Exploring the assumptions of multi-stock assessment models for humpback whales ( Megaptera novaeangliae ) in the Southern Hemisphere: using Breeding Stocks D and E as an example

• Main Authors: Leaper, R, Peel, S, Peel, D, Gales, N
• Format: Article in Journal/Newspaper
• Language: English
• Published: International Whaling commission, Cambridge, UK 2011
• Subjects: Biological Sciences; Ecology; Marine and Estuarine Ecology (incl. Marine Ichthyology); Butterworth; Humpback Whale; Megaptera novaeangliae
• Online Access: http://www.iwcoffice.org/JCRM.htm; http://ecite.utas.edu.au/75512

There is potential value in exploring multi-stock models to address situations where humpback stocks are mixing. However, sensitivity to theassumptions underlying these models has yet to be fully explored. Using a simple simulation approach, the assumptions of a population model thatallows for mixing of humpback whale (Megaptera novaeangliae) stocks D and E on feeding areas has been explored by relaxing the assumptionsof the original Johnston and Butterworth model in a number of plausible ways. First the ability of the model to estimate parameters was checkedfor a situation where simulated data are generated from an underlying model of exactly the same form for which the actual values of these parametersare known (Scenario 1). Then the ability of the model to estimate these parameters when alternative forms and assumptions were used for theunderlying model generating the data was investigated. Specifically, stocks were allowed to mix non-uniformly across each feeding area and catchwas non-uniformly distributed across each feeding area (Scenario 2). The consequences of density dependence implemented on feeding rather thanbreeding areas (Scenario 3) were also examined. The original mixing model was robust to alternate mixing and catch allocation scenarios in all butone of the simulations, but when density dependence acted at the level of the feeding rather than the breeding areas, the model produced estimatesthat were quite different from the underlying population. It is recommend that the inclusion of density dependence on feeding areas in models thatallow for mixing of whales on these grounds be investigated further