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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-
3
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
1994).

Cetaceans of the Mediterranean and Black Seas – 9.11