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Marine Animals Listed on Endangered Species Act Show Signs of Recovery

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A leatherback turtle preparing to nest (Photo: Shutterstock)

Turtle and marine mammal populations have seen a significant increase in recent years, thanks to their listing under the US Endangered Species Act (ESA), according to a recent report published in the peer-reviewed PLoS online journal.

Lead author Abel Valdivia of the Center for Biological Diversity in Oakland, California and his team collated the best available population data for the 62 marine mammal and sea turtle species that are listed under the ESA. A total of 163 marine species are currently protected under the act. The focus of the study was placed on 23 representative populations of marine mammals, comprised of 14 different species, and eight populations of five different turtle species. All of the species studied inhabit and reproduce in US waters, and have all been listed on the ESA prior to 2012.

Through quantitative analysis of the population trends over time, the researchers found that 18 populations of marine mammal and six populations of turtle had 'significantly' increased in size after being listed on the ESA. Three mammalian and two turtle populations showed 'non-significant' changes, and 2 mammal populations - but no turtle - populations had declined. According to the report, 'conservation measures triggered by ESA listing such as ending exploitation, tailored species management, and fishery regulations, and other national and international measures, appear to have been largely successful in promoting species recovery.' 

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Florida manatees are also among the populations showing signs of recovery after ESA listing (Photo: Shutterstock)

The most substantial increase in populations occurred in species that had been listed by the ESA for more than 20 years. Marine mammals such as bowhead whales, grey whales and humpack whales, manatees and seals have all increased in numbers in most locations that were studied.

Turtle species included in the report include hawksbill, green, Kemp ridley, leatherbacks and loggerheads. Some of the turtle populations have grown slowly over time, with the report listing green turtle nests at East Island of the French Frigate Shoals in Hawaii as having risen from 101 individuals in 1978 to 492 individuals in 2015. In other areas, the rebound has been much more dramatic. Turtle nests across Florida's beaches have recovered from 62 nests in 1979 to a record 37,341 nests in 2015, leading to the entire North Atlantic population of green turtles to be 'downlisted' from 'endangered' to 'threatened.'

 

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Turtle populations over time showing year of ESA listing and margin of error in grey. Click for larger image. (Image: Valdivia et al/Creative Commons)

The reasons for the recovery include prohibition under the ESA of harvesting turtles and their eggs, hence the excellent recovery across Florida. Fishery regulations also reduced the bycatch of turtles through 'changes to fishing gear modifications, major changes in fishing practices, time and area closures, and the establishment of turtle excluder devices for shrimp trawlers.'

The result is undoubtedly a conservation success story, but clearly there is plenty of work yet to be done. Affording legislative protection to a species can only work if it is actively enforced. Given that many aquatic animals are migratory, population recovery in one location may be hindered by lack of regulation in another. Leatherback turtles, for example, migrate from the Pacific US coast to Indonesian water, where they are not guaranteed the same level of protection.

'Significant population increases for most marine mammal and sea turtle species after ESA protection demonstrate the capacity of these taxa to rebound from drastic population declines after decades of exploitation, habitat degradation, and other threats, once effective conservation measures are in place,' states the report. Nevertheless, as the report also shows, it takes time.

 


Original publication: Valdivia A, Wolf S, Suckling K (2019) Marine mammals and sea turtles listed under the U.S. Endangered Species Act are recovering. PLoS ONE 14(1): e0210164. https://doi.org/10.1371/journal.pone.0210164

 

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