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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
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