Strandings of marine mammals

Since 1972 France has had a network unique in the world for documenting strandings of marine mammals: the Réseau National Échouage (RNE), the national stranding network. Run by the Observatoire PELAGIS (CNRS, Université de La Rochelle), it rests on a dense mesh of more than 500 correspondents spread along the whole of the mainland and overseas coastline. It is one of the pillars of the scientific monitoring of marine megafauna in France.

A structured organisation along the whole coastline

The RNE rests on a network of volunteers, staff from naturalist associations, employees of public bodies (OFB, DREAL, local authorities) and veterinarians. All are trained regularly in stranding response procedures, whether for carcasses or, more rarely, for live animals.

The whole arrangement is overseen by a steering committee bringing together scientists, institutional representatives and field members for each maritime seaboard. A single number allows the network to be alerted seven days a week:
05 46 44 99 10

Why study strandings?

Cetacean strandings, dramatic though they are, are rare opportunities to obtain essential biological data on species that are hard to observe at sea. Every carcass is subject to a rigorous examination protocol, including:

Toxicological analyses (heavy metals, pesticides, endocrine disruptors)
Parasitological and infectious studies (morbillivirus, brucellosis, toxoplasmosis)
Determination of age, sex, reproductive state and nutritional condition
Necropsies in an approved veterinary laboratory where the state of preservation allows

These data are crucial for understanding the pressures on cetaceans and for guiding conservation policy.

Worrying figures

Strandings are rising steadily. In 2017 the count was:

1,642 cetaceans stranded on the Atlantic seaboard, 900 of them in the first quarter alone
248 seals reported on the same coastline
78% of the strandings involved the common dolphin and the harbour porpoise
125 cetaceans in the Mediterranean, mostly striped dolphins
62 strandings reported in the overseas territories, with coverage varying widely between them

Since 2019, critical peaks have been observed, in particular on the Atlantic seaboard, where bycatch in fishing nets accounts for up to 90% of the causes of death recorded in stranded dolphins.

Distribution of cetacean strandings in France in 2017

What causes strandings?

The main causes of death observed through the RNE are:

Bycatch in trawls or set nets
Collisions with ships, in particular in the Mediterranean
Chemical pollution (heavy metals, plastics, phthalates)
Intense noise pollution (sonar, underwater explosions)
Viral epizootics (morbillivirus), sometimes devastating
Severe parasitism (Crassicauda, Anisakis)
Climate change, still poorly understood but under study

Worth noting: plastic ingestion is observed in some cases (sperm whales, ziphiids), but it is rarely fatal in mainland France.

What should you do if you find a stranded cetacean?

Acting alone is forbidden. Cetaceans are protected by law. If you come across one:

Do not move the animal or pour water over it.
Protect the blowhole (the breathing hole) if the animal is alive, without pouring water into it.
Contact the RNE immediately: 05 46 44 99 10

There are specific procedures laid down by the authorities, in particular for live animals. Apart from rare cases of refloating, euthanasia may be decided on to limit suffering.

Who can join the network?

The RNE is now well structured. Taking on new correspondents depends on local needs and on skills. Naturalist experience, veterinary knowledge or strong motivation are valued. Most new members are sponsored by an experienced correspondent before being accredited.

A tool serving science and public health

Beyond knowledge of cetacean populations, the RNE plays an important part in health surveillance. Some zoonoses (marine brucellosis, erysipeloid, vibrio) can present risks to humans. Coastal veterinarians are central to assessing these situations.

The Réseau National Échouage is therefore far more than a monitoring tool: it is an essential link between science, population management and public health. It actively helps to document the effects of human activities on marine mammals and to change practice so as to protect them better.