Bycatch events are a significant cause of death among cetaceans, particularly dolphins. Estimates indicate that every summer between 2000 and 2005, from 80 to 250 striped dolphins were accidentally captured in fishing nets. Findings suggest that young dolphins are more vulnerable to capture in August, while the highest number of dolphins is captured in September. The impactct of bycatches on the survival of the striped dolphins population is difficult to estimate, depending on whether the issue is addressed in terms of the local population or on the broader scale of part of the western Mediterranean Basin.

It is also worth remembering that striped dolphins are not the only species that are bycaught. Sperm whales, pilot whales, common bottlenose dolphins and Risso’s dolphins are species that are low in number and bycaught by fishing nets. These bycatch events are a major concern.


Fishing with "thonaille" nets is reputedly very selective, targeting two species that account for 96% of all those captured:

  • bluefin tuna (77%);
  • swordfish (19%);
  • the remaining 4% are species captured accidentally, mainly striped dolphins but also sperm whales, pilot whales, Risso’s dolphins and loggerhead sea turtles.

Assessing the impact of this kind of fishing on cetacean populations is not easy, however. The data are difficult to quantify and we can only make estimations regarding the real impact on cetacean populations. We thus need to make a relative comparison of the number of bycatch events for each species versus the size of the population, and also as a function of the technical means deployed for fishing trips.

Here are the results of the study conducted on bycatch events by French Part of the Sanctuary. For more information, go to and

2000 - Conducted by the Marseille Oceanographic Centre
- Estimated number of dolphins bycaught: 346 +/- 146
2004 - Conducted by GECEM
- 4 boats with observers / 25 monitoring trips between July and September
- 10 dolphins bycaught
- NB: Sample deemed non-representative, limited by the study’s delayed start
2005 - Conducted by GECEM
- 79 trips between June and September
- 8 striped dolphins bycaught, with an estimated 81 bycaught by the group of boats every year


Management options

Striped dolphins are an internationally protected species (covered by, among others, the Bern Convention and the Bonn Convention). In addition, thonaille fishing is used in the Pelagos Sanctuary, which is also a registered SPAMI, during a key feeding and reproductive period for this species.

Thonaille fishing has been the subject of active discussions between fishermen, administrations and scientists, in an effort to find a practical solution for limiting bycatches while allowing fishermen to continue their traditional activity. Thonaille fishermen themselves are concerned by bycatches and have shown a clear desire to apply techniques to limit them. Since 2000, they have participated in a scientific study developed by partners from the French Part of the Pelagos Sanctuary.

In 2002, when this fishing method was deemed by the European Union to be a form of driftnet fishing and was therefore banned, the French Ministry of Agriculture and Fishing, in conjunction with the Port-Cros National Park, which animates the French Part of the Pelagos Sanctuary, and the PACA Regional Council, sought to preserve this longstanding traditional technique, limited to a small group of fishermen. A Special Fishing Permit and accompanying Charter were thus negotiated with the fishermen. This Charter set out requirements for, among other stipulations, the use of ‘pingers’ (acoustic warning devices), authorizing observers on board, reducing the length of nets that are to be fully extended against the current, and the interruption of fishing activities in the waters covered by the Pelagos Sanctuary between August 15th and September 15th.

This decision had been made in an effort to preserve this traditional Mediterranean practice, despite the European Union’s ban on using driftnets. As a result, France was forced to stop thonaille fishing at the behest of the Council of State.

The Fishing Authority is currently awaiting a legal decision from the European Court that would allow the EU’s ban on thonaille fishing to be temporarily deferred, with the long-term aim of obtaining an exemption based on the claim that the technique does not involve the use of a real driftnet. In this case, thonaille fishermen will have to adhere to the quotas and regulations relating to tuna fishing in the Mediterranean.