INTERACTIONS BETWEEN CORSICAN FISHERMEN AND COMMON BOTTLENOSE DOLPHINS

Ever since humans began using nets to fish in the Mediterranean, there have been encounters between marine mammals and fishermen.

Common bottlenose dolphins, Tursiops truncatus, seem to be the species most commonly involved in such encounters. Generally sociable, they tend to favor coastal areas and often swim alongside fishermen on the narrow continental shelf – in fact, they target the same species of fish (red mullet, sea bream, phycid hake) and occasionally make use of fishing techniques – consuming fish caught in nets and entering nets to feed directly. These incidents can lead to holes being made in the nets.

As part of 2000’s Tursiops Campaign, which was part of WWF France’s Cap Ligure program, it was noted that there had been clashes between fishermen and common bottlenose dolphins in Corsica. Different environmental protection groups (associations, administrative authorities for protected areas, institutions) decided to implement the Life LINDA program with a view to reducing interactions between common bottlenose dolphins and human activities.

In an attempt to offer a satisfactory response to the building conflict between the Corsican fishing community and common bottlenose dolphins, a protected species, the Life LINDA tackled the issue in several stages:

1. Objectively assessing the scale of these interactions
2. Examining the impact of these interactions on fishing profits, in terms of repairing nets, making new nets and resource depredation
3. Setting out alternative practices to limit these interactions

The results of these scientific studies, conducted as part of the Life LINDA program, showed that:

• On average, 11% of Corsican fishing nets were attacked, with an average of one trip in five being subject to an encounter. Nets were damaged as a result of these attacks. These encounters between fishing nets and common bottlenose dolphins were representative, requiring additional research to assess the impact of net attacks
• There was a significant increase in CPUE (‘catch per unit effort’) when there were direct attacks, as well as when dolphins were present in the area. Two explanations for this phenomenon were proposed. First, common bottlenose dolphin might actively lead fish into the fishing nets with a view to consuming them after doing so. Second, it is possible that the fishermen and dolphins both go to the areas where there are the most fish and where fishing proves more productive.
• By taking fish from the nets, common bottlenose dolphins also damage these nets (generally making a ‘tongue’-shaped hole in them), making them difficult to repair. In the course of one 180-day fishing season, nets were attacked on an average of 35 days, amounting to two nets being lost.

In any case, these interactions caused a financial loss to the fishermen due to holes in the nets and to fish not being sold as a result of having been partially eaten by dolphins.

It was thus necessary to find a compromise between protecting common bottlenose dolphins and ensuring acceptable working conditions for fishermen, especially since the species is the focus of national and international Agreements and because it faces other threats, such as accidental catches in nets and overfishing.

MANAGEMENT OPTIONS

The Life LINDA program, which came to an end in 2007 after three-and-a-half years, found that although no single all-encompassing strategy could be used, the tests conducted showed that certain changes in technique could be used to significantly limit interactions. Three alternative fishing strategies for limiting encounters were chosen based on tests and on the assessment of the financial cost of adopting this new approach:

• Using nets of 5 mm mesh size rather than 7 mm or 9 mm. The smallest mesh size, for which the CPUE is half that of the 9 mm mesh size, offers the same financial return as it favors the capture of more commercially valuable fish. There are many advantages attached to this option: it reduces the number of attacks; 75 % of catches are fish of high commercial value and essentially adults, and the nets are easier to untangle. However, it is important to preserve a range of fishing practices, and not limit these to the single technique of the 5mm mesh size trammel nets or to the extended use of longlines, which could lead to the imbalance of catches at the expense of larger carnivores.
• Reducing the time nets are left in the water (twelve hours rather than twenty-four), is only possible if there are a range of fishing sites nearer the home port, which is not always the case.
• Using longline fishing. This technique is very profitable and is the best avoidance strategy, with a 0% interaction rate over a sample three-year period and a CPUE of large individuals that does not affect juvenile stocks. However, costs for the purchase new equipment are unavoidable (although quickly amortized) and of particular note is the fact that the working day would be extended by between 2 and 3 hours, as the use of the technique requires practice and also good weather conditions.

The development of ‘Pesca tourism’ or ‘fishing tourism’ could also provide a solution to the fishermen’s problem of attacks to their nets by common bottlenose dolphins. The practice combines a number of activities, bringing fishing and tourism together as well as the presence of whale watchers on board the boat. Dolphins would then cease to be competitors and would instead become an asset in the development of ‘Pesca tourism’.

This three-and-a-half-year program showed that by working with professionals of the sea, it is possible to find sustainable solutions to satisfy everyone.