- Superpopulation capture–recapture models are useful for estimating the
abundance of long-lived, migratory species because they are able to account for the fluid
nature of annual residency at migratory destinations. Here we extend the superpopulation
POPAN model to explicitly account for heterogeneity in capture probability linked to
reproductive cycles (POPAN-τ). This extension has potential application to a range of species
that have temporally variable life stages (e.g., non-annual breeders such as albatrosses and
baleen whales) and results in a significant reduction in bias over the standard POPAN model.
We demonstrate the utility of this model in simultaneously estimating abundance and annual
population growth rate (λ) in the New Zealand (NZ) southern right whale (Eubalaena
australis) from 1995 to 2009. DNA profiles were constructed for the individual identification
of more than 700 whales, sampled during two sets of winter expeditions in 1995–1998 and
2006–2009. Due to differences in recapture rates between sexes, only sex-specific models were
considered. The POPAN-τ models, which explicitly account for a decrease in capture
probability in non-calving years, fit the female data set significantly better than do standard
superpopulation models (DAIC . 25). The best POPAN-τ model (AIC) gave a superpopulation
estimate of 1162 females for 1995–2009 (95% CL 921, 1467) and an estimated
annual increase of 5% (95% CL -2%, 13%). The best model (AIC) gave a superpopulation
estimate of 1007 males (95% CL 794, 1276) and an estimated annual increase of 7% (95% CL
5%, 9%) for 1995–2009. Combined, the total superpopulation estimate for 1995–2009 was
2169 whales (95% CL 1836, 2563). Simulations suggest that failure to account for the effect of
reproductive status on the capture probability would result in a substantial positive bias
(+19%) in female abundance estimates.
- Carroll, E. L., Childerhouse, S. J., Fewster, R. M., Patenaude, N. J., Steel, D., Dunshea, G., . . . Baker, C. S. (2013). Accounting for female reproductive cycles in a superpopulation capture-recapture framework. Ecological Applications, 23(7), 1677-1690. doi:10.1890/12-1657.1
|Funding Statement (additional comments about funding)
- The 1995–1998 AucklandIslands field trips were funded by the Whale and DolphinConservation Society, the U.S. Department of State (Programfor Cooperative US/NZ Antarctic Research), the AucklandUniversity Research Council, and the New Zealand MarsdenFund. Biopsy samples were collected during the 2006–2009 fieldseasons under DOC Marine Mammal Research permit andUniversity of Auckland Animal Ethics Committee approvedprotocol to C. S. Baker. The 2006–2009 field seasons werefunded by aWinifred Violet Scott Estate Research Grant Fund,Australian Antarctic Division, Marine Conservation ActionFund, Blue Planet Marine NZ Ltd, Holsworth WildlifeResearch endowment, New Zealand Ministry of ForeignAffairs, DOC, South Pacific Whale Research Consortium,National Geographic, and Brian Skerry Photography. Lab work was funded by the NZMarsden Fund, DOC, the Heseltine Trust, and an OMV NZLtd. Scholarship to E. Carroll. E. Carroll was supported by aTertiary Education Commission Top Achiever Scholarship andthe School of Biological Sciences, University of Auckland.
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