability of p=0.10 for new surveys and target the three core regions of New Caledonia, Tonga and French Polynesia. We recommend conducting surveys that span the wintering period to reduce heterogeneity in capture probability due to the difference in migratory timing between demographic classes. Under the simulated scenarios for Oceania, incorporating data from the previous genotype surveys from 1999-2005 with three new survey years will give sufficient power to meet objective 1, detect if the growth rate is significantly lower than that of east Australia if the true λ ≤1.05 and detect if the growth rate is significantly >1 if the true λ=1.05. The simulations also suggest that the power to meet the objectives on a regional basis varies with the survey design and simulated scenario. However, in general, the biennial survey design was able to detect with ≥90% power if the growth rate is significantly lower than that of east Australia if the true λ ≤1.03 for both NC and TG. Therefore, it seems the proposed surveys would allow us to test whether population growth rates in these different regions are significantly different: this appears to be important given the recent rapid increase in the New Caledonian calving ground.

Item Type: Publication - Conference Item (Paper)
Programmes: BAS Programmes > Polar Science for Planet Earth (2009 - ) > Environmental Change and Evolution
Additional Information. Not used in RCUK Gateway to Research.: Paper SC/65A/SH09
Date made live: 04 Mar 2014 09:34 +0 (UTC)

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