Good practices to reduce the mortality of sharks and rays caught incidentally by the tropical tuna purse seiners.

Poisson F, Vernet AL, Seret B, Dagorn L (2012) Good practices to reduce the mortality of sharks and rays caught incidentally by the tropical tuna purse seiners. EU FP7 project #210496 MADE, Montpellier, France

During the last decade, particular attention has been paid worldwide to the problem of bycatch and discards in fisheries. The MADE project funded by the seventh framework programme of the European Union, was set up to develop measures to mitigate the adverse impacts of fisheries targeting large pelagic fish in the open ocean: purse seiners using fish aggregating devices (FADs), and longliners.
Among the species that are accidentally caught by purse seiners, sharks and rays are particularly vulnerable. The life traits of sharks and rays (slow growth rates, late maturation, long gestation, low fecundity and long lives) make them highly susceptible to overfishing and efforts should be made to reduce their mortality. This specific issue is an objective of the ecosystem approach to fisheries and a request by consumers.
In addition, releasing bycatch alive in good conditions could facilitate the re-colonization process of the FAD after fishing. Indeed, sharks, and to a lesser extent rays, are usually considered by fishers as tough animals and they assume that they can easily survive when returned to the sea. Nevertheless some sharks that appear healthy upon release may die later because of injuries caused not only by the fishing process itself but also by handling practices. A preliminary study indicated that 50% of sharks died after release. It is therefore important to know what practices can cause a delayed mortality and which ones minimize physical trauma and stress to the animals. This manual, dedicated to skippers and crew of the tropical tuna purse seiners, shows good and bad practices when releasing sharks and rays.
Sharks and rays are not by nature aggressive, but they can certainly cause injuries to the crew. Sharks can bite or rays can sting humans in self-defence when threatened. Massive animals like whale sharks or large manta rays are very powerful and can therefore be dangerous to handle on board. For these reasons, safety of the crew has been considered as a priority in this guide. This manual provides information on the biology of sharks and rays and also includes guidelines to release sea turtles and also provides information for reporting catches of tagged animals.
Please take time to read these pages carefully before taking any action and convey the message to those around you. The handling protocols are presented on a case-by-case basis. Start planning your release strategy, actions needed to be taken collectively on board. Make sure that each crew member understands their role in the operation.