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INT2021-03: Review of commercial fishing interactions with marine reptiles (PDF, 6,342K)

Summary

This project has updated and characterised protected marine reptile fishery captures in New Zealand waters to the 2021 fishing year. Five species of sea turtle (leatherback, green, hawksbill, loggerhead, and olive ridley) and four species of sea snake and kraits (yellow-lipped, Saint-Girons, blue-lipped, and yellow bellied) are known to occur in New Zealand waters and all are protected under the Wildlife Act 1953

Between 2007–08 and 2020–21, there were a total of 273 reported captures of turtles, an average of 19.5 per year, and one capture of a sea snake. Of these, 49 were recorded by Ministry observers. In commercial fishing returns, five species of turtles were reported, with leatherback being the most frequently captured (n = 217; 79.5%), following by green turtles (n = 25; 9.2%). In the observed records, 37 (76%) were leatherback turtles. Most captures, across all species, were made in the surface longline fisheries targeting bigeye tuna or swordfish in FMA 1 (northeast North Island), where such fishing effort was also greatest, largely between January and April. The single sea snake, a banded sea krait, was caught during bottom longline fishing targeting tarakihi. The turtle captures varied between 2–34 per year until 2020–21, when they increased to 58.

For the main turtle capture area and season, FMA 1 and January to April inclusive, between 2007–08 and 2020–21, most of the reported turtle captures (86.6%) were made by vessels which did not have an observer aboard. Of the 53 vessels in the selected fishery, 10 (18.9%) had reported turtle bycatch, and just five of the 10 reported 90.7% of the turtle captures, with one vessel alone reporting 38.7% of all captures. This vessel was only observed in 2020, when it accounted for 33.0% of the observed events, and 2021, when it accounted for 47.3% of the observed events. That observers were on this vessel in 2021, and the times and places that it fished, may partially explain why the observer turtle capture total was so much higher in 2020–21.

Evaluation of the environmental variables and the captures of leatherback turtles suggested the primary influence on turtle capture was likely to be water temperature, followed by frontal zones, ocean currents, and water clarity, with primary productivity having relatively little influence. Leatherback turtle captures were predicted to be most likely when sea surface temperatures were between about 14–22°C, when subsurface temperature at 200m was relatively warm, in the first two-thirds of the calendar year, when the mixed layer depth was relatively shallow, when time varying eastward currents were either negative or relatively strong, at latitudes south of about 42°S (i.e., west coast South Island), and when vessels were targeting swordfish.

Given the IUCN “vulnerable to critically endangered” status of these species, there is a need to reduce turtle captures in New Zealand fisheries. Overseas recommendations propose that an achievable turtle capture rate (all species combined) should be less than 0.019 turtles per 1000 hooks for surface longline fisheries. Averaged between 2008 and 2021, leatherback turtle capture rates alone were at least 0.019 turtles per 1000 hooks in FMA1 between January and April. A previous iteration of this work provided recommendations to better monitor marine reptile captures in New Zealand and to date, little progress has been made on any of these. It is highly recommended that these proposals are adopted, including the implementation and monitoring of a minimal sea turtle interaction rate; guidelines to reduce sea turtle mortality; revision of observer coverage allocation; improved data quality and reporting; and improved population information and research. Additional recommendations made here include the implementation of set capture limits (absolute captures) rather than catch rate limit, further collection of biological information, improved estimation of capture rates through communication with skippers, and further investigation of alternative data sources.

Publication information

Dunn, M.R.; Finucci, B.; Pinkerton, M.H.; Sutton, P. 2022. Review of commercial fishing interactions with marine reptiles. INT2021-03 final report by NIWA for Department of Conservation. 78 p.