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 are considered a good bio-indicator species for measuring the impacts of debris on marine wildlife for at least three reasons:
turtles tend to ingest marine debris
they have a large spatial distribution
they use all ecological marine compartments
(from bottom to surface of oceans)
Furthermore, in most regions, a sufficient number of stranded or accidentally captured turtles are observed and can provide information’s in the framework of a monitoring programme.
The indicator “debris ingested by sea turtles” has been proposed as a relevant indicator for monitoring ocean status. However, more scientific knowledge is need to evaluate its criteria of use, that will make it a precise and robust indicator. In addition, other indicators must be developed in order to measure other types of impacts of debris on sea life, such as entanglement or micro-debris ingestion (<5 mm).