06 April 2011

Dolphins vs fishers: who is right?

The following article has become available online:

Dolphins and coastal fisheries within a marine protected area: mismatch between dolphin occurrence and reported depredation

Giovanni Bearzi, Silvia Bonizzoni, Joan Gonzalvo

Aquatic Conservation: Marine and Freshwater Ecosystems (2011)
DOI: 10.1002/aqc.1179

1. Dolphins are often blamed for reducing fisheries catches and may be killed in retaliation. Depredation of fishing gear in coastal Mediterranean waters is normally caused by bottlenose dolphins. Economic impact, however, may be modest even within areas of reportedly acute conflict.
2. Boat surveys and interviews were conducted to investigate dolphin occurrence and interactions with fisheries within the 167 km2 Porto Cesareo Marine Protected Area (MPA) in southern Italy. Based on 69 interviews with fishermen using bottom-set trammel and gill nets, there was reportedly a high occurrence of depredation by bottlenose dolphins. Depredation was reported by 92% of the fishermen operating in or near the MPA, and 67% of them claimed an economic cost in excess of ?1000 per year, with a mean reported cost of 2561: a higher impact than in other Mediterranean studies.
3. According to local fishermen, dolphin occurrence and depredation peaked in spring and autumn, coincident with the study's surveys at sea. Dedicated visual surveys totalling 1255 km of effort, however, resulted in no encounters with cetaceans. Information from interviews and boat surveys was therefore contradictory, suggesting that reports of acute depredation do not imply a constant presence of dolphins within the MPA.
4. While depredation in the MPA might be caused by wide-ranging dolphins or incursions occurring overnight, damage may well be overestimated or over-reported. As local fishermen had previously benefited from subsidies, interviews made during this study could be perceived by some as an opportunity to influence future decision-making regarding monetary compensation for the impact of depredation.
5. Evidence from interviews also indicated that species and factors other than dolphins were responsible for part of the damage.

A pdf copy can be obtained from the journal's web site (subscribers only)

ITALIANO: Spesso i pescatori lamentano danni alle reti a causa dei tursiopi. Uno studio condotto nell'area marina protetta di Porto Cesareo mette a paragone le interazioni riportate con gli avvistamenti di delfini in mare da parte dei ricercatori: ne emergono delle discrepanze che fanno pensare che la predazione delle reti da pesca da parte dei tursiopi sia sovrastimata.

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