Sharks in the Mediterranean Sea have suffered dramatic declines in the past few decades as overfishing has taken its toll on the sleek and ancient predators. Some species, including hammerheads and threshers, have dwindled by more than 99%, according to historical fishing records examined by conservationists.
Others, including the blue shark and two species of mackerel shark, have also experienced population falls of at least 96%. Sharks are particularly vulnerable to overfishing because they grow slowly, reproduce late and produce few young. In the past they were considered pests.
In the journal Conservation Biology, a team led by Francesco Ferretti at Dalhousie University in Nova Scotia, Canada, describe how the sharks’ demise is spelled out by fisheries’ logbooks.
The records show hammerheads all but vanished from coastal waters in 1900, and have barely been spotted in the open sea for 20 years. The researchers conclude that the hammerhead population has fallen 99,99% in 200 years.
Since the mid-1950s blue sharks have declined by 96,5%, while records from long-line fisheries suggest a 99,99% fall in mackerel sharks.
The typical size of sharks caught in the Mediterranean is among the lowest in the world, indicating that more young sharks are being caught.
”The loss of top predators such as sharks in other sectors of the Atlantic has resulted in changes to the ecosystem,” said Ferretti. ”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.”
Conservation groups fear that without strict catch limits on sharks, many of the 47 species in the Mediterranean will soon become locally extinct. Margaret Bowman, director of the Lenfest Ocean Programme, which supported the survey, said: ”We understand too little about the consequences of losing top predators to take shark declines so lightly.” —