4.3 Article

Setting the net lower: A potential low-cost mitigation method to reduce cetacean bycatch in drift gillnet fisheries

Journal

AQUATIC CONSERVATION-MARINE AND FRESHWATER ECOSYSTEMS
Volume 31, Issue 11, Pages 3111-3119

Publisher

WILEY
DOI: 10.1002/aqc.3706

Keywords

CPUE; fisheries; incidental capture; mitigation; small cetaceans; tuna

Funding

  1. Australian Marine Mammal Centre, Government of Australia
  2. Engro Foundation
  3. FAO/GEF/Common Oceans Project Areas Beyond National Jurisdiction
  4. Indo-Pacific Cetacean Research and Conservation Foundation
  5. Shark Conservation Fund

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Bycatch is a significant threat to marine megafauna worldwide, particularly leading to the decline of cetacean species. High levels of bycatch have been documented in the Indian Ocean's gillnet fisheries for the past two decades. Efforts to reduce bycatch are limited by availability, cost, and social acceptability, highlighting the need for further research and mitigation methods in the fishing industry.
Bycatch is the most significant threat to marine megafauna (sea turtles, marine mammals, elasmobranchs, seabirds) worldwide, and the leading cause of the decline of several cetacean species. The bycatch issue in the Indian Ocean is poorly understood, but high bycatch levels in gillnet fisheries have been documented for the past two decades, in both small-scale and semi-industrial fisheries. Unfortunately, methods to reduce bycatch are often unavailable, financially non-viable or socially unacceptable to fishermen. Using a network of trained boat captains in the tuna drift gillnet fishery in the Arabian Sea, targeted catch and bycatch data were collected from 2013 to 2017 off the coast of Pakistan (northern Indian Ocean). Two fishing methods using multifilament gillnets were used: surface deployment and subsurface deployment (i.e. headline of net set below 2 m depth). Predicted catch rates for targeted species did not differ significantly between the two fishing practices, although a drop in tuna (6.2%) and tuna-like (10.9%) species captures was recorded in subsurface sets. The probability of cetacean bycatch, however, was 78.5% lower in subsurface than in surface sets. Cetacean bycatch in tuna drift gillnet fisheries has the potential to be significantly reduced at a relatively low cost for fishers. However, further research with an appropriate sampling design and a large sample size is required to confirm the efficacy of the proposed mitigation method. The acceptability and adoption of subsurface setting by fishers also needs to be further investigated. Despite some limitations, this preliminary study also highlights the importance of crew-based observer data as an alternative source of data when observers cannot be deployed on fishing vessels.

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