Since it is not possible to precisely count all debris items in the marine environment and to assess all their impacts on marine fauna, we use bio-indicators which provide information on the environmental state of the environment and therefore on the efficiency of some environmental measures.
What is a (good) indicator?
In the case of marine litter, a good bio-indicator should reflect the spatial and temporal variations in litter impacts according to pollution levels. Therefore, it provides a way to evaluate the efficacy of policy measures aimed at reducing litter input into the oceans. To be effective, a good indicator must be accurate, sensitive, reliable and easy to use for all the stakeholders in order to be applied to a large geographic area.
Sea turtles, cetaceans and fish are considered good bio-indicator taxa for measuring the impacts of debris on marine wildlife because they;
tend to ingest or become entangled in marine debris
have a large spatial distribution
use all ecological marine compartments
(from bottom to surface of oceans)
Furthermore, in most regions, a sufficient number of stranded or accidentally captured animals are observed and can provide information’s in the framework of a monitoring programme.