Challenges in the South Eastern Mediterranean

08 Jan 2016
Mnemiopsis leidyi. Steven G. Johnson/CC BY-SA 3.0 via Wikimedia Commons

Mnemiopsis leidyi. Steven G. Johnson/CC BY-SA 3.0 via Wikimedia Commons

A multidisciplinary scientific conference dealing with the dynamics of the Levant Basin, attended by international and Israeli experts, took place in November at the foot of Mt. Carmel, Israel. Menakhem Ben-Yami reports.

Entitled ‘Batsheva de Rothschild Seminar: Environmental Science and Policy – Challenges in the South Eastern Mediterranean’,  it was much more than a conventional seminar, due to the many different aspects of the unique, continuously-changing marine ecosystem of the Levant Basin (LB), including the waters of Turkey, Cyprus, Syria, Lebanon, Israel and Egypt, with its huge natural gas reserves. Aspects such as pollution, radioactivity, and the dramatic changes in Eastern Mediterranean fish populations were discussed.

As the organisers rightly indicated, while the Med represents only 1% of the world's oceans, it is bordered by 19 countries and, consequently, affected by their growing population, overfishing, pollution caused by discharge of industrial and municipal sewage, and agricultural and urban runoff.

Professor Barak Herut, the DG of the Israel Oceanographic and Limnological Research Institute described in an opening address the ongoing dramatic changes in the LB, the poorest and ecologically very sensitive Mediterranean ecosystem. Atlantic water enters the Med through the Gibraltar Straits and is carried eastward by the Mediterranean counter-clockwise current, while the Red Sea water is entering through the Suez Canal that, for the last 150 years, has served as a passageway for a plethora of Red Sea fish and other marine organisms carried to the Mediterranean by the Canal's northward current. The High Dam on the Nile erected in the middle of the 20th Century deprives the LB biota of nutrient-rich sediments. The Bosphorus and Dardanelles Straits enable mixing of the less saline Black Sea waters and its biota with the LB ones.

Ctenophores
WF&A heard from Dr Dror Angel of the University of Haifa, on the consequent occurrence in the LB of Mnemiopsis leidyi, a ctenophore comb jelly, a recent arrival from the Black Sea, which devastated the Black Sea fishing industry after incidental introduction in the 1980s. Only after 1999, when another ctenophore, Beroe ovata - that feeds almost exclusively on Mnemiopsis leidyi - had been introduced, the Black Sea fisheries recovered. Fortunately, in the LB both ctenophores have shown simultaneously.

Dr Angel's lecture theorised on the insistent occurrence of swarms of jellyfish in the LB. Accordingly, fish and jellyfish subsist on overlapping food resources. With the development of fisheries and the consequent reduction of the virgin fish population in the ecosystem, jellyfish enjoy a bigger food base to exploit and propagate.

Dr Shirra Freeman of the Environmental Health Unit at the Galilee Research Institute talked about the risks and benefits of local fish consumption. Fish contain such valuable components as polyunsaturated fatty acids and selenium, both nutritionally essential for humans. On the other hand, however, some species in some areas may contain methyl mercury and organic pollutants. In general, she told WF&A that, for example, the fish farmed under controlled conditions in ponds on land are much less contaminated with heavy metals, etc, than marine fish, especially the older ones like tunas and sharks, which accumulate more mercury than they are able to exude.

LB ecosystem
Dr Daniel Golani, a prominent Israel ichthyologist whose research takes him over the whole LB, presented the main fisheries-oriented lecture. He spoke to WF&A.   

WF&A: During the seminar's sessions an attempt was made to describe the LB's ecosystem using mathematical models of extraction of fish based on averaging the available prolonged time data. Would such methodology give an accurate picture of the reality?

DG: The Eastern Med, or what's called the Levant Basin, since the opening of the Suez Canal has been undergoing continual change in fish population composition, and in particular in the specific composition of the commercial ones. Initially, the changes have been rather gradual and insignificant, the noticeable exception beingthe goldband goatfish (Upeneus moluccensis) that soon afterwards managed to establish considerable populations all over the Levant Basin. More recently, the fisheries in the LB assumed unique character, owing to their multispecies and to ever changing external conditions. The immigration of Red Sea species started developing at a revolutionary pace in parallel to several environmental phenomena, increasing water temperatures being only one of them.

WF&A: Was this immigration's impact on the LB fish resources significant?

DG: There are many examples, but most typical is the expansion of Nemipterus randalli (Randall's threadfin bream), an Indian Ocean/Red Sea species, which had been still extremely rare in 2004-5, and within three-to-four years became the most important fish in trawl catches at depths between 30 and 70m. Also, Scomberomorus commerson (Narrow-band Spanish mackerel) that had been first recorded here in 1935, only in the 1980s created a considerable population; a Red Sea fish Saurida undosquamis or S.lepsessianus (Brushtooth lizardfish) was first reported in the Levant Basin in 1953 as a counterpart to the Atlantic lizardfish Synodus saurus, both equally rare. Then, between 1954 and 1956 its population exploded to partly co-exist and partly compete with Merluccius merluccius (Atlantic hake), only to approach a few years later some 30% of the total Israeli trawl landings.

WF&A: Do these dynamics continue?

DG. Well, the hake has totally disappeared from catches, probably leaving the LB to cooler waters farther west. Otherwise since 2000, only non-commercial ones are still immigrating.

WF&A: What about the claims of overfishing, especially by trawlers?

DG: The fact, which evidently doesn't fit the hyper-green allegations, is that despite all these changes in Israeli fisheries, including the explosion in the numbers of recreational fishermen within a few decades by two orders to the present 70,000, and the changes in effort and catch composition, the trawl landings remain stable, indicating that the basic stock is still healthy. This may be caused by rather low fishing mortality, and also continual influx of fish from neighbouring areas. Fish don't recognise political borders, and swim in and out without passports and visas.

WF&A: Thank you, Dr Golani.