If you have journal access, see the paper here or e-mail me for a reprint.
As part of our research into the diversity of anadromous behavior in Dolly Varden, we initiated a study of Dolly Varden movements (mainly ascent into freshwater in summer and fall) on three different spatial/temporal scales. First, we used acoustic tags to identify when fish were moving from lagoon to fresh waters in the Chignik system (see photo below). We found a very bi-modal distribution, with some fish entering freshwater in mid-summer, shortly after tagging. A second group of fish entered as late as November.
A second aspect of the study involved comparing upstream migration timing in the Chignik system to that of other watersheds throughout Alaska. In many watersheds weirs (see the Chignik Weir, the largest in Alaska, below), acoustic counting stations, or fish wheels are used to enumerate upstream passage of salmon. Sometime Dolly Varden are also counted (Sadly, Dolly Varden are not counted, or are counted but never entered into databases or published in many watersheds where monitoring occurs) and we can learn something about the median date of upstream migration in those systems.
It turns out that although there is a general latitudinal cline in migration timing, with fish in higher latitude streams returning later than those in low latitudes. This may be because at low latitudes fish enter coincident with salmon for egg/flesh feeding opportunities, while at high latitudes they remain in marine waters for feeding for as long as possible.
An additional analysis of the few streams that we have long-term data for indicate that nearshore ocean temperatures are correlated with variation in return timing. In systems where fish return before the peak temperature, warms years tend to drive fish upstream early, while in streams where fish return after peak temperatures, fish tend to return later in the warm years.
Together these analyses paint a clearer picture of the complex migratory patterns of Dolly Varden that Bob Armstrong labeled as the “manager’s nightmare” in a 1984 paper.