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cedes all other pervasive human disturbance to  not over-exploited, with a general trend towards
               coastal ecosystems, including pollution, degrada-  smaller individual sizes (Stanners and Bourdeau
               tion of water quality, and anthropogenic climate  1995, EEA/UNEP  2000). Small pelagic fish
               change” and that the “historical abundances of  stocks remain highly variable in abundance, de-
               large consumer species were fantastically large in  pending  on  environmental    conditions
               comparison with recent observations” (Jackson et  (EEA/UNEP 2000).
               al. 2001).                                     The effect of this kind of systematic impoverish-
                                                              ment of marine food prey resources on cetacean
               Fishery trends and the state of Mediterranean   populations is largely unknown (see “Impact of
               fish stocks. Trends similar to those observed at a  reduced prey availability on cetaceans”).
               global scale can be observed in the Mediterra-
               nean, where fisheries resources are in a state of  Competition for resources.  Human fisheries
               over-exploitation driven by rising prices and de-  have the potential to reduce prey availability and
               mand in the past decades.  Overfishing and fish-  affect cetacean food resources (Dayton  et al.
               ing practices largely account for the impact on  1995).  Such competitive interactions may be
               natural stocks and habitats (EEA/UNEP  2000).  both direct, when target prey for cetaceans and
               According to FAO, the Mediterranean fish stocks  fishermen overlap, and indirect, through the hu-
               have been “fully exploited”, with fisheries oper-  man exploitation of resources that may influence
               ating at or close to an optimal yield level, and no  the availability of cetacean food prey ("food web
               expected room for further expansion.           competition"; Earle  1996, Trites et al.  1997).  A
                  Although Mediterranean fisheries statistics are   case of possible competition between fisheries
               scarce and unreliable (Stanners and Bourdeau  and marine mammals has been studied in the Pa-
               1995, Earle  1996, FAO  1997a), and there is an  cific Ocean, where it has been suggested that the
               acute lack of general and historical data (Briand  excessive growth and capitalisation of fishing
               2000), evidence exists that overfishing and un-  fleets inevitably result in over-exploitation of the
               sustainable harvesting has led to the decline of  available resources, thus representing a threat to
               many fish stocks 3  (Caddy and Griffiths  1990, De   marine mammals.  The availability of resources
               Walle et al.  1993, Stanners and Bourdeau  1995,  that are important to marine mammals would
               FAO 1998, Briand  2000). One of the most perva-  therefore decrease with an increased exploitation
               sive ecological consequences may be the “fishing  of fish stocks for human consumption (Trites et
               down marine food webs” phenomenon (Pauly,  et  al. 1997).
               al. 1998a), and it has been recently demonstrated   Cetaceans, in turn, can rely on resources of
               that the mean trophic level of Mediterranean  economic interest and may affect fisheries
               catches has  declined significantly and quite  through direct and “food-web” competition
               steadily since the late 1950s, although fishery  (Earle  1996).  The claim that cetaceans compete
               landings increased (e.g., Pauly and Palomares  with fisheries has been used to support economic
               2000, Stergiou and Koulouris  2000). The declin-  incentives for commercial hunting, and it was ob-
               ing or flattening catch trends in Mediterranean  served that recent initiatives to quantify the im-
               areas are consistent with the observation that  pacts of cetaceans on world fisheries have been
               these areas have the highest incidence of fully-  intended to help build a case in favour of ex-
               exploited fish stocks and of stocks that are either   panded commercial whaling (Reeves  et al., In
               overexploited, depleted, or recovering after hav-  press).  However, whilst the deleterious impact of
               ing been depleted (FAO 1997a, 1998). The Euro-  overfishing on several marine ecosystems has
               pean Environment Agency also reported that un-  been well documented, it is still unclear whether
               sustainable harvesting of Mediterranean fish  cetacean removal – including the intentional kill-
               stocks has led to the decline of many, and that  ing of cetaceans charged of net depredation  -
               demersal fish stocks are usually fully exploited, if  would eventually benefit the fisheries.
                                                                 Output obtained from ecosystem models (e.g.,
                                                                  Christensen and Pauly  1992) and long-term ob-
                  Decreasing catches due to overfishing have been recorded in   servations (e.g. Estes et al.  1998) suggested that
               several Mediterranean subareas, particularly as far as demersal fish   removing natural predators from an ecosystem
               are concerned (e.g., Jardas  1985, Papaconstantinou  et al.  1985a,
               Azzali and Luna  1988, Levi and Andreoli  1989, Bombace  1990,   may have unpredictable effects, i.e. not those that
               Andreoli  et al.  1995, Jardas et al.  1997, Stergiou  et al.  1997,   could be expected based on simplistic predator-
               Ardizzone et al. 1994, Cau et al. 1994, De Ranieri et al. 1994, Levi   prey models.  The available data actually indicate

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