How in Danger Is an Endangered Species? New Study Provides an Answer

The Endangered Species Act defines an endangered species as one that is “in danger of extinction within the foreseeable future throughout all or a significant portion of its range.” But what does that mean in terms of number of animals or actual risk of extinction?

A team of scientists set out to determine if they could find consistent thresholds for species listed under the Endangered Species Act. In other words, is there a consistent benchmark for what endangered actually means? They examined 14 marine species that have gone through the listing process and published their analysis The previous link is a link to non-Federal government web site. Click to review NOAA Fisheries disclaimer in the scientific journal Conservation Letters.

“We found that the endangered species really stood out,” said Charlotte Boyd, a postdoctoral researcher at NOAA Fisheries’ Southwest Fisheries Science Center and lead author of the new paper. “These were species that were really in serious trouble, already at critically low population sizes at the time of the listing decision.”

The scientists put numbers to it. In most cases, endangered species could be defined as species where the number of mature animals is at high risk of declining to fewer than 250 breeding adults within five generations – although some may merit a higher or lower threshold given their population ecology. Examples include Washington’s Southern Resident killer whales, with fewer than 100 remaining, or California’s black abalone, with so few left they may not be able to effectively reproduce.

“These criteria allow you to line these species up next to each other, and assess whether they meet consistent benchmarks,” Boyd said. “That information could be very useful to scientists who are assessing species in the future.”

One such scientist is Barbara Taylor, a marine mammal biologist at the Southwest Fisheries Science Center and a coauthor of the new study. She often sits on science panels evaluating species for listing under the ESA.

“Our job would be more efficient and transparent if we knew what level of risk equated to being considered ‘endangered’ or ‘threatened,’” Taylor said. “In an era of increased numbers of species needing protection, making efficient decisions in both determining which species need emergency attention and which can be released from emergency care is key to saving species for future generations.”

Under the Endangered Species Act, the next level of risk after endangered is threatened. Threatened species were harder to distinguish — their populations were larger or declining less rapidly than endangered species, but with few healthy subpopulations remaining, the study found. Examples include Puget Sound steelhead and Upper Columbia River steelhead.

The study’s findings could provide “a valuable basis for moving towards a more standardized approach to identifying endangered and threatened species under the ESA following formal statutory and policy review,” the scientists wrote. The results also “could be useful in guiding future status reviews and recovery plans.”

The scientists cautioned that all species are different, and decisions on whether to list species as threatened and endangered must independently evaluate the individual risks they face. But the new study may provide useful benchmarks in determining the degree of protection the species may need, they said. 

“Having quantitative benchmarks allows scientists to evaluate status more rapidly and consistently,” Taylor said. “With the number of species facing extinction accelerating, this translates into critical time to treat the species most at risk.”

An endangered black abalone Aerial photograph of an adult female southern resident killer whale
An endangered black abalone (top) and green anemone (bottom) sharing a rocky intertidal crevice at a Southern Channel Island off the coast of Southern California. The photograph was taken on November 14, 2012, during annual black abalone intertidal surveys led by the U.S. Navy and the U.S. Geological Survey with assistance from NOAA Fisheries and other partners. These surveys have been conducted for 35+ years and are critical for providing information on the status of black abalone, a species threatened by extinction due to a number of factors including historic overfishing, disease, future oil spills, and ocean warming. Photo Credit: NOAA Fisheries / Melissa Neuman WCRO. Aerial photograph of an adult female southern resident killer whale (J22), swimming next to her sub-adult son (J34, still growing) near the San Juan Islands, Washington State, U.S.A. Image demonstrates sexual dimorphism in body length and appendage size: see larger pectoral flippers, tail fluke and dorsal fin of male breaking the surface.Photograph obtained in 2016 using an unmanned hexacopter (e.g. Durban et al. 2015) flown at >100ft above the whales with permits from NMFS (# 16163) and airspace clearance by the FAA (2015-ESA-200-COA).Photo Credit: John Durban, Holly Fearnbach (NOAA/SWFSC) and Lance Barrett-Lennard (Vancouver Aquarium).

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