Some fisheries directly target sharks as their intended catch, but other fisheries accidentally capture sharks as “bycatch”, a term used for unintended catch. These include White, Brown Cat, Tope, Bluntnose Sixgill, Blue, Basking, Porbeagle, Spiny dogfish, Shortfin Mako, and Spotted Spiny Dogfish. In Canada there are ten species of sharks designated at risk by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). The remaining species are ignored or seen as low priorities despite their vulnerability to overfishing and their important role in their ecosystems. Sharks now represent the largest group of threatened marine species on the International Union for Conservation of Nature’s (IUCN) Red List of threatened species, yet only three of the 350 shark species (Basking, Whale and White), are protected from the pressures of international trade. Fishing has reduced many large predatory shark populations worldwide by 90% over the past century. The unfortunate reality of course is that humans are the ocean’s true apex predators, killing more than 100 million sharks each year. Apex predators also influence spatial distribution of prey species through intimidation and keep them from overgrazing certain habitats. Others scavenge the sea floor to feed on dead carcasses.
By switching to more abundant prey, they allow low populations to rebound and prevent abundant species from monopolizing a limited resource. Most sharks have diverse diets and switch prey species when certain populations are low. As apex predators, sharks feed on animals below them in the food web, and help regulate and maintain the balance of marine ecosystems. Canada’s three oceans, Atlantic, Pacific and Arctic, are home to 41 species of sharks including the Shortfin Mako, Greenland, Sleeper, Basking, Smooth Hammerhead, and even the Great white shark! Sharks often fill the role of “apex” or top predators in their ecosystems because of their large size and few natural predators.
0 kommentar(er)
