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posing the web are degraded (Jefferson et al. expanding since 1990. Fishermen blame the fish
1992). farms for the large numbers of dolphins staying
Entanglement in discarded gear is an often in Cyprus waters throughout the year, and claim
overlooked, but potentially important problem. that the dolphins are attracted primarily by the
For instance, when proportions of litter were large shoals of fish, mainly boque (Boops boops),
studied on south-eastern Alaska beaches, 76-85% that have appeared in the vicinity of fish farms
by weight consisted of trawl-web fragments, in- (UNEP 1998b).
dicating surprisingly high quantities of nets dis- Bearzi et al. (In press) noted a relative in-
carded at sea. Net fragments of all kinds may act crease in time spent by bottlenose dolphins
as “ghost nets”, and may entrap cetaceans and around coastal fish farms in eastern Ionian
other marine life while they are simply swim- Greece after 1999, and observed that increased
ming by, or when they are trying to catch food nutrient levels, complex substrate and provision
that is entangled or in the proximity of the net. of food bait in the proximity of the cages may
Some of the fragments may have food organisms create a favourable environment and attract po-
growing on them, or entrapped by them, and may tential bottlenose dolphin food prey. In 1981-
occasionally be regarded as food by individual 2000 the aquaculture production of marine fish in
cetaceans (Fertl and Leatherwood 1997). Greece increased by 300%, largely due to the de-
Several reports exist of marine mammals en- velopment of cage technologies in inshore waters
tangled in net fragments or other discarded fish- (Anonymous 2000, EEA/UNEP 2000).
ing gear (O’Hara et al. 1986, Fertl and Leather- In north-eastern Sardinia the construction of a
wood 1997). The available data for the Mediter- floating fish farm has been linked to increased
ranean do not allow to evaluate the relative im- bottlenose dolphin abundance, and dolphin be-
portance of this threat, as compared to bycatch in havioural changes were recorded possibly as a
operating fishing gear. However, it is clear that result of high fish density around the farming
the practice of discarding nets at sea should be area (Diaz Lopez et al., In press).
prohibited, and measures should be taken to re- So far, there is no published evidence that ce-
duce the occurrence of nets and other fishing gear taceans may cause direct damage or indirect im-
abandoned or lost at sea (e.g., by active removal pact (e.g., by inducing stress in farmed fish) to
from the marine environment whenever possi- Mediterranean aquaculture facilities, but it must
ble). be considered that the possibility that coastal dol-
phins may one day learn to exploit this relatively
Entrapment in tuna traps. Traditional tuna new food source (e.g., by jumping into the cages
traps were largely used in Italy in the past, and or damaging them to gain access to the farmed
could entrap coastal cetaceans such as common fish) represents a source of concern (Bearzi et al.
bottlenose dolphins. The animals, taken alive and In press). Bottlenose dolphins are known for
rarely reported by fishermen, were usually killed their behavioural flexibility and their capacity to
together with tuna in the "death chamber". How- learn new feeding strategies (Shane et al. 1986).
ever, this fishing method is becoming increas- If dolphins ever learn ways of gaining access to
ingly rare in the Mediterranean, and the current the farmed fish, hostile reactions by fishermen
impact of these traps on cetaceans is negligible can be expected (Würsig, In press).
(Di Natale and Notarbartolo di Sciara 1994).
Competitive interactions between cetaceans
Cetacean interactions with aquaculture facili- and fisheries
ties. Interactions between dolphins and aquacul-
ture facilities in the Mediterranean appear to be During the last century, and particularly in the
occurring with increasing frequency, possibly last 50 years, overfishing practices have so im-
owing to: 1) the rapid expansion of fish farming poverished the marine environment that present
in coastal waters, and 2) opportunistic behaviour and future generations of cetaceans (and fisher-
shown by the dolphins possibly as a result of de- men) are in trouble (Pauly et al. 2000). In study-
creasing food resources (Reeves et al. 2001, ing the effects of fishing and trying to manage
Bearzi et al., In press). fisheries, man has apparently ignored changes in
In Cyprus, fishermen claim that dolphins have food web dynamics, or has not paid enough atten-
increased spectacularly as a result of the devel- tion to complex cause-effect relationships. Only
opment of aquaculture, which has been rapidly the often overwhelming direct effect of reducing

Cetaceans of the Mediterranean and Black Seas – 9.9