Intraguild predation between spawning smallmouth bass (Micropterus dolomieu) and nest‐raiding crayfish (Orconectes rusticus): implications for bass nesting success

Abstract

Summary Predation on eggs is often assumed to be a primary factor influencing the reproductive success of fish. However, complex interactions between nesting fish and their egg predators may influence reproductive success in unexpected ways. The invasive rusty crayfish (Orconectes rusticus) and smallmouth bass (Micropterus dolomieu) engage in reciprocal predation during the bass spawning season; the net impact on bass reproduction is poorly understood. We hypothesise that the rates of nest abandonment and bass guarding behaviour will be positively related to crayfish abundance and that bass consumption of crayfish will mitigate energy loss due to nest guarding against crayfish. We tracked 62 bass nests throughout a spawning season in a north temperate lake with an established population of O. rusticus. Using video surveillance, we observed bass nest‐guarding behaviour and crayfish predation on bass nests, reconstructed bass diets using faecal remains and made repeated measurements of mass and length for a subset of the parental bass. Results were consistent with all hypotheses. Nest abandonment rate and guarding activity were higher in areas with higher crayfish density. More than 95% of bass consumed crayfish while on the nest and bass condition factor increased during nesting, suggesting that energy consumed exceeded energy expended in defending the nest. The lakewide rate of smallmouth bass nest abandonment was 13%, which is lower than most published observations for this species. While high densities of nest‐raiding crayfish can reduce nesting success, our limited observations indicate that consumption of crayfish may mitigate rates of nest abandonment by bass. Unexpected outcomes of complex interactions, such as reciprocal predation, should be considered when predicting population trajectories of native and invasive species.