First documentation of pelagic larvae of Prickly Sculpin Cottus asper in Willamette Basin reservoirs using a novel light trapping method

Although sculpin can play important ecological roles, serving as abundant key meso-predators in freshwater aquatic systems, much remains to be learned about their development and ecology. Depth discrete light traps effectively captured larval sculpin from Lookout Point Reservoir in the Willamette Basin, Oregon, USA. We confirm that these larvae were Prickly Sculpin (Cottus asper) based on morphology and genetics. We also document larval size and development and examine monthly vertical distributions and sympatric invertebrate taxa. We captured 1,048 pelagic larval Prickly Sculpin from 4.21 to 42.0 mm total length. Sampling occurred in traps set up to 20 m above the substrate, with Prickly Sculpin captured at all sampled depths. Captures shifted toward deeper reservoir habitats corresponding to increases in average body sizes as the season progressed from early spring to fall. We found most larval Prickly Sculpin at locations within the main reservoir body, several kilometers downstream of riverine areas. In addition to trap location, the abundance of larval Prickly Sculpin per trap was strongly associated with aquatic mites (absent from Prickly Sculpin stomachs). These findings suggest potentially shared ecological drivers of the observed distributions of larval Prickly Sculpin and mites. Collectively, we demonstrate that light trapping can be a useful method for collecting pelagic juvenile sculpins from reservoirs, in this case Prickly Sculpin, with the potential to improve our understanding of distribution, life-history patterns, and ecology throughout their range.