Differential Prey Selectivity of Largemouth Bass Functional Feeding Groups in Twin Lakes, Washington

Abstract

Largemouth bass (Micropterus salmoides) can be top-down regulators in a fish community. It is important for fisheries biologists who manage predator-prey populations to understand when bass become piscivorous. We examined the stomach contents of 622 largemouth bass in watershield (Brasenia schreberi) beds in North and South Twin Lakes, Washington. Bass displayed temporal and ontogenetic diet variation within and between lakes. Bass <100 mm fed principally on zooplankton and scuds in June and September and on benthic invertebrates, especially midge and damselfly larvae, during July and August. Damselflies, midges and scuds were major diet constituents for bass 100–199 mm. Bass 200–299 mm consumed large numbers of macroinvertebrates but also fed on crawfish and golden shiner (Notemigonus crysoleucus). Overall, the importance of large prey items like golden shiners and crawfish increased while macroinvertebrate importance to bass diets decreased as the fish grew larger. Bass piscivory was focused on golden shiners and was only observed in larger fish >300 mm. Golden shiner consumption was the lowest during June and September when cannibalism, crawfish and trout consumption increased. Temporal and ontogenetic variability in bass diets is most likely due to habitat variability, fish size, and prey availability and size. Manipulation of bass piscivory through slot-length-limits and/or macrophyte removal could be examined as a potential method for controlling nuisance forage fish such as golden shiners.