Why might you find scientists out on a pitch black night on a remote Alaskan lake driving two 18’ boats with a net towed in between? Fun, tradition, data collection? Well, all of the above, assuming the weather is nice. In our article, “Climate variation is filtered differently among lakes to influence growth of juvenile sockeye salmon in an Alaskan watershed,” we rely on generations of scientists doing just this to evaluate how juvenile salmon growth responds to climate variability.
Long-term datasets provide opportunities to disentangled pattern from noise. Establishing and maintaining long-term datasets requires marshalling the human, financial, and logistical support necessary to return year after year to collect data. The University of Washington’s Alaska Salmon Program (http://fish.washington.edu/research/alaska/ or https://www.facebook.com/AlaskaSalmonProgramFRI) has been sending scientists to remote southwest Alaska since the mid-1940s to collect data on juvenile sockeye salmon and their habitats.
Our field methods today are remarkably similar to those established over 60 years ago. Every summer at the end of August, we head out onto our study lakes (in this case, Chignik and Black lakes) on small boats just as the sun is heading down. Armed with a net that looks a like a gigantic windsock with arms, flashlights, a GPS, and trays and buckets, we get ready to capture and measure juvenile sockeye salmon. Juvenile sockeye salmon feed near the surface at night making them more easily sampled by our nets. We tow the net between our “master” and “slave” boats according predetermined tracks, hoping to steer far clear of shore. After towing for a set time, we haul in the net and inspect our catch. Fish we catch are subsampled and brought back to our field station to be measured and weighed.
By sampling year after year, we can observe the variation in juvenile sockeye salmon growth during their first summer of life and evaluate causes of variation in growth. Growth is an important determent of their ability to avoid predators as well as survive winter conditions and ocean migration. In our study we investigated if the year to year variability in growth was explained by climate variation, including differences among years in winter and spring air temperature. Using additional information regarding juvenile salmon growth collected from adult sockeye scales, we were also able to investigate whether the same regional climate such as air temperature elicits the same growth response from juvenile salmon in different lake types.
We found that the average size of juvenile salmon has been increasing over time. However, the same changes in air temperatures did not always lead to the same response in juvenile salmon growth in different lake types. Juvenile sockeye salmon grew larger in years with warmer spring and fall temperatures in deep, cold Chignik Lake. Just upstream in shallow, warm Black Lake, juvenile salmon grew less in years with warmer air temperatures. These differences in growth indicate that landscape diversity within watersheds filters climate such that organisms experience and respond differently among habitats. Our ability to manage for resilient ecosystems in the face of ongoing environmental change may be improved by considering within, as well as among, watershed climate filtering.