Marine Mammals

Marine mammals may be accidentally captured in purse seines. They may also become entangled in longlines or or hooked on them, e.g., false killer whales in the Hawaii-based deep-set longline fishery. In the tropical tuna purse-seine fishery, species such as baleen whales or dolphins (as well the whale shark Rhincodon typus), may serve as sighting cues by purse-seine fishermen for the presence of tuna schools at the surface of the sea and/or may be caught accidentally when fishing for the targeted species [1].

Successful techniques to release marine mammals from purse seine nets have been employed for some time, e.g., the backdown procedure and Medina panel, and there have been advances in techniques for safe handling and release of megafauna from purse seines [2,3]. Progress in the development of dynamic spatial fishery management strategies will help fishers to avoid interactions in the first place. For example, a recent study identified the principal environmental variables influencing the co-occurrence between baleen whales, whale sharks and tuna purse-seine fisheries [1]. Fishing area closures are utilised in the interim. 'Weak' circle hooks and strong branchlines are required in the Hawaii-based deep-set and shallow-set longline fisheries (see NOAA's Whale link below). They can reduce bycatch (but not depredation), though post-interaction mortality is unknown.

SeaLlifeBase is a source of biological and distribution data for marine mammal species. FAO's guide to the Marine Mammals of the World provides species identification and distribution information. Locate handy Species ID guides here. NOAA's 'Find a Species - Dolphins & Porpoises' and 'Whales' has information on protection status, biology and population status, distribution, threats, conservation measures and research.

References