Large shark populations fall 97% in the Mediterranean
June 12, 2008

Populations of some shark species in the Mediterranean have plunged by more than 97 percent over the past 200 years, report researchers writing in the journal Conservation Biology. Several species are at risk of extinction.

The study is based on records of abundance as determined by "catch weight" of five species of sharks. While there are 47 species of shark recorded in the Mediterranean the researchers only had enough information to assess the status the five species. They suspect that other 15 species of large predatory shark have also suffered steep declines due to direct exploitation, unintended capture in open ocean fisheries, and human population pressure in coastal areas.

Sharks are particularly vulnerable to overfishing due to low reproductive rates. The new study confirmed this, showing that the size and weight of sharks decline over time. The researchers say this trend suggests that mature sharks are increasingly scarce in the Mediterranean.

Francesco Ferretti and his colleagues expressed concern that declining shark populations may have implications for the Mediterranean marine ecosystem.

White Shark caught by John G. Casey off Montauk, NY on Oct. 8, 1964. Image courtesy of NOAA.
"The loss of top predators such as sharks in other sectors of the Atlantic has resulted in changes to the ecosystem," said Ferretti, a doctoral student in marine biology at Dalhousie University in Nova Scotia, Canada. "These changes are unpredictable and poorly understood but given the decline in Mediterranean shark numbers, there is cause to be seriously concerned about the effects this could have."

"We understand too little about the consequences of losing top predators to take shark declines so lightly." said Margaret Bowman, director of the Lenfest Ocean Program, the private organization that funded the study.

Research published last year linked overfishing of large predatory shark species along the Atlantic Coast of the United States to a decline in commercially important shellfish. The authors — which also included biologists from Dalhousie University — found that population declines in bull, great white, dusky, and hammerhead sharks due to overfishing has led to a boom in ray, skate, and small shark prey species. These smaller species are key shellfish predators.

Ferretti and his colleagues say there are presently no catch limits for commercially-fished shark species in the Mediterranean Sea. Further "a comprehensive monitoring program for fisheries has been difficult to implement in the Mediterranean because of the artisanal (small and localized) nature of its fisheries and the large number of countries bordering the sea."

Worldwide, 26 million to 73 million sharks are killed each year for their fins estimated a 2006 study published in Ecology Letters. Shark fin is a popular delicacy in Asia -- especially China, where it is typically served in shark fin soup weddings, business dinners, and other celebrations, and may fetch up to $120 per bowl. Fins are usually sliced off as the shark while it is still alive.

CITATION: (June 12, 2008).

Large shark populations fall 97% in the Mediterranean.