Survival skills required for predator evasion by fish larvae and their relation to laboratory measures of performance

Our objective was to determine which survival skills were most informative of larval fish's escape potential, and thereby better understand larval fish strategies for predator evasion and the nature of selective pressures during early life. We examined evasive performance of red drum larvae, Sciaenops ocellatus, in predation trials and related their escape potential to 12 putative survival skills measured in nonlethal assays. The putative survival skills measured were spontaneous swimming speed and the responsiveness, timing and magnitude of escape responses elicited by artificial stimuli. Responsiveness to the predator was the primary determinant of success in predation trials, accounting for 86% of the variation in escape potential. Of 12 putative survival skills and composite variables that summarized all putative skills, only visual responsiveness (proportion of stimulus presentations responded to) was significantly correlated with escape potential. Regression tree analysis showed that three putative survival skills could be applied in sequence to coarsely filter larvae according to escape potential. Previous work showed that batches of larvae (spawns) could be grouped into clusters whose members showed similar levels of performance in most putative skills. Predation trials showed that escape potential varied as predicted by these clusters. Our results imply that some putative survival skills measured in nonlethal assays reflect responsiveness to an actual predator, but they do not relate directly to their analogues in actual predator–prey interactions. Nevertheless, the ability to distinguish unlikely survivors from more fit individuals, even coarsely, can be valuable for designing experiments, and careful interpretation of putative survival skills can improve ecological models designed to project the fate of larval cohorts.