Accidental by-catch in fishing nets is estimated to kill 300,000 whales, dolphins and porpoises every year. Porpoises are air-breathing mammals, so once they become stuck in a net, they only have minutes before they drown.
Active fishing gear is just as dangerous as abandoned gear. “Ghost nets”, forgotten or abandoned at sea by fishermen, are particularly difficult to detect. They can continue to catch fish, seabirds and even larger mammals like the vaquita a long time after they are abandoned. The weight of a full net lets it sink to the bottom where the fish caught in the net are consumed by bottom-dwelling crustaceans or other fish. The empty net then floats to the surface where the cycle continues.
References and Further Reading
- Trippel, E. A. ; Shepherd, T. D. (2004). By-catch of harbour porpoise (Phocoena phocoena) in the lower Bay of Fundy gillnet fishery, 1998–2001. Canadian Technical Report of Fisheries and Aquatic Sciences.
- Tonay, Arda M. (2016). Estimates of cetacean by-catch in the turbot fishery on the Turkish Western Black Sea Coast in 2007 and 2008. Journal of the Marine Biological Association of the United Kingdom.
- Trippel, Edward A. ; Strong, Michael B. ; Terhune, John M. ; Conway, Jeremy D. (1999). Mitigation of harbour porpoise (Phocoena phocoena) by-catch in the gillnet fishery in the lower Bay of Fundy. Canadian Journal of Fisheries and Aquatic Sciences.
- LORENZO ROJAS-BRACHO ; RANDALL R. REEVES ; ARMANDO JARAMILLO-LEGORRETA (2006). Conservation of the vaquita Phocoena sinus. Mammal Review.