The influence of behavior on size-structured predator -prey interactions: Prey susceptibility, predator selection, and population-level consequences for juvenile estuarine fishes
This dissertation examines the influence of predator and prey behavior on the outcome of size-structured species interactions between piscivorous fishes and their prey. A primary focus was to evaluate the relative susceptibility of bay anchovy to predation and identify potential mechanisms responsible for differences among bay anchovy and other common forage species.
Bay anchovy were highly susceptible to capture by bluefish and required minimal handling time. Bay anchovy greater than 40% of bluefish body size were highly profitable prey, which is not typical for most piscivore-prey interactions. Bluefish selected large bay anchovy when given a choice of prey sizes. High attack proportions on larger bay anchovy may have been influenced by size-related differences in antipredator behaviors. Results indicate that bay anchovy probably never achieve a size refuge from predation.
Compared to other common forage species, bay anchovy were the easiest prey to capture, required low handling times, and were generally the most profitable prey for piscivores. Short reaction distances to approaching predators may have contributed to disparate susceptibilities to capture among forage species. Findings highlight the potential importance of life history strategy and phylogeny in determining the effectiveness of the antipredator behaviors expressed by prey.
Piscivores consistently selected bay anchovy over several alternative forage species. Attack proportions were highly skewed toward bay anchovy prey. Forage species differed considerably in the expression of antipredator behaviors related to use of refuge, tank positioning, activity levels, schooling aggregation, and the frequency of stragglers. Piscivores displayed several attack strategies, but mostly attacked solitary prey individuals. Differences in antipredator behavior appeared to directly influence predator attacks, suggesting that differential attack proportions among prey may not necessarily represent active choice by piscivores.
Piscivores differed in their patterns of resource utilization, with bluefish achieving piscivory earlier and consuming larger prey sizes compared to striped bass. Behavioral foraging abilities differed markedly between piscivores, with bluefish foraging efficiency reaching levels nearly four times those reached by striped bass. When prey resources were limited, bluefish grew faster than expected and were able to exploit prey at the expense of striped bass. Findings indicate the importance of available forage fish of appropriate size to the onset of piscivory in striped bass.
0792: Fish production