Animals are important sentinels, or forewarners, of ecosystem change.
Both dramatic and subtle changes in wild populations may forewarn us of alterations in ecosystems that may ultimately affect humans. Animal sentinels may predict changes in ecosystems resulting from habitat loss, fragmentation, degradation, or contamination. Loss of habitat can result directly in loss of species. As marine mammals are top predators in the marine ecosystem, they are potentially ideal sentinels of the aquatic ecosystem. However, as many of these species are pelagic, access to these animals is usually limited to stranded animals, which are far from a representative sample of the free-living population.