WCPFC Shark Post-Release Mortality Tagging Studies

Common Oceans (ABNJ) Tuna Project (2017) WCPFC Shark Post-Release Mortality Tagging Studies. In: WCPFC Scientific Committee 13th Regular Session. WCPFC-SC13-2017/EB-IP-06, Rarotonga, Cook Islands

The first of two workshops related to this study convened an expert panel of academic, government, and non-government scientists from around the world representing over 100 years of shark tagging expertise. The primary objective of the expert panel was to prepare and agree a survey design which would have optimal scientific rigor, cost-effectiveness and consistency with past and ongoing work. The report of the expert panel is appended to this covering note and describes how and why the panel decided to focus the tagging work on silky and shortfin mako sharks in longline fisheries. Oceanic whitetip shark was identified as being a species of interest but it was agreed that low catch rates make it unlikely that this study could obtain enough samples and that different tag types and tagging procedures would be preferred for this species. WCPFC and SPC, with assistance from tagging coordinators from NIWA, are now implementing the study following the expert panel's recommendations. The study has benefitted immensely in its first phase from the cooperation of the New Zealand Ministry for Primary Industries (MPI) which volunteered five experienced observers to be trained and to attach the tags, and helpfully convened a stakeholders meeting to kick-off the project in New Zealand. As of 30 June 2017, 21 survival pop-up archival tags (sPATs) have been attached to shortfin mako sharks by observers in the New Zealand longline fishery. Another 14 are awaiting attachment, and ten of these have already been distributed to the observers. Tagged sharks have ranged from 0.9-2.5 m in length. Unfortunately, six tags have popped-up prematurely, but tag data as of 30 June 2017 indicate that sharks were tracked for as many as 36 days before pop-up with all moving north and some transiting considerable distances (Figure C1). In addition to the tag that recorded movements for 36 days, three other tags have remained attached to sharks for over a month but had not reported as of 30 June 2017. These tracks will provide us with not only an indication of survival (i.e. no post-release mortality), but the added benefit of habitat and range information, for this species (Figure C1). In parallel with the completion of the New Zealand tagging work on shortfin mako shark, in phase two we intend to transition the operations to Fiji, home to one of the region's largest longline fleets catching both shortfin mako and silky sharks. We are currently discussing Fiji’s participation with both the Fiji Ministry of Fisheries and an industry partner, and we sincerely appreciate the interest and enthusiasm they have shown thus far. The expert panel advised that the Fiji fleet may not be representative of the larger freezer longliners operating in the equatorial region, and suggested another national observer programme which can serve as a proxy for those vessels, such as the Federated States of Micronesia or the Republic of the Marshall Islands, also be engaged later in the study. Another possibility may be tagging in Tonga as the fishery there, as in Fiji, has relatively high catch rates for both shortfin mako and silky sharks. Tags that cannot be deployed in these fisheries may be offered to an ongoing United States government programme tagging oceanic whitetip sharks in American Samoa.