Experimental Test of Preference by a Predatory Fish for Prey at Different Densities

Preference for a particular prey implies that a behavioral choice is made by the predator, requiring an experimental approach to separate process from observed patterns in nature. For example, pink shrimp (Farfantepenaeus duorarum) and pinfish (Lagodon rhomboides) are dominant prey observed in the diet of juvenile gag (Mycteroperca microlepis) collected from natural habitats, but it is unclear whether their approximate equal representation is due to a lack of preference between the two. Furthermore, both prey are captured in high quantities as targeted (shrimp) and non-targeted (pinfish) components of a trawl fishery operating in the same seagrass habitats where juvenile gag are found, thus requiring examination as to whether reductions in prey densities affect consumption rates and preference. In the current study, I used laboratory feeding experiments and applied new analytical techniques derived in a series of recent papers published in this journal to examine preference by juvenile gag on these two morphologically and behaviorally different prey. Consumption rates were higher for shrimp than pinfish and were not related to the initial density of prey presented to gag. However, gag did not exhibit a feeding preference for either prey across 10 controlled comparisons. Experimental results in the laboratory therefore reflected patterns observed in the field for the diet of this predatory fish. Moreover, by examining the effects of reduced prey densities on food web processes, the approach used in this study may be applied to inform ecosystem-based management on indirect effects of fishing