Why study strandings?

Cetacean strandings offer a unique scientific opportunity to understand the biology, the health and the ecological interactions of these marine species. They are a valuable source of information, irreplaceable, and largely underestimated in the monitoring of marine ecosystems.

A unique window on the biology of marine mammals

Unlike invasive methods at sea, strandings give access to the whole animal: internal organs, tissues, baleen, teeth, stomach contents. They therefore make it possible:

To determine age (from the teeth or the baleen).
To assess reproductive status (gestation, lactation, sexual maturity).
To measure growth and biometrics precisely.
To analyse population genetics at the scale of several basins.

Digestive contents and stable isotopes reveal diets, feeding areas and migratory movements.

Continuous health surveillance of populations

Strandings constitute a natural epidemiological surveillance system. Necropsies make it possible to identify the causes of death: pathogens, bycatch, collisions, poisoning.

Viral epizootics (morbillivirus).
Bacterial infections (brucella, erysipelas).
Parasitoses (toxoplasmosis, nematode worms).
Emerging pathologies linked to climate change.

Biomarker assays (such as cortisol) make it possible to assess the effects of environmental stress, of noise pollution or of contaminants.

Major bioindicators of marine contamination

At the top of food chains, cetaceans accumulate high concentrations of pollutants. Analysis of stranded tissues makes it possible to monitor:

Persistent organic pollutants (PCBs, dioxins, pesticides).
Heavy metals (mercury, lead, cadmium).
Emerging contaminants (flame retardants, PFAS).
Microplastics and marine debris.

These forms of pollution, often detected earlier in cetaceans than in humans, make marine mammals genuine ecotoxicological sentinels.

Worth noting: several species have lost a key enzyme for the detoxification of organophosphate pesticides, which makes them particularly vulnerable to certain agricultural pollutants.

Long-term scientific monitoring

The Réseau National Échouage (RNE), active since 1972, is one of the longest-running databases on marine mammals in the world. It makes it possible:

To follow the trend in strandings over several decades.
To detect unusual mass mortality events.
To produce indicators of relative abundance (despite the bias of the 8% of individuals that strand compared with those that die at sea).
To identify risk areas from spatial data.

The data also reveal seasonal dynamics and migratory movements.

A tool for understanding the effects of global change

Strandings make it possible to document the responses of cetaceans to:

Climate change (new ranges, temperature-sensitive diseases).
The intensification of anthropogenic pressures (shipping traffic, pollution, fishing).

They thus become a warning system on the functioning of marine ecosystems.

A reference base for conservation policy

The data from strandings feed directly into:

The Marine Strategy Framework Directive.
Conservation status assessments for species.
Management plans (exclusion zones, reduction of bycatch, post-measure monitoring).

They make it possible to measure objectively the impact of protection measures.

Prospects strengthened by emerging technologies

New approaches strengthen the scientific value of strandings:

Genomic analyses for fine-scale differentiation of populations.
Assays of stress and contamination biomarkers.
Stable isotopes to reconstruct food chains.
Environmental DNA (eDNA) to detect the presence of species from their biological traces.

The study of cetacean strandings is an essential lever for knowledge and surveillance of marine environments. It offers direct access to the major ecological issues of our time: biodiversity, pollution, climate, the health of ecosystems. As sentinel species, stranded cetaceans alert us to the state of the oceans and to emerging threats. Their rigorous monitoring is a strategic investment for understanding and protecting marine life.