Effects of temperature and prey size on predator-prey interactions between bluefish and bay anchovy

Little is known about the behavioral responses of fishes at low temperatures. Of particular interest are predator-prey interactions because feeding at low temperature is necessary for the overwinter survival of many species. This experiment examined how low temperatures affect behavioral interactions between bluefish (Pomatomus saltatrix L.) and two sizes of bay anchovy (Anchoa mitchilli V.) prey. Temperature had an effect on multiple responses of predator-prey encounters including the approach distance of bluefish towards prey, attack and escape speeds, and prey handling time. The reaction distance of prey was important in determining the outcome of an attack; anchovy reacting at a greater distance from an attacking bluefish escaped more often. However, temperature did not have an effect on either reaction distance or bluefish capture success. The influence of prey size depended on how capture success was defined. Bluefish ability at catching prey was not affected by anchovy size, but larger prey were ingested less frequently due to a greater incidence of prey being dropped in trials with large anchovy. Further, bluefish had greater difficulty handling and ingesting prey at lower temperatures, especially for larger prey. At the lowest temperature treatment small anchovy were readily consumed, but no attacks were made on larger prey. This shows that bluefish modify prey size-selectivity behavior based on temperature, which probably results from a perceived inability to handle and ingest large prey at low temperatures. These results suggest that at low winter temperatures bluefish are restricted to smaller prey.