Covariation in feeding success, size-at-age and growth in larval radiated shanny (Ulvaria subbifurcata): insights based on individuals

Many studies infer that large size-at-age and/or fast growth rate confer a survival advantage to individual fish larvae by decreasing the time spent in the vulnerable larval stages. An implicit but generally unstated assumption is that one reason why some individuals grow faster than others is that they are better swimmers and, thus, more adept at catching prey and avoiding predators. Here we provide a direct test of the link between foraging success, length-at-age and growth history by examining the effect of size-at-age and growth rate (via otolith microstructure) on individual foraging success of radiated shanny (Ulvaria subbifurcata) larvae from coastal Newfoundland. Larvae that were large-at-age were more likely to have a larger volume of prey in their stomachs than were individuals that were small-at-age. Similarly, individuals with faster growth rates were also more likely to have more food in their stomachs than were those with slower growth rates, although this effect was both age-dependent and not as pronounced as the size-at-age effect. In terms of larval diets, because neither the mean nor the SD of prey-size in stomachs was correlated with length-at-age, it appears that individuals that were large-at-age did not prey on either larger or more diverse prey sizes than did individuals that were small-at-age. Interestingly, however, the mean prey size in stomachs was positively correlated with growth rate, suggesting a possible role for acquired behaviour or experience in patterns of prey selection by radiated shanny larvae.