Size-dependent vulnerability of juvenile bay anchovy Anchoa mitchilli to bluefish predation: Does large body size always provide a refuge?

Abstract

Bay anchovy are known to be an important component of food webs in estuarine and coastal waters along the US east coast. Despite their role as a primary forage species for several top-level predators in these systems, very little is known about their behavioral interactions with predators and the vulnerability of post-larval life stages to predation. In this study, we examined the vulnerability of juvenile bay anchovy to age-0 bluefish predation using a size-structured laboratory design. For a range of bay anchovy and bluefish body sizes, we determined predator capture success, handling time costs, feeding rates, and prey profitabilities as functions of relative prey size. We evaluated bluefish size selection when offered different sizes of bay anchovy simultaneously and identified behavioral characteristics of prey that may contribute to disparate rates of attack. Bluefish capture success was high on small relative prey sizes (< 30% of predator size) and remained high on larger relative prey sizes (> 50% of predator size), demonstrating that even large bay anchovy are highly susceptible to capture. Handling time and capture success relationships were combined with prey body mass to generate dome-shaped profitability curves that peaked at relative prey sizes of 0.50, which is much higher than typically observed for piscivore-prey interactions. Bluefish exhibited strong selection patterns and significantly higher attack rates on large bay anchovy. Disparate attack distributions on large and small bay anchovy appeared to be caused partly by differences in prey behavior among size groups. Our results suggest that bay anchovy may not achieve a refuge from predation with increased body size and support the importance of predation in shaping bay anchovy life history.