A stranding occurs when a marine animal gets washed ashore and is unable to return to the sea on its own. Dead stranded animals are considerably more frequent than alive ones. When dead, animals can exhibit different degrees of decay. If alive, they display unusual behaviour on account of stranding induced stress. 

Strandings, whether deriving from natural or anthropogenic causes, results from the confusion, debilitation and even death of marine animals. Among the natural causes are infectious and parasitic diseases, lack of food, intoxication (associated with biotoxins produced by algae blooms), weather conditions, oceanographic phenomena and even atypical individual behaviour. Exposure to chemical or noise pollution, garbage ingestion (e.g. ingestion of plastic bags by sea turtles) and direct contact with vessels (collision or fishing operations) comprise the most direct anthropogenic causes. Among these, the interaction with fishing gear has been the one that has deserved the most attention and raised growing concern given the environmental and economic repercussions.

In Portugal, as in many other countries, there has been an increase in the number of strandings per year recorded. Such pattern is related with alert promptness and efficiency from all parties involved, from institutions to citizens, often hinged by local stranding networks available 24/7.

The amount of information that can be gathered from stranded animals consists of a vital contribution to the scientific knowledge regarding such hard-to-monitor oceanic and often threatened species. Furthermore, considering that only a minor portion of dead marine animals actually gets washed ashore and is consequently spotted by humans, such events provide vital and relevant information in scientific areas such as biology, ecology, veterinary, pollution and fisheries management.