Nocturnal Inshore Movement of the Mimic Shiner (Notropis volucellus): a Possible Predator Avoidance Behavior

Diel seining documented a significant summer nocturnal inshore movement of the mimic shiner (Notropis volucellus) in Lake Itasca, Minnesota. This species initiated inshore movement at sunset, occupied the nearshore area throughout the night, and moved offshore by sunrise. Mimic shiners were collected in less than 1 m of water throughout inshore areas with sparsely developed macroscopic vegetation. Greatest relative abundance was observed at sites possessing the greatest expanse of sparsely or nonvegetated substrate. Relative abundance at inshore sites may be related to habitat characteristics of the sites or to the proximity of feeding habitat. These diel movements differed markedly from those exhibited by the mimic shiner in other lakes. The inshore movement in Lake Itasca may function to reduce crepuscular and nocturnal predation pressure. Our data support the hypothesis that freshwater fishes may possess behavioral plasticity sufficient to alter movement and distribution patterns according to prevailing conditions and that predation pressure may be important in altering prey behavioral patterns.