Diet Diversity of Two Sculpin Species (Cottidae) in Midwestern USA Trout Streams: Patterns Across Nine Years After Severe Summer Flooding

Abstract

The geographic ranges of slimy (Uranidea cognata) and mottled (Uranidea bairdii) sculpin overlap broadly across cool and coldwater streams and rivers in North America, where they can serve very important roles in fish community dynamics. The diet diversities of slimy and mottled sculpin were examined in early March (late winter) during eight out of nine years after the August 2007 catastrophic flooding in four streams to assess potential diet shifts as benthic invertebrate prey communities recovered post-flood. In total, 10,823 prey items, representing 39 invertebrate taxa and three fish taxa were identified from the stomachs of 532 slimy sculpins (present in Garvin Brook, Gilmore Creek, and Trout Run) and 179 mottled sculpins (present in Middle Fork Whitewater River). Only four prey taxa were consumed by sculpin in all streams: midge larvae and pupae (Diptera: Chironomidae), blackfly larvae and pupae (Diptera: Simuliidae), Hydropsyche caddisfly larvae (Trichoptera: Hydropsychidae), and Baetis mayfly nymphs (Ephemeroptera: Baetidae). Midges dominated diets of both slimy (61% of prey by number) and mottled (76%) sculpin across all years. Consequently, Shannon diversities of diets were typically low across all years and streams for slimy sculpin (annual site range 0.07–0.83) and across years for mottled sculpin (annual range 0.11–0.46). Diversities and taxa richness of slimy sculpin diets increased in Garvin Brook and Trout Run across the study years (driven by significant declines in midge dominance) but remained relatively unchanged for slimy sculpin in Gilmore Creek and mottled sculpin in the Middle Fork. Individual slimy and mottled sculpin differed significantly both in the numbers of taxa consumed per fish (<2 versus 2.5 taxa/fish, respectively) and in the numbers of individual prey per fish (11 versus 26 prey, respectively). Slimy sculpin in two streams displayed modest shifts in diets as benthic prey communities recovered during the 9-year period post-flood, whereas slimy and mottled sculpin in other streams displayed little to no changes in diets. Differing flood severity among streams may have produced the different responses observed in sculpin diets.

Keywords

• slimy sculpin
• mottled sculpin
• diets
• diversity
• flooding