In an environmental news cycle typically dominated by calamity and existential threats, it’s an absolute joy to report a significant bit of very good news released last week. Scientists from the Center for Biological Diversity recently concluded a study that found most marine mammals and sea turtles protected under the Endangered Species Act are recovering and moving toward healthy, stable populations.

The study collected population data on 23 different marine mammals and nine species of sea turtle. Specific species were chosen when there was sufficient data to make a reasoned analysis. A full 78 percent of the species examined, from Florida manatees to California sea otters, had seen very promising population growth since falling under federal protection.

Conservation law works.


The Endangered Species Act, written into law in 1973, protects habitat, reduces trade and harvesting, provides science-backed pathways to recovery, and works to lessen the harm done to endangered animals by human activity like energy extraction, pollution, and military maneuvers.

Humpback whales are migrating along the West Coast in numbers not seen in generations (many species of humpbacks were removed from the endangered list in 2016), Steller sea lions are rebounding well, and Floridian sea turtles like the loggerhead and leatherback are surpassing population records.

In most cases, the longer the animals were on the endangered list, the better they’ve recovered.


“Overall, species listed for 20 or more years were more likely to increase in population abundance,” the study’s authors reported.

The California sea otter has rebounded in numbers so successfully that it may soon be removed from the endangered list altogether.

How do they count, you may be wondering?

“Population abundance for marine mammals and sea turtles can be estimated through aerial, land, and ship-based visual surveys,” Dr. Abel Valdivia, lead author of the study told us. Sea turtles’ numbers can be figured from the amount of nesting females counted and how many eggs they lay. It can be more difficult for big whales that spend huge amounts of time far underwater. “When this happens, population abundance can be estimated based on mark-recapture population models, extrapolating data based on sex ratios, photo-identification models, among other specific population modeling efforts,” Dr. Valdivia said.


“The Endangered Species Act works. This is great news at a time when our oceans face growing threats from climate change, overfishing, and pollution,” Dr. Valdivia explained. “It’s easy to get discouraged as we watch human activities destroy marine ecosystems. But our study shows we can still save whales and other endangered species if we just make the effort.”

Only two species were shown to have experienced continued decline. Southern resident killer whales and the Hawaiian monk seal both continue to have alarming depopulation trends.

But overall, this latest study is evidence that problems plaguing marine mammals: overfishing and prey reduction, pollution, climate change, and habitat loss can be mitigated and even reversed.

The Center for Biological Diversity’s study is under review by the journal PLOS ONE.

Photo: Christopher Michel

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