Potential implications of the choice of longline mitigation approach allowed within CMM 2014-05

Harley S, Pilling GM (2016) Potential implications of the choice of longline mitigation approach allowed within CMM 2014-05. WCPFC, Bali, Indonesia

This paper extends the analyses described in WCPFC-SC11-2015/EB-WP-02 on the potential impact of several longline gear restrictions of fishing-related mortality on oceanic whitetip shark and silky shark. Specifically, this paper attempts to assess the potential impacts of fleet choice that CMM2014-05 “Conservation and Management Measure for sharks” allows on longline mitigation approaches for these two shark species.
Using Monte Carlo simulations we compare the outcomes of “status-quo” fishing where use of (1) wire-trace material 3and (2) shark-lines continues at currently observed levels, with scenarios where each are excluded, either individually or combined, and with scenarios where individual flag-states either choose to exclude the gear they use most frequently, or the gear they use least frequently.
The key conclusions of the analyses are:
1. The option for flag states to choose which fishing technique they exclude (either wire trace or shark-lines) has the potential to greatly reduce the benefits to silky shark and oceanic whitetip shark; and
2. If flag-states choose to exclude the technique least used by their vessels, the median predicted reductions in fishing-related mortality are 6% for silky shark and 10% for oceanic whitetip shark. This compares to reductions of 24% and 37% respectively if choice was removed and both techniques excluded.
We invite SC12 to consider these findings in their evaluation of the effectiveness of the shark CMM 2014-05. We also reiterate some of the important areas for knowledge improvement previously detailed in WCPFC-SC11-2015/EB-WP-02; e.g. further details of fishing gear configurations used, and research into likely rates of release mortality.