MetadataShow full item record
Due to overfishing, land-use change, and climate change, many freshwater salmonid populations are at risk or already imperiled. Research addressing the biological mechanisms behind habitat selection is important if these populations are to be protected and restored. A literature review of salmonid habitat selection models has shown there is a lack of habitat selection data that relate a fitness surrogate, such as energy intake, to habitat selection. Descriptive studies of habitat selection, such as comparisons between use and availability, generally cannot elucidate the actual mechanisms producing differential selection of habitats. To identify potential factors affecting the decline of Chinook Salmon (Oncorhynchus tshawytscha) in Alaska, we examined the relationship between reactive distance, prey capture success, and water velocity for juvenile Chinook Salmon and used these results test the net energy gain habitat selection model of Grossman et al. (2002). We conducted two experiments, the first with 27 fish between 58 and 84 mm standard length (SL) and weight between 2.8 and 7.5 grams, and the second using pairs of dominant and subordinate fish (i.e., larger and smaller, mean difference= 7 mm (SL)) to test for the effects of dominance on prey capture success. Using an artificial stream tank, we tested juvenile Chinook Salmon at 10 cm/s velocity increments (10 cm/s to 60 cm/s) using frozen brine shrimp (Artemia spp.) as prey. Reactive distances for single fish trials averaged 32.7 cm and did not show significant velocity effects (p=0.66). Velocity was inversely related to prey capture success in a non-linear manner (p<0.001) and we found a significant difference between fish holding velocities and prey-capture velocities (p<0.001). Using the Grossman et al. (2002) model, we predicted that 35.4 cm/s should be the optimal focal-point velocity for juvenile Chinook Salmon. Analyzing videos of juvenile Chinook Salmon in the Chena River, we found they occupied a microhabitat velocity of 12 cm/s, most likely due to the effects of predation. The dominance experiment indicated there was no significant difference in reactive distances between dominant and subordinate fish (p=0.16) but dominants captured significantly more prey than subordinates (p<0.001). Holding velocities for dominant and subordinate fish were significantly different than prey-capture velocities (p<0.001) and there was no significant difference between the dominant (26.3 cm/s) and subordinate (21.4 cm/s) holding velocities (p=0.47).