Endangered Marine Species Populations Bounce Back

A bit of hopeful news was released last week: Marine mammal and sea turtle populations have increased significantly after being protected under the United States Endangered Species Act (ESA). This is according to a recent study conducted by the Center for Biological Diversity in California and published in PLOS ONE.

Enacted in 1973, the ESA is credited with preventing extinction and promoting the recovery of imperiled plants and animals. Species protected under the ESA are typically targeted by tailored federal and state conservation efforts with increased funding for management.

As extinction risk in the oceans has increased due to the degradation of ocean ecosystems, a growing number of marine species have been added to the list and subsequently protected under the law. As of August 2018, there were 163 marine species listed as threatened or endangered, but little quantitative research data have been available about recovery trends for endangered marine mammals and sea turtles. Some of the protected mammals, such as the blue whale, humpback whale, Florida manatee, and leatherback turtle had been on the list for more than 45 years.

To find some answers, Abel Valdivia, PhD, an ocean scientist at the Center for Biological Diversity in Tucson, Arizona, and his colleagues analyzed population trends, the magnitude of population change, and recovery status for 23 representative populations of 14 marine mammal species and 8 representative populations of 5 sea turtle species.

The study’s findings suggest that conservation measures, including tailored species management and fishery regulations, have been largely successful in promoting recovery. The efforts have even led to the delisting of some species and to increases in most populations.

Specifically, 18 (78%) marine mammal populations and 6 (75%) sea turtle populations have increased significantly after ESA listing. Conversely, 2 (9%) marine mammal populations declined after ESA protection, but this did not include any sea turtles. Overall, however, the 24 populations that increased in abundance were from species listed for 20 years or more, including large whales, manatees, and sea turtles.

Case studies within the group’s research highlight the positive impact of being on the ESA list. For instance, Hawaii’s humpback whale population grew from just 800 in 1979 to more than 10,000 by 2005.

According to the investigators, the results underscore the capacity of marine mammals and sea turtles to recover from substantial population declines when conservation actions are implemented in a timely and effective manner.