A new study conducted by researchers from the University of Alaska on a creek in the Southeast part of the state has revealed that pink salmon are adapting over time to migrate earlier, a response to warming waters associated with climate change. The study has major implications for explaining how animals in the wild are adapting to warming climes and which animals might be falling behind.
The researchers looked at populations of pink salmon in Auke Creek -- near the state's capital, Juneau -- taking advantage of a genetic marker that another researcher had used to monitor early and late-run salmon populations in the 1980s.
That researcher, UAF Fisheries and Ocean Sciences professor Anthony Gharrett, bred a genetic marker into a select population of late-arriving Auke Creek pinks beginning in 1979. He aimed to use the genetic marker -- which neither helped nor hurt the fish evolutionarily -- to monitor the late-migrating pink salmon run in the creek.
Gharrett is included as one of the authors of the recent study, along with UAF's Ryan Kovach and University of Southeast's David Tallmon.
Kovach said that the ability to use Gharrett's markers to gauge genetic evolution was a "fortuitous coincidence," but that Gharrett also worked closely with the other researchers on the project.
Auke Creek used to have two distinct runs of salmon, Tallmon said. One would arrive in mid-August, and the other would arrive in mid-to-late September. In the 1980s, the presence of the genetic marker in the overall population was relatively stable, but suddenly declined beginning in 1989. This meant that the late-arriving salmon were disappearing -- not eaten by predators, but being displaced by evolution.
1989 saw the second-highest stream temperatures on record, the study says, a strong indicator that the salmon were adapting to arrive earlier to compensate for increased water and climate temperatures. Now, Tallmon said, the runs seem to have melded into a single run, earlier in the year.
Study co-author Kovach said that there were far fewer late-migrating salmon coming into Auke Creek.
"The result of this is that pink salmon are migrating into Auke Creek for approximately 15-20 days fewer days than in 1971," Kovach said. "In other words, our earliest data show that migration tended to occur over a period of 60 days, but in recent years the primary migration event has taken place over 40-45 days."
What does it mean for other Alaska salmon?
So why pink salmon?
"Pinks are sort of the lab rats of salmon," Tallmon said. "They have a two-year life cycle and they're locked into that cycle."
That two-year life cycle means that the fish can evolve quickly to adapt to changing climate patterns. The fact that there are two distinct populations out of the same creek -- one that arrives on odd-numbered years, another that arrives on even-numbered years -- also helped show that the reduction of the genetic marker wasn't limited to one population.
Tallmon said that the odd- and even-year populations would have little opportunity to mix.
"They could overlap somewhat but probably not a ton," he said. "They're independent breeding populations that occupy the same space."
But for both populations, Tallmon said, "What seemed to be two distinct runs seem to have blended into a single run."
"Specifically," the study reads, "we observed that both even- and odd-year adult pink salmon that spawn in a warming Alaskan stream are migrating into freshwater earlier and are migrating over a shorter period of time."
The results of the study may mean bad news for other types of salmon, which can have longer lifespans than the two-year pinks. King salmon and cohos, Tallmon said, can have 3-5 year lifespans.
In a year such as this one featuring precipitously low runs of kings, the research is significant, since the longer-lived salmon might not be adapting quickly enough to compensate for the relatively rapid rate of climate change in their habitat.
The study noted that the earlier-migrating pinks also appeared to be healthier in years with warmer temperatures, which is counter to traditional salmon runs.
"Migrating pink salmon appear to avoid high stream temperatures;" the study said, "given the trend in migration timing, changes in the genetic marker and increasing stream temperatures in Auke Creek, it appears that earlier-migrating fish may have higher fitness in warmer years."
Asked whether the slower rate of generation turnover among other types of wild salmon might have something to do with declines in recent years, Tallmon said that it's "definitely a possibility."
Kovach said that the hard research isn't there, but agreed that it's something to consider.
"At this point," Kovach said in an email, "I am not aware of any data that suggest that decreasing runs of other Alaskan salmon populations are due to a lack of evolutionary change in response to climate warming, but the possibility for this is an interesting question for future research."
More research may be what it takes. But Alaska's fishermen might someday find themselves hitting the streams earlier than ever before.
Contact Ben Anderson at ben(at)alaskadispatch.com