Effects of Size Structure on Trophic Interactions between Age‐0 Smallmouth Bass and Juvenile Anadromous Alewives

Abstract

AbstractAge‐0 alewives Alosa pseudoharengus may compete for food with age‐0 smallmouth bass Micropterus dolomieu, possibly resulting in declines to some smallmouth bass fisheries in the northeastern United States and Atlantic Canada. Such competition could dramatically influence the recruitment of smallmouth bass in this region because they are at their northern limit of distribution and age‐0 smallmouth bass must accumulate sufficient lipid reserves to survive the overwinter period. We examined the temporal patterns of diet and isotopes of carbon and nitrogen for age‐0 alewives and smallmouth bass in a natural lake and a reservoir where alewife escapement is managed. Multiple alewife spawnings occurred in the lake, and small‐bodied alewives were abundant throughout the summer. There was minimal diet overlap, age‐0 alewives became a significant component of the age‐0 smallmouth bass diet, and age‐0 bass grew larger in this system. In the reservoir, escapement of alewife spawners was truncated, and a single‐size age‐0 cohort was observed. Alewives were similar in size to age‐0 smallmouth bass, and by late summer their diets showed some overlap and δ13C and δ15N levels were similar. Both predation and the potential for competition existed for these species, and their interactions depended on body size relationships. This is an important consideration in alewife management strategies where coexisting fisheries for smallmouth bass are desired.