Ontogenetic microhabitat shifts in Sacramento pikeminnow, Ptychocheilus grandis: reducing intraspecific predation

Abstract

The Sacramento pikeminnow (Ptychocheilus grandis) is a piscivore that will prey on its own young in streams. Microhabitat use by two size classes of juvenile pikeminnow in stream pools with and without adults present was examined in the South Yuba River, California. Juvenile pikeminnow were generally found in shallower and slower conditions than adult pikeminnow, but shifted to even slower and shallower conditions with more cover in the presence of large adults. Microhabitats selected were related to fish size, suggesting that intraspecific predation was the dominant factor affecting local distribution. Patterns of microhabitat use were consistent with ecological segregation of species and size classes observed in other California streams with more diverse fish faunas.

Lateral and Longitudinal Displacement of Stream‐Rearing Juvenile Bull Trout in Response to Upstream Migration of Spawning Adults

“…display ontogenetic shifts in habitat use (Schlosser 1987;Grant and Brown 1998;Manderson et al 2004;Gard 2005). However, ontogenetic shifts are especially evident in diadromous fish, which have both marine and freshwater life stages, and adfluvial fish, which use both lotic and lentic systems at different life stages.…”

“…In lakes, small Rainbow Trout Oncorhynchus mykiss use the more energetically profitable pelagic zone when larger conspecifics are absent, whereas the small fish constrain their activity to shallow nearshore habitat when large conspecifics are present (Landry et al 1999;Biro et al 2003). Similarly, juvenile Sacramento Pikeminnow Ptychocheilus grandis in streams display shifts to shallower water when larger, cannibalistic conspecifics are present (Gard 2005). The use of habitat where larger predators are inefficient, such as shallow and marginal waters, suggests an attempt by small fish to avoid predators, thus reducing their risk of predation or cannibalism.…”

“…Vulnerability to predation by aquatic predators diminishes with increasing fish size or decreasing predator : prey size ratio (Schlosser 1988;Roussel and Bardonnet 1999;Englund and Krupa 2000) and may result in a graded response in habitat shifts to deeper water as fish grow (Mäki-Petäys et al 1997;Gard 2005). The gradual shift to deeper water by larger fish may also be in response to the emerging risk of predation from terrestrial or avian predators, which hunt more successfully in shallow water than in deep water (Power 1987;Englund and Krupa 2000).…”

“…The size-and depth-mediated partitioning of habitat hence decreases the overlap in habitat use, allowing small fish and large fish to coexist (Schlosser 1987;Harvey 1991;Landry et al 1999;Gard 2005). However, even with an effective shallow refuge, other factors (e.g., predator or prey abundance) have major impacts on the intensity of predator-prey interactions (Schlosser 1987;Brown and Brasher 1995).…”