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A plausible range of MSYR(1+) and relative plausibility of stock structure hypotheses for the WNP common minke whales investigated by bycatch data: Updated responses to requests by the Scientific Committee for more detailed explanation for Section 4 of SC
Toshihide Kitakado and Mutsuo Goto
International Whaling Commission
2018
SC/67B/RMP/02
This paper aims at suggesting a plausible range of MSYR(1+) and relative plausibility of stock structure Hypotheses A and C for the western North Pacific common minke whales by responding to comments made in SC67a for more detailed explanation for Section 4 of SC/67a/SCSP/13. First, as supplementary information, the paper begins showing time trajectory of population size for each stock under the two stock structure hypotheses. Then an estimated time trend of bycatch proportion of J animals is given with a set of formulas as requested by the SC, and this is compared to that estimated in RMP/IST trials under different assumptions for stock structure (Hypotheses A and C) and MSYR. The results show that only an MSYR(1+) value of 2% or more under Hypothesis A is consistent with the bycatch data, for which the results discussed above indicate no conservation concern for the J stock under the research catches to be taken by Japan. These conclusions are robust to different specifications of the error structure for the time trend estimate from the bycatch data. Also, the results were not sensitive to handling of unassigned J/O animals. However, there are discrepancies between data and model predictions at a sub-area level, which points to the need to revise the mixing matrices used for the RMP/IST trials.
