ECOSYSTEM EFFECTS OF FISHING IN THE MEDITERREAN: AN ANALYSIS OF THE MAJOR THREATS OF FISHING GEAR AND PRACTICES TO BIODIVERSITY AND MARINE HABITATS

Most of the major impacts of fishing on the ecosystems recorded around the world occur in the Mediterranean. They vary from local effects on the sea bottom caused by trawler gears to large-scale impacts on cetacean populations driven by driftnet bycatch. This variety – which makes the Mediterranean a unique global model for the implementation of the Ecosystem Approach to Fisheries – is due to four main interrelated factors: the huge diversity of fishing gears and practices, the very high intensity of fishing, a high diversity of habitats distributed from the shallow-waters to the deep-sea and the oceanic domain, and an important biological diversity. The latter is demonstrated by the Mediterranean presence of a vast array of vulnerable species, many of them listed in international protection agreements that include emblematic sharks, turtles, whales and seals. Mediterranean fisheries are not an exception in the context of the general declining trend shown by elasmobranch populations and their fisheries around the world. Information indicating to unsustainable catch rates of rays (including the disappearance of certain taxa from commercial catches) and other demersal species deserves special concern. The high elasmobranch bycatches – and even commercial catches – achieved in many pelagic fisheries, notably longlining and driftnetting, also appear to be a potential danger for several species. Longline fishing is also the main cause of seabird mortality in Mediterranean fisheries. Indirect effects of fishing on seabirds related to food availability, driven by discards, are particularly important. Fishing in the Mediterranean basin is clearly a major threat to marine turtle populations, which are massively bycaught. Longline fleets are a major threat in the whole region, particularly on the Loggerhead turtle population, as are trawlers and small-scale gears in particular areas, such as the Gulf of Gabes. The special vulnerability of marine turtles to high mortality rates of adults and sub-adults makes the maximization of the survival of individuals at sea a conservation priority. As for marine mammals, the information available describes a wide variety of interactions between cetacean populations and fishing fleets in the Mediterranean, involving almost every kind of major fishing gear commonly in use. However, driftnet fisheries and, to a much lesser extent, small-scale fisheries using fixed nets and purse seine fisheries appear to account for the highest impact and are also responsible for the highest rates of direct human-induced mortality. The reduced population of monk seal in the Mediterranean is also victim of both direct mortality by artisanal fishing gears and an increasing scarcity of food resources driven by overfishing. The impact of fishing on the seabed concerns mostly the use of bottom-trawling gears, namely otter trawls, beam trawls and dredges, together with some aggressive practices affecting rocky bottoms such as dynamite fishing and fishing for coral and date mussels. Trawling impacts on seagrass beds by both suspending sediments and directly damaging the vegetal mass, have the most dramatic consequences on Posidonia beds. As for particular fishing gears, bottom trawling, longlining and driftnets arise as those with most impact on marine ecosystems in the whole Mediterranean region. Evidence shows that the effects of fishing in the Mediterranean go far beyond the isolated impacts on overfished target species, vulnerable non-commercial groups or sensitive habitats. The ecosystem effects of fishing in the Mediterranean are also conspicuous at the systemic level, as highlighted by the massive ecological footprint of fishing or the marked effects on the foodweb structure. A holistic approach should therefore be adopted if the overall changes to the structure and the functioning of marine ecosystems caused by fishing are to be remedied.