University of Washington fisheries scientists have completed a new study documenting why two of Alaska’s most productive salmon populations and the fisheries they support depend on the entire watershed for habitat.
The study, which appeared on May 24 in the journal Science, looked at chemical signatures imprinted on tiny stones that form inside the ears of fish, and found that sockeye and Chinook salmon born in the Nushagak River and its network of streams and lakes use the whole basin as youngsters to find the best places for prey, shelter and safety from predators for the first year of their lives, until they migrate into the ocean.
By analyzing that ear stone, called an otolith, researchers found that different parts of the watershed are hot spots for salmon production and growth, but that these favorable spots vary from year to year, depending on how climate conditions interact with landscape features like topography to impact the value of habitats.
The Nushagak River watershed, the largest river basin in the Bristol Bay region, supports the biggest sockeye salmon fishery in the world and provides about 50 percent of wild sockeye globally. The watershed is also known for its large run of king salmon.
Release of the study comes as the U.S. Army Corps of Engineers is taking comments on its draft environmental impact statement prompted by a global Canadian mining company’s effort to build a massive copper, gold and molybdenum mine in the Bristol Bay watershed. The study was also reported by EurekAlert, the online publication of the American Association for the Advancement of Science.
The study was funded by Bristol Bay Regional Seafood Development Association, the Bristol Bay Science Research Institute and the Arctic-Yukon-Kuskokwim Sustainable Salmon Initiative.
The draft EIS environmental analysis considered only two or three years of fish counts in specific locations in proximity to the proposed mine, and states that fish habitat lost to the mine could be recreated elsewhere. The study, however, shows that key salmon habitat shifts year to year, and how productive a specific area may be for a short time might not represent its overall value to the fish population or larger ecosystem.
“We found that the areas where fish are born and grow flicker on and off each year in terms of productivity,” said Sean Brennan, a postdoctoral researcher at the UW School of Aquatic and Fishery Science and lead author of the study. “Habitat conditions aren’t static, and optimal places shift around. If you want to stabilize fish production over the years, the only strategy is to keep all of the options on the table.”
“The overall system is more than just the sum of its parts, and small pieces of habitat can be disproportionately important,” said Daniel Schindler, a professor at the UW School of Aquatic and Fishery Sciences and senior author of the study. “The arrows point to the need to protect or restore at the entire basin scale if we want rivers to continue to function as they should in nature.”
By looking at each fish’s otolith, which accumulates layers as the animal grows, the research team could tell where that fish lived by matching the chemical signatures imprinted on each “growth ring” of the otolith with the chemical signatures of the water in which they swam.
“Essentially, we’re sampling the entire watershed and letting the fish tell us where the habitat conditions were most productive in that year,” Schindler said.
“The big thing we show is these types of dynamics are critical for stabilizing biological production through time,” Brennan said. “When you have a range of habitat available, the total production from the system tends to be more stable, reliable and resilient to environmental change.”
Brennan and Schindler said they hope their study can be used to inform the scientific analysis of the proposed mine’s impact on fish.
“Results like those we’re presenting in this paper hopefully will get people to think about what they stand to lose by starting to develop and eliminate habitat in places like the Nushagak River,” Schindler said. “The Pebble mine environmental impact statement, which is supported to be a mature, state-of-the-science assessment of risks, really does a poor job of assessing risks of this specific project.”The public comment period for the proposed mine’s draft EIC was recently extended to July 1, to provide more time for everyone interested in the proposed mine to comment on the 1,400-page draft EIS.
