Study Shows Alarming Decline In Shark Numbers Around The World
Over the last 70 years, sharks have experienced considerable declines, with many species becoming threatened and endangered. Despite conservation efforts, many populations are still at risk because of overfishing and habitat loss.
Continued improvements are needed in many parts of the world to slow and reverse declines, including sharks that use coral reefs, according to a study by an international team of researchers that includes a Texas A&M University at Galveston professor.
In a comprehensive study, the team deployed more than 15,000 baited remote underwater video stations on 371 coral reefs in 58 countries . Surprisingly, results showed that no sharks were detected in almost 20 percent of locations surveyed, and were almost completely absent from coral reefs in several nations.
The study supports the belief that demand for shark products, such as fins and meat, and bycatch (sharks found in nets by fishermen seeking other types of fish) strongly contribute to the widespread declines in shark numbers around the world.
“The study globally assessed sharks at coral reefs, which included 59 different species in the Atlantic, Pacific and Indian Oceans,” Matich said. “These ranged from Caribbean reef sharks and bull sharks to hammerheads, tiger sharks and many other species, including those not tied to coral reefs.
“But sharks were completely or nearly absent from some countries, which was not expected considering the importance sharks play in maintaining the stability of marine food webs. Many of the nations that lacked sharks were characterized by low socioeconomic status, which can affect conservation and management due to available resources, including finances, personnel, food security, education and infrastructure.”
No sharks were detected on any of the reefs in six nations: the Dominican Republic, the French West Indies, Kenya, Vietnam, the Windward Dutch Antilles and Qatar. Among these, a total of only three sharks were observed over more than 800 survey hours.
Matich said the study shows if corrective steps are not taken in regions where management is still ineffective, continued depletion is highly likely, particularly for sharks that are characterized by slow growth rates, late age at maturity and low reproductive output.
Matich said that shark numbers are important because they can be a barometer of overall ocean health and ecosystem vitality.
“Sharks have important roles in marine ecosystems, but disturbance can alter this role,” he said. “A major disturbance to sharks and their ecological roles is habitat deterioration – as habitats are damaged, the resources they provide, like food and shelter, can change, often negatively. In turn, changes in shark populations can further affect the health of ecosystems because they help regulate prey populations by eating and scaring them, affecting behavior and abundance when present.”
Coral reefs are also in decline in many parts of the world, adding to the problem, the researchers concluded.
The study noted that some countries – especially the Bahamas – are combating the problem by providing sanctuaries for sharks where fishing and harvesting is prohibited. The study shows these measures are protecting sharks that use coral reefs, with the Bahamas supporting some of the healthiest populations across the world.
“Change takes time, and like many other management and conservation issues that we currently face, it’s unclear if the number of nations without sharks inhabiting their coral reefs will increase, decrease, or remain stable,” Matich said. “I’m personally optimistic based on my interactions with communities and the value they place on live sharks over dead sharks, but there is still a lot of change that needs to happen.”
The study was funded by the Paul G. Allen Family Foundation.