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that fish may be far more important predators of  needs, inherent complexity and dynamism of
               other fish than are marine mammals (Trites 1997,  natural systems, and inadequacy of knowledge
               Trites  et al.  1997, Mangel and Hofman  1999,  about functional relationships (Mangel and Hof-
               Trites et al. 1999).  The ultimate effect of remov-  man  1999, Reeves et al., In press).  As stressed
               ing natural top predators would be a loss  of di-  by Okey and Pauly (1999) “just as real-world
               versity, physical complexity, productivity and re-  food webs contain complex interactions among
               silience (Naeem et al. 1994, Trites 1997).     species, so too must scientists and others interact
                  The understanding of predator-prey interac-  to describe food webs in realistic ways”.  In the
               tions and ecosystem functioning therefore repre-  capacity to interact and collaborate in ways that
               sents an essential conservation means, which may  are both multidisciplinary and inspired by a genu-
               allow to evaluate  the potential effects of food-  ine search for truth reside the chances of success
               web interactions between marine mammals and    of this “ecosystem approach”.  If  given proper
               man (Mohn and Bowen   1996, Estes et al.  1998,  development and implementation, software tools
               Pauly et al. 1998b, Croxall et al. 1999).  Ecosys-  such as “Ecopath-Ecosim” (Christensen and
               tem modelling has been proposed in recent years   Pauly  1992) may greatly benefit future large-
               as a viable tool for understanding the complex  scale management.
               ecological interactions between cetaceans, fisher-  Today, the lack of comprehensive and reliable
               ies and other ecosystem components (e.g., Smith  fish stock assessments and longitudinal studies
               1995, Earle 1996).  As reported by Reeves et al.,  aimed at describing and quantifying Mediterra-
               (2001), “modelling might elucidate counter-    nean ecosystem components remains one of the
               intuitive trends which in turn could help explain  main problems to be addressed by scientists and
               why  dolphin depredations occur in some areas  managers willing to adopt an ecosystem ap-
               and not in others”.                            proach.  As long as this situation doesn’t change
                  For instance, a combination of burgeoning  “dolphins may often serve as scapegoats for un-
               fisheries, increased ocean temperature and deple-  sustainable fishing practices” (Reeves  et al.
               tion of marine mammals have been reportedly    2001).
               triggering the collapse of the kelp forest ecosys-
               tem in western Alaska (Estes et al.  1998).  A  Impact of reduced prey availability on cetace-
               chain of ecological interactions beginning with  ans
               reduced or altered fish stocks in the oceanic envi-
               ronment sent pinniped populations to decline;  Over the last decade, the reduction of food prey
               pinniped numbers became so reduced that some   resources has been considered by several authors
               of the killer whales who once fed on them ex-  as a threat of primary importance that may have
               panded their diet to include sea otters (Enhydra  contributed to the decline of some cetacean popu-
               lutris); this shift in killer whale foraging behav-  lations in the Mediterranean (Perrin 1988, Reeves
               iour prompted the collapse of the sea otter popu-  and Leatherwood  1994, UNEP/IUCN   1994,
               lation, which caused a sea urchin population  Reeves et al., In press).  It is therefore surprising
               overgrowth; unregulated urchin populations in-  that the issue has been given so little considera-
               creased rapidly and overgrazed the kelp forests,  tion.
               thus setting into motion a host of effects in the  As noted in the previous paragraph, one of the
               coastal ecosystem.  This chain of interactions was   reasons that may have discouraged research in
               probably initiated by anthropogenic changes in  this field is that ecosystem dynamics are exceed-
               the offshore oceanic ecosystem (Estes  et al.  ingly complex, and their investigation requires
               1998).  This remarkable study highlights a num-  sophisticated tools, extensive background infor-
               ber of key points about the way ecosystems work,   mation, and a multidisciplinary approach.  Whilst
               including the unappreciated importance that un-  powerful software tools and analytical ap-
               common or transient species of top carnivores  proaches have become available in the last sev-
               can have in controlling community structure, and  eral years, research is hampered largely because
               the need for large-scale approaches to  ecological  1) appropriate datasets are rarely obtainable, 2)
               research.                                      expertise in this field is still lacking, and 3) col-
                  Although the idea of multi-species or ecosys-  laboration among scientists from different disci-
               tem management may be appealing, it has been   plines (e.g., fishery scientists, fish biologists, ma-
               argued that this level of management is extremely  rine mammalogists, oceanographers etc.) is not
               difficult to conceive and implement due to data  the rule in Mediterranean countries.  Perhaps for

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