Marine mammals and sea turtles listed under the U.S. Endangered Species Act are recovering

Abstract

The U.S. Endangered Species Act (ESA) is the worlds strongest environmental law protecting imperiled plants and animals, and a growing number of marine species have been protected under this law as extinction risk in the oceans has increased. Marine mammals and sea turtles comprise 36% of the 161 ESA-listed marine species, yet analyses of recovery trends after listing are lacking. Here we gather the best available annual population estimates for all marine mammals (n=33) and sea turtles (n=29) listed under the ESA as species. Of these, we quantitatively analyze population trends, magnitude of population change, and recovery status for representative populations of 23 marine mammals and 9 sea turtles, which were listed for more than five years, occur in U.S. waters, and have data of sufficient quality and span of time for trend analyses. Using generalized linear and non-linear models, we found that 78% of marine mammals (n=18) and 78% of sea turtles (n=7) significantly increased after listing; 13% of marine mammals (n=3) and 22% of sea turtles (n=2) showed non-significant changes; while 9% of marine mammals (n=2), but no sea turtles declined after ESA protection. Overall, species with populations that increased in abundance were listed for 20 years or more (e.g., large whales, manatees, and sea turtles). Conservation measures triggered by ESA listing such as ending exploitation, tailored species management, and fishery regulations, among others, appear to have been largely successful in promoting species recovery, leading to the delisting of some species and to increases in most. These findings underscore the capacity of marine mammals and sea turtles to recover from substantial population declines when conservation actions under the ESA are implemented in a timely and effective manner.