Fishing for the facts: river dolphin bycatch in a small‐scale freshwater fishery in Bangladesh

• Published in: Animal conservation Vol. 23; no. 2; pp. 160 - 170
• Main Authors: Dewhurst‐Richman, N. I., Jones, J. P. G., Northridge, S., Ahmed, B., Brook, S., Freeman, R., Jepson, P., Mahood, S. P., Turvey, S. T.
• Format: Journal Article
• Language: English
• Published: London Wiley Subscription Services, Inc 01-04-2020
• Subjects: Aquatic mammals; Bycatch; Cetacea; Dolphins; Dolphins & porpoises; Fisheries; Fishers; Fishing; Fishing nets; Freshwater; freshwater cetaceans; Freshwater fish; Freshwater fishes; Freshwater mammals; Ganges River dolphin; gillnet; Gillnets; Inland water environment; interview data; local informant data; Man-induced effects; Marine mammals; Mortality; Mortality causes; Mortality risk; Platanista gangetica gangetica; Probability theory; Regulations; Rivers; Small-scale fisheries; Sustainability; Water depth; Whaling; Bangladesh
• ISSN: 1367-9430; 1469-1795
• DOI: 10.1111/acv.12523

Fisheries bycatch is a primary driver of cetacean declines, especially for threatened freshwater cetaceans. However, information on the factors influencing cetacean susceptibility to bycatch in small‐scale fisheries is limited, impeding development of evidence‐based conservation strategies. We conducted 663 interviews with fishers from southern Bangladesh to investigate the influence of net and set characteristics on seasonal bycatch rates of Ganges River dolphins Platanista gangetica gangetica and assess the sustainability of annual mortality levels. Between October 2010–October 2011, 170 bycatch events (and a minimum of 14 mortalities) were reported, 89% of which occurred in gillnets. The probability of bycatch increased as water depth declined, and as net mesh size increased. While the number of recorded bycatch incidents was higher in gillnets, risk of mortality was greater in set bagnets. Our mortality estimate indicates that fisheries‐related bycatch currently exceeds the sustainable limit recommended by the International Whaling Commission by 3.5 times. Numerous regulations have been developed to improve the productivity of commercially important fisheries, and if regulations were effectively enforced, these may also reduce river dolphin bycatch.
Fisheries bycatch is a primary driver of cetacean declines, especially for threatened freshwater cetaceans. We carried out interviews with fishers from southern Bangladesh to investigate the influence of fishing gear characteristics on bycatch rates of Ganges River dolphins Platanista gangetica gangetica, and to assess the sustainability of annual mortality levels. In one year, 170 bycatch events and 14 mortalities were documented, the majority in gillnets, which exceeds the sustainable limit for a population of this size by three and a half times. Numerous fishery regulations are already in place for economically important fish species that may also serve to reduce river dolphin bycatch.