Comparison of multipiscivore foraging success on native and invasive prey fish under variable light intensities.
Piscivorous fishes attack and consume a variety of prey; however, few studies have examined interactions of multiple predators with multiple prey species. The situational complexity of foraging at different times of day was explored by examining the interactions of paired native predators (Burbot Lota lota or Smallmouth Bass Micropterus dolomieu) with either native (Mottled Sculpin Cottus bairdii) or invasive (Round Goby Neogobius melanostomus) benthic prey. The study allowed the comparison of a pursuit predator (Smallmouth Bass) and an ambush predator (Burbot). Trials were performed under natural relevant lighting conditions with downwelling light intensity and emission spectrum matched to the irradiance at a 10-m depth in the St. Louis River estuary during the summer at night, civil twilight, sunrise, and midmorning. Smallmouth Bass were more active and initiated 1,510 reactions that resulted in the successful capture of 61 Round Goby and 103 Mottled Sculpin, whereas Burbot initiated 475 reactions resulting in 24 successful retentions, including 9 Round Goby and 15 Mottled Sculpin. The percentage of successful retentions was greater for Smallmouth Bass (10.9%) than for Burbot (5%). Reaction probabilities to each prey differed significantly, which resulted in a two-fold increase in attacks on Mottled Sculpin compared with Round Goby within the same time period. Reaction distances for both predators did not differ regarding prey species, but Smallmouth Bass reacted from farther away than did Burbot (maximum reaction distances of 159 and 98 cm, respectively). Greater success of native predators on native prey has likely caused higher mortality on native prey populations due to greater predator success, while capturing invasive prey decreases the net energy intake.