With the efficiency of industrialized fishing practices, in many cases non-target species are captured in fisheries, a process known as 'bycatch'. Bycatch refers to the unintended catch of non-target species that are either retained or discarded depending on the species. When discarded, these species may be healthy, injured or dead. Bycatch of shark species occurs in most fisheries worldwide, in some cases exceeding the catch of the targeted species; however, the precise extent of bycatch is often poorly documented. Sharks caught as bycatch are generally discarded at sea, which can result in high mortality. These sharks are rarely recorded in commercial fishery landings statistics.
In Canadian Atlantic waters, bycatch and unaccounted discard mortality is the primary threat to shark species. Bycatch of sharks in Atlantic Canadian fisheries is largely unmanaged, and methods to reduce these catches are either not yet implemented or poorly documented. In addition, little is known about the distribution of sharks in Canadian waters and ways to minimize the incidence of bycatch and overall shark mortality. Decline in abundance and high discard rates have resulted in the consideration of several species (e.g. porbeagle, spiny dogfish, basking shark, blue shark, white shark, shortfin mako) for listing under Canada's Species at Risk Act.
The Northwest Atlantic longline swordfish fishery has the worst 'bycatch to target catch ratio'. Bycatch in this fishery accounts for nearly half of all the catch of swordfish by weight caught by longline vessels. Sharks - particularly blue sharks - as well as other marine species including turtles, mammals and other fish, are caught in this fishery. However, this fishery has taken steps to reduce its bycatch and mortality of non-target species through the voluntary actions (e.g. adoption of circle hooks and safe handling equipment).
Bycatch can be reduced by a combination of fishing regulations, technological changes in gear and other changes in fishing procedures. Several strategies to reduce shark bycatch have been tested around the world. Many of these have focused on gear and fishing procedure modifications. For more information on bycatch mitigation, click here.
To review fishing methods that produce bycatch, click here.