An invasion of fish species into the eastern Mediterranean Sea has brought about dramatic changes in the fishing industry and threatens local species, new Israeli research indicates.
The scope of the fish invasion is the broadest in the world, according to the researchers' study of fish caught off the Israeli coast two decades ago in comparison to the types caught today.
The study, published last month in the American journal Diversity and Distribution, the study was conducted by Dor Edelist of the University of Haifa, together with Dr. Gil Rilov of the Israel Oceanographic and Limnological Research Center and Dr. Daniel Golani of the Hebrew University of Jerusalem. Dr. James Carlton, an American scientist specializing in invasive species, was also involved in the Haifa University research.
The study was designed to assess changes in the Mediterranean's fish population due to the ongoing introduction of foreign species from the Indian Ocean and the Red Sea reaching the sea via the Suez Canal. Researchers made several trips in trawlers and examined the catches in 2008-11 and compared their findings data available on catches in 1990-1994.
The findings show that within two decades there had been a dramatic change in the makeup of the catches, particularly at depths between 15-100 meters. If two decades ago the invasive species comprised 29 percent of the catch, now they make up more than half. If 20 years ago these species made up only a quarter of the biomass (the living creatures in a given area), they have now reached 55%.
The researchers note that 55 Indo-Pacific species that arrived via the Suez Canal have established themselves in the Mediterranean, the highest invasion rate of any marine ecosystem. Half of the “foreigners” were introduced during the past decade and of these, six have multiplied so rapidly that they are among the most common species now found in the eastern Mediterranean.
This extensive invasion, the researchers point out, is not only evident near the coasts and bays of the Eastern Mediterranean, but also in the open sea. The scientists noted a clear invasive trend of other species, not just fish, in the Mediterranean.
From a commercial standpoint, this extensive invasion somewhat compensates for the ongoing depletion of the local fish population due to overfishing. At the same time, the invaders are a factor in the depletion of local species with which they compete for food and breeding sites, often forcing the indigenous species out of their natural habitat.
As an example of these ecological changes, Edelist cites the Mediterranean species local fishermen refer to as jarvida (the common pandora, a type of sea bream).
“This species was very common, but in recent years it has dropped as a percentage of the catch by two-thirds,” said Edelist. “By contrast, there has been a substantial increase in the quantities of a fish called barbon (a kind of red mullet fish) which originates in the Indian Ocean. We believe that the growth of this specie is coming at the expense of the jarvida. You have to remember that invasive species are used to tougher competition in the seas from which they came, and their survival capability is higher.”
Edelist notes that these invasions are irreversible, but it isn’t clear that they are solely negative. “There are changes and we have to accept them and not be afraid of them,” he said.
Still, he and the other researchers believe that steps must be taken to reduce the rooting out of indigenous species. One of their recommendations is to limit the fishing of these species to give them a change to multiply and improve their chances of competing against the ongoing invaders.
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