Fishing in the Mediterranean is mainly concentrated in areas where the continental shelf slightly extends into the sea, as in the Gulf of Lion. Coastal fishing in the Sanctuary accounts for about 90% of fishing vessels, with small, polyvalent boats generally used in depths of 100 m (source: IFREMER). Fishing is mainly focused on species with a high economic value, and the activity is generally limited to the 1,200 sailors in the Provence-Alpes-Côte d’Azur region and the 10,000 tons of fish they catch.

The development of new techniques and the gradual extension of fishing activities to areas further out from the coast and depths of over 800 m have allowed industrial fisheries in the Mediterranean to expand. These new deep-water stocks are still not thoroughly understood, however, and are often more vulnerable, belonging to ecosystems with low productivity levels and living in habitats with low resilience thresholds.

The negative impact of fishing on cetaceans, especially in terms of accidental catches, the deliberate removal of cetaceans from certain areas and increased pressure from fishing on the fish stocks that cetaceans feed on, has increased with the global growth of fishing activities in recent years. An accurate study on this topic has yet to be conducted within the Sanctuary, as capture rates are still not being accurately reported.

The fishing equipment that can be the cause of ‘clashes’ between fishermen and cetaceans includes:

  • Driftnets (for tuna and swordfish fishing)
  • Bottom trawling, nets (for catching demersal and benthopelagic fish)
  • Dragnets (for catching demersal, benthopelagic and pelagic fish)
  • Pelagic longline fishing (used in Japan to catch tuna) and other longline techniques (used for both large pelagic fish and demersal fish)
  • Cargo nets and seine nets (for pelagic fish) are also sometimes used

In addition, the development of aqua-farming activities in the Mediterranean increasingly impacts the cetaceans’ feeding habits, as they are often opportunistic animals.

 

Fishing with thonaille nets

In order to improve the popular understanding of thonaille fishing as it is currently practiced, and with a view to objectivity and transparency, the following information was put together by the French Part of the Pelagos Sanctuary.

Thonaille fishing is a traditional economic activity that currently involves around eighty boats, all under 18 m. It is a form of pelagic fishing that is usually carried out between May and October, six days a month and when there is a new moon, between 20 km and 100 km from the coast.

Thonaille fishing uses vertical driftnets to catch pelagic species such as tuna. The nets are between 7 and 8 m in height and between 3,700 m and 9,260 m in length. Their lower side is weighed down by a floating anchor and they are held on the surface by buoys fitted with radar reflectors and flashing lights. The nets stay on the surface, as they are more buoyant than the weights attached to them. They are always formed of a single net layer. Pingers, devices that emit an acoustic signal, are attached in order to alert cetaceans to the presence of the net and limit bycatches. According to on-board CNRS researchers, who have accompanied trips since 2000, bycatches have been reduced by around 80% with the use of these acoustic warning devices. However, this technique needs to be honed further and research into the sonar signals produced by dolphins that attack nets needs to be carried out.

Thonaille nets should not be confused with seine nets, which are used by large boats (50 m and longer). Between 60% and 70% of bluefin tuna catches involve the use of seine nets, with the remainder caught by longline fishing, rod fishing, thonaille fishing, ‘courantille’ fishing (using a type of driftnet) and trap net techniques (source: IFREMER).

 

Threats

Bycatches, incidents involving fishing nets and common bottlenose dolphins (Corsica), reduction of food stock, greenhouse gaz emission.