Sharks: The Animal Answer Guide

10 Human Problems (from a shark’s viewpoint)

185 Chapter 10 Human Problems (from a shark’s viewpoint) Are any sharks endangered? The recognized worldwide authority on extinction risk in plants and animals is the International Union for the Conservation of Nature (IUCN), a United Nations–sanctioned clearinghouse for such information. The IUCN publishes a Red List of endangered plants and animals that it updates regularly. In 2012, the IUCN had assessed the status of 1,090 chondrichthyan species; population information was available for only half of these. When population trends indicate a species is threatened with extinction , the IUCN assigns ranks of “critically endangered,” “endangered,” or “vulnerable.” The 2012 assessments indicated that 3% of sharks, skates, and rays were critically endangered, 4% were endangered, and 11% were vulnerable. This means that 18%, or about one-fifth of assessed species, are theoretically threatened with global extinction. Whether we can assume that unassessed species are equally at risk is an unknown. That is the global view. At more local, regional levels, the picture can be even bleaker. Diver surveys at numerous Caribbean locales found few sharks other than Nurse Sharks. This conclusion stands in stark contrast to historical accounts of shark abundance in which researchers stated that a variety of sharks could be “expected anywhere at any time” in the west-Indian Caribbean. Today, except for Nurse Sharks, sharks are expected “anytime almost nowhere.” In the Mediterranean Sea, comparisons going back to the early nineteenth century indicate significant declines in large sharks, especially hammerheads, Blues, makos, Porbeagles, and thresher sharks. Human activities that have resulted in habitat destruction and pollution have undoubtedly affected shark populations. But overexploitation appears 186 Sharks: The Animal Answer Guide to be the chief cause of decline in all these examples because it interacts with aspects of the basic biology of shark species that make them vulnerable to exploitation. Because many sharks mature slowly and produce relatively few young at long intervals, they are easily overfished and their populations are slow to recover, if at all. Add to this the tendency of individuals to cross entire oceans, during which time they are exposed to fishing in multiple countries and on the high seas. Protective measures in one country do little to protect sharks when they travel to another region where protection is nonexistent . And the open ocean is largely unregulated and even harder to patrol. Given these biological traits and circumstances, it is not surprising that commercial shark fishing has a long history of collapse. A typical shark fishery experiences initially high catches of a previously unexploited stock, followed by reduced landings despite increased effort, and eventual decline in catches to the point that it is no longer economically profitable to keep fishing. After most fishing ceases, populations are slow to recover, if they recover at all. Examples of sharks that have been overfished include Common Thresher Sharks and Pacific Angel Sharks in California; Angelsharks (Squatina squatina) in the Irish Sea; School Sharks and 12 species of deepwater squaliform dogsharks including Portuguese Dogfish off Australia ; Spiny Dogfish in the North Atlantic; Basking Sharks off Ireland and British Columbia; Bull Sharks and Largetooth Sawfish (Pristis microdon) in Lake Nicaragua; Soupfin Sharks (Galeorhinus zyopterus) off the U.S. Pacific coast; Brazilian Guitarfish (Rhinobatos horkelli) in the southwest Atlantic ; and Porbeagle Sharks off Newfoundland. Even chimaeras are subject to overfishing because, like sharks, they have a slow reproductive cycle. A fishery in New Zealand for Australian Elephant Fish collapsed in the 1980s from overfishing and has taken two decades to show signs of recovery. The Porbeagle fishery of the western North Atlantic provides a classic example, collapsing after only six years. Exploitation began in 1961, with landings averaging 4,500 metric tons (MT; 9.9 million lb) per year prior to the collapse, when catches fell to around 350 MT (772,000 lb), or 8% of initial landings. Relaxed fishing led to partial recovery of this species, but only to about 10% to 20% of the original levels. Soupfin Shark landings off California peaked at 4,000 MT (8.8 million lb) in 1939, fell to 2,300 MT (5.1 million lb) in 1941, and five years later were down to 270 MT (595,000 lb), or 7% of the peak, despite intensive effort. Thirty years afterwards, populations were still below the pre-exploitation levels of the 1930s. The history of the Basking Shark “fishery” off British Columbia is particularly sad because it involved the deliberate extirpation of a harmless giant species of no commercial value, eliminated...