Thresher sharkA new scientific study has concluded that sharks in the Mediterranean Sea have declined by more than 97 percent in abundance and “catch weight” over the last 200 years.

The findings of the study published in the journal Conservation Biology, suggest several Mediterranean shark species are at risk of extinction, especially if current levels of fishing pressure continue. Study lead author Francesco Ferretti and his colleagues are concerned that the declines in sharks may have implications for the broader Mediterranean marine ecosystem.

Ferretti said: “The loss of top predators such as sharks in other sectors of the Atlantic has resulted in changes to the ecosystem. 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.”

Forty-seven species of sharks live in the Mediterranean Sea, of which 20 are considered top predators.

The study authors only had enough information to assess the status of five of the twenty large predatory shark species in the Mediterranean. Of those analysed, almost all of the large sharks have decreased in abundance because of unintended capture in open ocean fisheries, targeted shark fishing, and human population pressure in coastal areas. Sharks are especially vulnerable to overfishing and slow to recover from depletion because they generally grow slowly, mature late and produce few young.

The mean size of sharks caught in the Mediterranean is among the lowest in the world. The study reveals that size and weight declines over time indicate that more young and immature sharks are being caught.

There are currently no catch limits for commercially-fished shark species in the
Mediterranean Sea. 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.

Only five species of sharks offered sufficient information for analysis, including the blue shark, one thresher shark species, two mackerel shark species and one hammerhead shark species. The blue, smooth hammerhead and thresher sharks were classified as “Vulnerable” according to the latest IUCN-World conservation Union Red List Criteria for extinction risk. Two mackerel sharks, porbeagle and shortfin mako, were classified as “critically endangered”. Many other large sharks are classified as “Data Deficient”.

To view a summary of the Conservation Biology paper, visit:
http://www.lenfestocean.org/publications/ferretti_med_sharks.html

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