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