Changes in the catch composition of artisanal fisheries attributable to dolphin depredation in a Mediterranean marine reserve

Abstract

. Changes in the catch composition of artisanal fisheries attributable to dolphin depredation in a Mediterranean marine reserve. -ICES Journal of Marine Science, 66: 699-707.There is increasing evidence from previous studies, and from fishers' observations, that coastal dolphins use fishing nets as an easily accessible feeding source, damaging or depredating fish caught in the nets. This study investigates the impact of dolphin depredation on artisanal trammelnets by analysing the catch composition of 614 artisanal fishing operations in the Bonifacio Strait Natural Reserve (France). Common bottlenose dolphins (Tursiops truncatus) attacked, on average, 12.4% of the nets and damaged 8.3% of the catch. However, attacked nets were characterized by statistically significantly higher catch per unit effort than unattacked ones. Catch composition also differed significantly after dolphin attacks; bentho-pelagic fish were more represented and reef-associated fish less represented. Our results suggest that (i) dolphins are attracted by high fish densities in the fishing area and/or nets, and (ii) their attacks induce specific fish-avoidance behaviour, according to the fish position in the water column. Although dolphins depredate a small part of the catch, damage to nets, not yet assessed in this area, could weaken the benefits that reserves can provide to artisanal fisheries.

To ping or not to ping: the use of active acoustic devices in mitigating interactions between small cetaceans and gillnet fisheries

“…It is striking that reported depredation of gillnets by cetaceans almost always involves bottlenose dolphins; many of these reports arise from the Mediterranean (Lauriano et al 2004, López 2006, Brotons et al 2008a, Rocklin et al 2009). Several studies have addressed whether pingers reduce damage to gillnets and captured fish, testing a number of different pinger types (Table 4).…”

Interaction between bottlenose dolphin (Tursiops truncatus) and trammel nets in the Archipelago de La Maddalena, Italy

“…Fish are among the most important natural resources of the world, but because of technical improvements in catching power and development of trade, fisheries have reached an unprecedented level of exploitation (Jackson et al, 2001;Ormerod, 2003;Rocklin et al, 2009). The increasing trend in the percentage of overexploited, depleted and recovering marine fish stocks reduces the amount of prey available for natural predators (Bearzi, 2002).…”

“…Recently, in the context of declining fish stocks, the fishing industry has increasingly viewed these interactions as a problem, particularly so for small-scale fisheries (Lauriano et al, 2004;Díaz-López, 2006, 2009Rocklin et al, 2009).…”

Fish Behaviour, Learning, Aquaculture and Fisheries

“…At present we have little evidence that fishes avoid heavily fished areas, because they lack relevant stimuli for avoidance. Naïve brown trout (S. trutta, Salmonidae) avoided a section of a river where other individuals had been hooked the previous day (Young & Hayes 2004), and attraction of dolphins to a fishing area induced different avoidance reactions in different species of fishes (Rocklin et al 2009). Chemosensory cues are generally more reliable than visual cues in this context (see Chapter 4), and chemical stimuli from fishing gear could provide information about the local predation (fishing) risk.…”