One of the research projects we are collecting samples for this summer is examining the response of Dolly Varden gut size to the pulse of sockeye eggs that are delivered to rivers each summer. In a recent study*, Armstrong and Bond demonstrated that Dolly Varden in the upper Alec River eat very little during the year before the arrival of spawning salmon, and then gorge themselves on eggs. They found that not only does the amount of food in their stomachs increase after salmon are in the streams, but that the size of the fish’s gut increase relative to their body weight. They have a physiological response to increase their capacity to take advantage of the annual pulse of sockeye eggs to their streams. This summer we are investigating the timing of this increase in gut capacity.
Not a bad way to spend an afternoon working, before returning to the lab to measure our sampled fish. The Dollies are pretty skinny at this time of year, but will be much fatter and more colorful (as they enter their spawning period) during our later samples.
* Armstrong JB and Bond MH. 2013. Phenotype plasticity in wild fish: Dolly Varden regulate assimilative capacity to capitalize on annual pulsed subsidies. Journal of Animal Ecology.