Tuna caught in the Mediterranean - Tomer Appelbaum
A large tuna caught in the Mediterranean in 2009. If immediate action isn’t taken, scientists predict some shark species in the sea will become extinct. Photo by Tomer Appelbaum
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The fish population of the Mediterranean is dwindling - especially large fish like the shark and bluefin tuna, according to a comprehensive study on Mediterranean fish published this week by the International Union of Conservation of Nature.

Prof. Menachem Green of Tel Aviv University and the other scientists behind the report, who gathered data on 519 species of fish in the Mediterranean, estimate that roughly 10 percent face the threat of extinction. Under particular threat are sharks and another related group of fish called batoids (rays and skates, which are flat, shark-like fish that live on the sea floor ).

Forty percent of the 76 species of these fish are endangered, according to the study. If immediate action is not taken, the scientists predict that in the near future, some of the shark species in the Mediterranean, which play a key role in the marine food chain, will have already become extinct.

One of the most disturbing findings of the report, according to the scientists, is the lack of information pertaining to about one-third of the fish species in the Mediterranean, many of which are in possible danger of extinction.

Among the main factors threatening Mediterranean sea life are the methods of fishing typically practiced, including the use of huge trawling nets that sweep up everything on the sea floor and often trap fish of no commercial value.

Other factors include pollution and the deliberate destruction of habitats by construction workers in shore areas. Some of these habitats serve as breeding grounds from fish.

In the eastern Mediterranean Sea, the area close to Israel, another threat has emerged from invasive species of animals that have come in from the Red Sea via the Suez Canal. These species, among them the jellyfish, feed in part on minnows and fish eggs, and in doing so, hurt the capacity for renewal.

The fish in greatest danger of extinction in the Mediterranean is the common goby, whose population is estimated to have dwindled by 80 percent during the past decade.

This is a fish often caught accidentally in fishermen's nets.

Some scientists think this species has also been affected by the rising temperature of the Mediterranean Sea, which has been attributed to global climate change.

The bluefin tuna is also in danger of extinction. Fishermen customarily surround large schools of tuna with nets and trap the fish in large quantities, in some cases jeopardizing their ability to renew themselves.

Also in danger is one of the most unusual fish of the Mediterranean, the dusky grouper - a fish that has gained fame thanks to its ability to change its sex from female to male.

It lives near rocks and is especially vulnerable to fishing activity.

The scientists who wrote the report recommend a number of measures to prevent the continued extinction of the fish.

They propose, inter alia, using different methods of fishing, limiting the use of some kinds of nets in certain areas of the Mediterranean Sea and modifying the nets to prevent certain types of fish from being trapped in them. Another recommendation is to establish areas where fishing is totally banned.