A REVIEW OF THE METHODS USED TO RELEASE SKATES (RAJIIDS), WITH OR WITHOUT TAGS, IN ANTARCTIC EXPLORATORY FISHERIES

An ongoing mark and recapture experiment for skates was commenced by New Zealand fishing vessels in the Ross Sea (CCAMLR Subareas 88.1 and 88.2) in 1999/2000. Based on preliminary results from this programme showing an unquantifiable degree of the survivorship of returned skates, the CCAMLR Scientific Committee gave approval in 2004 for licensed vessels to cut live skates from the line (while in the water) as an alternative to either retaining all aboard or discarding dead skates, as a skate mortality mitigation measure. Initial opinion when the skate tag and recapture programme was first implemented was that some form of in-water release would be the ideal to improve survival chances. Subsequently a number of problems have become evident with this method. The Working Group on Fish Stock Assessment (WG-FSA) noted in 2004, when recommending skate release as an option to the Scientific Committee, that it might be difficult to detect tagged rays skates if they are cut off at the sea surface rather than being brought on board. The WG-FSA recommended that should the tag identification rate be low, a relaxation of the requirement to cut all rajids from the line on specified vessels and/or for specified time periods be adopted. Consistent with this recommendation, commencing in the 2006/07 season, New Zealand fishing vessels were given permission by the New Zealand government as part of the national research plan, to trial an alternative technique. The new method (for simplicity in this paper called Method 2), required the crew to bring the skate aboard carefully, remove the hook and snood, take and record biological (and potentially other meristic data) from a sub-sample when possible, and release live skates in a timely fashion in a manner most likely to ensure survival. The advantages of this method have been the more effective scanning of the captured skate for existing tags, greater accuracy in the assessment of ideal candidates for live release, the capability to collect supporting meristic and biological data for release candidates, correct species and sex identification, and the ability to more accurately place tags on the skate body – improving the quality of skate tagging. Following favourable results aboard by New Zealand vessels using Method 2 during the 2006/07 season and following a discussion and recommendation from WG-FSA 2007 an amendment to CM 33-03 (2007) was made stating that: ‘Unless otherwise requested by scientific observers, vessels, where possible, should release skates and rays alive from the line by cutting snoods, and when practical, removing the hooks’. This paper documents the evolution of skate release methods both for tagging and for live release for New Zealand autoline vessels. It describes the current Method 2 systems in use for two New Zealand vessels. A brief analysis based on data collected from the skates treated in this manner during the 2007/08 fishery in the Ross Sea is included in the document to highlight the additional advantages in data collection possible using Method 2. This paper is intended to inform WG-FSA with additional information collected over the last two fishing seasons in preparation for the ‘Year of the Skate’ prior to a final decision on skate release protocols. A proposal is made for a comparative experiment using two tag types to inform a final decision on a standardised CCAMLR tag type for Rajid mark and recapture programmes carried out within CCAMLR Dissostichus spp. exploratory fisheries.