Cetacean interactions with pot fisheries

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Summary

Cetacean entanglements have occurred globally in pot and trap fishing gear for decades. Entanglements typically occur in the vertical ropes connecting the pot/trap to a position marker (such as a buoy or float) at the sea surface. Entanglements can result in injuries and mortalities, with negative consequences for both animal welfare and potentially cetacean population persistence. Methods to reduce cetacean interactions with pot and trap fishing gear, and the impacts of entanglements, include gear modifications, spatial/temporal management,
and disentanglement interventions. In New Zealand waters, cetacean entanglements with pot fishing gear have
been documented since 1980. From 1980 to the present, 1-2 entanglement events per year have been reported on average. However more recently, from 2010 – 2020, an average of 4-5 entanglement events per year have been recorded. Disentanglement interventions are the main documented approach to addressing this issue in New Zealand to date.

In this project, we update previous work on cetacean entanglements in New Zealand waters. We consider spatial and temporal trends in pot fishing effort, and entanglement information held by the Department of Conservation. We also review recent entanglement mitigation information and consider mitigation and management methods investigated in other jurisdictions. Further, we convened a workshop of expert stakeholders to share information, better understand entanglement risks and issues in the New Zealand rock lobster fishery, and proactively consider how to manage the entanglement issue with industry involvement. In New Zealand waters, pot fishing occurs in all Fisheries Management Areas except FMA 10 (Kermadec). Fishing effort reported has declined significantly from 1990 to 2021, with this decline driven by a reduction in
pot fishing effort targeting rock lobster (Jasus edwardsii). Pot fishing targeting other species represents <10% of effort on average. Other species targeted with this method include packhorse lobster (Jasus verreauxi), ling (Genypterus blacodes), blue cod (Parapercis colias), paddle crab (Ovalipes catharus), and hagfish (Eptatretus cirrhatus). Pot fishing occurs around the main islands of New Zealand, and the Chatham Islands, with effort varying monthly among target species. Pot soak times vary within and between target species. Since 1980, entanglements in pot fishing gear have been detected along the north-east coast of the North Island, Cook Strait and Marlborough, east coast of the South Island, and Fiordland and Stewart Island. Most recorded entanglements over time have involved humpback whales (Megaptera novaeangliae; 62%), followed by orca
(Orcinus orca; 16%). Most entanglements have been reported in June, with almost all of these involving humpback whales. Orca entanglements have occurred in the spring and summer months. Entanglement events involving other cetacean species comprise 22% of those reported, and have occurred occasionally through the year. Ecological factors relevant to entanglements are generally not well understood. However, the migration of humpback whales along the New Zealand coast continues to be a higher risk period based on entanglement reports. The fishing gear type most recently described in entanglement reports is ‘cray’ (rock lobster). Recent literature showed a breadth of work on entanglement mitigation and management. Approaches included gear-associated measures (gear modifications, acoustic deterrents and ropeless fishing), spatial and temporal closures, and investigations of whale ecology to understand and account for distribution and entanglement risks.

We identified a range of possible actions to build understanding, investigate and manage cetacean
entanglement risks in New Zealand pot fisheries. These include improving reporting of entanglement events and pot soak times, growing knowledge of cetacean distribution (spatial and temporal), characterising gear in use in rock lobster and other pot fisheries, fostering the adoption of straightforward low/no cost mitigation approaches, and testing two technical mitigation methods (galvanic timed releases and rope segments) that are used internationally under local conditions.

Publication information

Pierre, J. P., How, J. R., Dunn, A. 2022. Whale entanglements with New Zealand pot fisheries: characterisation and opportunities for management. MIT2021-02 final report prepared by JPEC for Department of Conservation, Wellington. 79 pp.