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When Is a Species Extinct? It’s More Complicated Than It Seems

Two UC Davis scientists say that there are at least five “gray areas” when looking at species extinction, which form a crucial distinction when assessing how to help protect endangered species and their habitats.

Written by Peter Moyle, Jason Baumsteiger Published on Read time Approx. 6 minutes
Tiny endangered delta smelt, which are nearly extinct in the wild, are researched at the U.C. Davis Fish Conservation and Culture Lab. The lab is located 80 miles from the Davis campus on the grounds of the California Department of Water Resources, John E. Skinner Delta Fish Protective Facility, near Byron, California, in Contra Costa County.Dale Kolke/California Department of Water Resources

We projected a bleak future for many freshwater fish, especially in California. Some difficult decisions will need to be made to prevent extinctions or to verify them. However, these decisions will rely on answers to one sweeping question: When is a species, in fact, extinct?

Some may argue this is a simple black/white or presence/absence question. But is it really? What if the species’ existence depends completely on humans? What if it no longer exists in its natural habitat or in the wild? What if it has been hybridized or genetically engineered? In such cases, is it fair to say this species is still the same as its wild predecessor?

In our recent paper, we attempted to tackle these questions and provide an honest, although imperfect, way to assess extinction. The first involves accepting that “gray extinction” exists. This is an area between formal threatened/endangered status and global extinction, where a species is in limbo – it is partially extinct. We know this sounds weird because under traditional usage, extinction is an all-or-nothing proposition. However, there are in fact gray areas. They fall into five categories. Each represents ways in which a species may be partially extinct. These categories are by no means exhaustive, but do represent a reasonable framework where partial extinction can be examined closely. We look at these categories through the eyes of biologists trying to conserve species through either a single-species or a multi-species approach.

Categorizing ‘Gray Extinction’

Chinook salmon smolts are released from a tanker truck on March 25, 2014, in Rio Vista, Calif. Due to habitat impacts, winter-run Chinook are an example of a species that depends on human intervention for survival. (AP/The Sacramento Bee, Randy Pench)

Mitigated extinction. This category represents the many ways in which a species can become dependent on humans for its existence. The formal term is “conservation-reliant,” but it just means that if we are not there to provide support, the species will quickly become globally extinct. Actions might include protection from predators, protection of habitat or even finding mating partners. Winter-run Chinook are a good example: They depend on humans for spawning habitat and early life-history protection (food, predator and disease avoidance). Without human intervention, winter-run Chinook (thanks to the Shasta Dam) would quickly cease to exist.

Regional extinction. Here we are talking about what happens when a significant portion of a species’ range has been lost. Now you might say, isn’t that just extirpation? To which we would say, not necessarily. Regional extinction applies when a very distinct portion of that range is lost, such as a region occupied by a distinct population segment (DPS) or an evolutionarily significant unit (ESU). In California, a good example is the isolated population of bull trout that once existed in the McCloud River, which became extinct in the 1970s. The species is still widely distributed and a threatened species in much of its range, but it is now absent from California.

Native-range extinction. As the name implies, this is a species that no longer exists in its natural range but may exist elsewhere (say, a reservoir somewhere). So while there are “wild” fish swimming about, they are not in the area in which they originally evolved. In California, Sacramento perch have disappeared from their native habitats in Central California. However, they were planted around the West as a game fish that could live in alkaline waters, developing large populations in places such as Crowley Reservoir in the Owens Valley or Pyramid Lake in Nevada.

Wild extinction. This category is one step further than native-range extinction. Now the species exists only as a captive population (think hatchery or zoo). Delta smelt are dangerously close to falling into this category.

Apparent extinction. This category is the final “holding pattern” category, when we think the species is globally extinct because we cannot find it anywhere. However, we want to wait to be sure. We talked briefly about this in part one of the blog. Right now, the International Union for Conservation of Nature (IUCN) tells us to wait 50 years before declaring extinction, but there is a big difference between species with 1-year vs. 25-year generation times. Therefore we propose a waiting period based on generation time: 1–5 years = 10 generations; 5+ years = 5 generations.

Single-Species vs. Multi-Species Approaches

We have determined it is time to act. But how best to do so? The current agency approach is based on single species (per the Endangered Species Act). As a species becomes endangered, we start doing everything we can to conserve that species, one species at a time. But as we mentioned, the endangered list is growing quickly. These approaches will become cost-prohibitive as the list gets too big. And by law, work must continue until that species is “recovered,” which could essentially mean forever for many species. Instead we argue for taking a multi-species approach to conservation. Go in and restore the original habitat (or at least a reasonable portion of it). This saves both the species in peril and all the species that naturally coexist with it. This might incur a huge cost initially, but if done right would be a one-time cost that returns native fish to their native habitat in abundance. In other words, restore the system, not just the numbers.

It is very important to note that we are not against human involvement in the saving of species. By no means! We are all for it. Some action is better than doing nothing. We simply want to stress the need to engage in conservation strategies that keep natural species in their natural habitats, where they can undergo natural selection for as long as possible. Administering artificial selection to save them, putting the species into “gray extinction,” should be a last resort. And we felt it is important to distinguish between those species that have been subject to such methods (artificial selection) from those that have not. The latter would seem to have a greater chance of survival in the wild. More information improves decision-making.

When we put these ideas together, we generated a decision tree to help navigate the many categories and approaches that one might take in assessing extinction. This tree starts with the basic, but big, assumption that our society really wants to prevent more extinctions. Again our purpose is to show the pathways from traditional threatened/endangered listings to global extinction – or as the case may be, to conservation successes. Our decision tree has checkpoints throughout, which would be a great place for biologists and stakeholders to sit down and assess progress and future approaches. We recognize that this is not an all-inclusive look at all-things extinction, but we do see it as a starting point to better management of species at every level.

In an era when the integrity of science is being questioned, we can no longer afford to hide these facts and avoid these difficult questions. Transparency is paramount. People need to know how complex the issues are and what we are facing. Our paper is an attempt to meet this growing need, to lay our cards on the table to show what managers are up against when it comes to assessing extinction. Regardless of politics, we are all part of and depend on the same global ecosystem. How long should we allow species to drop out of that system before we become concerned? Extinction is very real, very permanent and the numbers in the gray area are increasing. The time is now to focus on these species before the slide accelerates. After all, decisions to save species from now on will only become increasingly harder.

This story first appeared on California Water Blog, published by the UC Davis Center for Watershed Sciences. It is the second of a two-part series. You can read part one here.

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