Application of ADAPT-VPA to various stock hypotheses for the Antarctic minke whales distributed through IWC management areas IIIE to VIW

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University of Cape Town

This paper focuses primarily on addressing suggestions made during the Ulsan meeting of the Scientific Committee for refinement of the ADAPT-VPA assessments of Antarctic minke whales presented in Mori and Butterworth (2005). The methodology is extended to take account of different selectivities for the Russian and Japanese fleets during the period of commercial whaling, but this has little effect on results. The slopes of catch curves for the research catches have decreased and then stabilised during the course of the JARPA programme. This is indicative of a change in recruitment trends over time, rather than of a very high natural mortality as was amongst the postulates at the time of commercial whaling. ADAPT-VPA assessments are run for the five stock structure hypotheses specified by the Scientific Committee for the minke whales distributed through Areas IIIE to VIW, and for various choices of series of abundance estimates to which to fit the model. These runs generally indicate a trend of increasing recruitment of about 4% pa until the mid-1960s, followed by a trend in total abundance that decreases or is sometimes stable, depending on the abundance estimate series selected for fitting. Results for the Istock (Areas IIIE+IV+VW) are quite sensitive to this selection, but those for the P-stock (Areas VE+VIW) less so. Estimates of natural mortality M are generally in the 0.06 to 0.09 range, with a tendency to be somewhat higher for the P- compared to the I-stock. Fits of the outputs from the ADAPT-VPA to a stock-recruitment model generally require a carrying capacity for minke whales that first increased and then declined during the last century, and suggest MSYR1+ values in the 4-7% range. Possibilities for further work are outlined, including disaggregation of the analysis by sex.