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the target species has occasionally been studied;  fish” (Pauly et al.  1998a). According to Pauly  et
               indirect effects have been largely neglected  al. (1998a), this leads at first to increasing
               (Smith  1995).  Complex ecosystem dynamics  catches, then to a phase of transition associated
               and/or lack of research may hide cause-effect  with stagnating or declining catches.
               links, thus leaving room for continued overex-    A striking intensification of world fisheries
               ploitation. However, the unwise management of  has been recorded since 1950, which corre-
               resources has impacted the marine environment  sponded to an increase in the proportion of re-
               to the point that, today, everybody acknowledges  sources subject to declines in productivity (FAO
               the need for preservation of the remaining stocks  1997a). Recent reviews confirm that, worldwide,
               (Kemp 1996).                                   an estimated 44% of the major fish stocks are
                                                              fully exploited and are, therefore, producing
               Fishery trends and the depletion of fish stocks,   catches that have reached their maximum limit.
               worldwide.  Global totals of the amount of fish  About 16% of fish stocks are overfished, and
               caught during the past half-century provide a  there is an increasing likelihood that catches
               misleadingly reassuring view of the state of the  might decrease if remedial action is not under-
               world’s fisheries (Pauly et al. 2000).  Most scien-  taken to reduce or suppress overfishing.  Another
               tists now agree that the overall increase in the  6% appear to be depleted, and only 3% seem to
               world fishery production should not be misunder-  be recovering slowly (FAO 1998).  A global pro-
               stood for a healthy status of the marine resources.  duction model showed that the demersal high-
               The growth rate of the landings has actually de-  value species were overfished and that a reduc-
               clined steadily since 1950, and reached a plateau   tion of at least 30% of fishing effort was required
               at the beginning of the 1990’s (FAO    1994,  to rebuild the resources. Given that few countries
               1997a, 1998).                                  have established effective control  of fishing ca-
                  It has been pointed out that “aggregate land-  pacity, around 60% of the major world fish re-
               ings from various stocks which are the subject of  sources are considered in urgent need of man-
               a fishery-complex may continue to increase de-  agement action (FAO 1994, 1997a).   Such a pic-
               spite local overfishing situations, as  long as the  ture is worsened by the fact that evaluating the
               process of increase through expansion to new ar-  impact of fishing activities on the marine envi-
               eas and resource elements overshadows the proc-  ronment is a difficult issue, as fishing trends are
               ess of decrease through overfishing” (FAO  routinely based on landing data (i.e., the catch
               1997a).  For instance, the increasing catch of  brought to the fish market).  Unfortunately, these
               small pelagic species has masked the stagnation  data are largely unreliable, as they are affected by
               or impoverishment in take of demersal fish (FAO  biases that cannot be estimated (Earle 1996).  For
               1997a, Pauly  et al.  2000), and it has been  instance, the biomass of discarded fish – that can
               stressed that “the world fish supply is increas-  account for a very high percentage of the catch  –
               ingly relying on low value species, characterised   is simply ignored.
               by large fluctuations in year-to-year productivity,   In conclusion, the available data on world
               hiding the slow but steady  degradation of the  fishery trends show that marine resources have
               demersal high value resources” (Garcia and New-  been exploited beyond reasonable limits and to
               ton 1994).                                     levels  deemed unsustainable in most areas (Earle
                  Despite increased fishing effort, landings of  1996, Kemp  1996, Caddy  et al.  1998, Christen-
               some of the most important demersal fish (in-  sen and Pauly  1998, Pauly  et al.  1998a, Pauly  et
               cluding    Gadus    sp.,   Merluccius    sp.,  al.  2000).  In a recent article on Science -  co-
               Melanogrammus  sp.) decreased from 5 million  authored by 19 scientists -  it was concluded that
               tonnes in 1970 to 1.6 million tonnes in 1993,  “ecological extinction caused by overfishing pre-
               forcing the fishing industry to target other pelagic
               species on a lower trophic level, such as Trachu-
               rus capensis and  Engraulis encrasicholus  (FAO   2  A global assessment of fisheries bycatch and discards accounted
               1994).  At a global level, the phenomenon has  for 33% (range 22-47%) of the total landings (Alverson et al. 1994),
                                                              and it has been pointed out that the sum of fishery-related mortali-
               been described as “fishing down marine food    ties occurring as a result of harvesting often involves a significant
               webs”, which refers to “a gradual transition in  number of fish in addition to catch and discard, fishing mortality
               landings from long-lived, high trophic level, pis-  being the aggregate of all catch mortalities including discard, illegal
                                                              fishing and misreporting (Alverson and Hughes 1996). For accounts
               civorous bottom fish toward short-lived, low tro-  of bycatch rates and discards in Mediterranean trawling fisheries see
               phic level invertebrates and planktivorous pelagic   for instance Carbonell  et al.  (1998), Stergiou  et al. (1998),
                                                              Vassilopoulou and Papaconstantinou (1998).

                                    Cetaceans of the Mediterranean and Black Seas   –   9.10
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