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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

Cetaceans of the Mediterranean and Black Seas – 9.12