What is a stranding?

Bycaught stranded Bottlenose dolphin

A marine mammal is said to be stranded when it is found on the shore, dead or alive, but unable to return to its natural habitat by its own means (weakened, injured, pathological, etc.).
There are three types of strandings:
• Individual strandings, which concern isolated individual;
• multiple strandings, which concern a large number of individuals, which may belong to several species, found stranded over a short period of time (a few days to a few weeks) and located in a restricted geographical area;
• mass stranding, which is a simultaneous stranding of several cetaceans belonging to the same species. It mainly concerns gregarious odontocete species.

What are the main causes?
The causes of strandings are multiple, but three main categories can be distinguished:
• Natural causes: diseases, predation, inter or intra specific competitions, etc.
• Anthropogenic causes: accidental capture in fishing gears, which is the primary cause of strandings in many regions of the world, collisions with vessels, noise or chemical pollution, ingestion of plastics, etc.
• Environmental causes: climate change, storms, algal toxins, earthquakes, etc.

The significance of stranding monitoring for species conservation

Common dolphin stomach content that will be used to study its diet

Marine mammal strandings are the main source of data and biological material to study these species and are an essential support to scientific research and public conservation policies. The data and samples collected allow to reinforce knowledge on the biology and ecology of the species, but also on the threats. For example, genetic analysis can be made from skin samples, age structure can be determined through to teeth analyses, feeding ecology by studying stomach contents, the state of health and the causes of mortality from marks of bycatch, evidence of diseases from the examination of internal organs, presence of contaminants in the samples collected.

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You want to develop a stranding network in your territory or strengthen it? You will find bellow:
 Some recommendations and good practices guides
 An online training