Listing and delisting of species under the endangered species act (ESA) is a delicate political and scientific dance that can play out over decades. Anyone who has paid attention to the listing, reintroduction, and delisting of the grey wolf has some idea of how this often plays out. The politics and policy of the ESA are always complicated, that is expected.
But things get very interesting when the population itself is changing quickly; when climate, conditions and management change the game even as it is being written. This is the intriguing case of the Snake River fall Chinook salmon.
Fall spawning Chinook salmon in the Snake River of Idaho are the big dogs of the salmon world. Chinook routinely grow as large as 40-50 pounds. Historically they spawned in the main stem of the Snake River from the mouth to Shoshone Falls in Southern Idaho, more than 900 miles from the ocean. In these spawning areas warm and productive water allowed them to grow extremely quickly, while high summer temperatures selected for early “ocean type” outmigration to the ocean. Being extremely numerous, and spawning during low water periods when they were easier to catch, they made up the majority of the native salmon harvest.
…in 1916 it was estimated that 460,000 fish returned to the Snake River. By 1966 this number was down to 19,500 fish…By 1990 only 78 wild adult fish were spotted at Lower Granite Dam.
Harvest and dams changed this reality drastically, as has been the case for salmon populations everywhere. Placing numbers on how many fish existed before the dams is difficult but, for some perspective, in 1916 it was estimated that 460,000 fish returned to the Snake River. By 1966 this number was down to 19,500 fish. This was nine years after the failure of fish passage in Hells Canyon blocked passage to the most productive spawning areas in southern Idaho, and many years since harvest had begun to decrease populations from their historical levels. By 1990 only 78 wild adult fish were spotted at Lower Granite Dam. In 1992 Snake River fall Chinook were listed as threatened under the ESA and a hatchery program was well underway to try to restore the population.
If this sounds depressingly similar to the stories of the drumbeat of species under threat due to anthropogenic changes, hang with me. It’s the story since 1992 that gets interesting.
While the march of the ESA has proceeded slowly through the inevitable lawsuits and countersuits Fall Chinook have been playing by their own rules.
In the early 2000’s managers began to notice that this population, unique in it’s singular “ocean type” migration history, was displaying some alternate migration behavior. Large juveniles were being caught in the very early spring at the dams, an entire winter later than juveniles usually moved to the ocean. In fact, it appeared in several studies that these late migrating fish might be surviving to adulthood at a greater rate than their early migrating peers. What was going on here?
For some perspective it’s worth thinking about the habitat these fish now occupy. In a free flowing river, optimal growth occurred upstream, but summer temperatures were lethal in both the spawning areas and in the lower river…creating a clear selective advantage to fish that migrated early. This was no longer the case.
Having been cut off from their upstream habitat, fish were forced to spawn in generally cooler habitat in the Snake and the only other available spawning habitat was in the much cooler Clearwater River. Meanwhile, managers were letting millions of gallons of cold water flow down the Clearwater River from Dworshak reservoir to save smolts whose trip to the ocean was delayed by the need to swim through slack water in the reservoirs.
Cooler spawning areas create later hatches, as much as a month later in the Clearwater river. Cool water releases in the summer months provided a way to survive the summer months that had been lethal in the past. Slack water reservoirs were already forcing juveniles to spend more time in the reservoirs. Presumably the productivity of the reservoirs was different than the free flowing river had been, perhaps providing a food source. Clearly there was evidence of a changing fitness landscape.
Clearly there was evidence of a changing fitness landscape…One study indicated that this had the potential to be more than simple adaptation; this could be an example of fast evolution of behavior.
Science backed this up, with some studies correlating the differences in temperature with the likely migration timing changes. Another study showed that a majority of the late migrating juveniles came from the Clearwater, the coolest and latest hatching spawning area. One study indicated that this change in migration had the potential to be something more than simple adaptation; this could be an example of fast evolution in behavior.
Meanwhile state and tribal hatcheries were producing millions of fry and redds (salmon nests) were beginning to fill the rocky bars of the Clearwater River, habitat they never historically took such heavy advantage of. At the same time ocean conditions were favorable, with the Pacific Decadal Oscillation (PDO) creating the cooler ocean conditions off the western coast that correlate with good salmon returns.
Fall Chinook numbers took off and continued to climb. By 2013 over 20,000 naturally reproducing adults were returning to the Snake River and both hatchery and natural fish combined for a total of 75,846 fish.
This recovery is remarkable. Remarkable enough that in April of this year NOAA responded to a petition to delist Fall Chinook made by an Alaskan fishing group. Of course this does not mean that Snake River Fall Chinook will be coming off the endangered species list any time soon. It only means that NOAA will undergo a status review, and…since NOAA has not been able to finalize a recovery plan due to prior lawsuits and delays it’s unlikely they will be delisted before then.
Still, what are we to make of this remarkable recovery? With the PDO heading into a warm phase, creating poor ocean conditions, can we expect the same level of returning fish in the future? No one is certain. Further, how much of a role should hatcheries play in providing a sustainable population, if at all? Clearly, the current numbers owe a lot to the efforts of hatcheries but no one is sure if the end goal is a fully sustainable population or one supported by hatcheries. Is it possible for the population to be fully self-supporting in only fifteen percent of its former range?
Finally, what are we to make of this remarkable change in the migration behavior of the population? The ESA indicates that managers must preserve diversity within the population, but there are precious few examples of new diversity appearing after listing. These fish were originally defined as “ocean type”, to what degree will the final recovery plan recognize the new changes in the population? How much of the recovery do we owe to this incredibly fast behavioral change?
Whether this is an evolutionary change or a plastic adaptation, will it help the population to persist in the future and in the face of climate change?
Beyond those questions this story highlights that, as ecologists, we work within systems that are complex and ever changing. While many population changes don’t move at a faster pace than our recovery efforts, change is inevitable and exciting. It’s easy to get caught up in the day-to-day of fieldwork and data analysis and forget this larger truth. When it comes up and slaps you in the face with a big, slimy, tail it’s a nice wakeup call to the incredible ways that natural systems work to adapt in a changing environment.