Evaluating the effects of marine reserves on diet, prey availability and prey selection by juvenile predatory fishes

Implementation of effective no-take marine reserves almost universally results in an increase in the abundance of adult stages of exploited predatory fishes. However, the effects of reserves on the ecology of the juvenile stages of predators are unknown. Increased predation pressure from adults in reserves may not only reduce juvenile recruitment directly, but as a result of non-consumptive effects, may impact on critical aspects of their foraging behaviour, including diet and prey selection. In general, the feeding ecology of juvenile stages of large predators is poorly understood due to their relatively low abundance and cryptic behaviour. Here, we examined differences between reserves and fished areas in recruit abundance, diet, prey availability, and prey selection indices for recruits and juveniles of 3 predatory fishes: Plectropomus maculatus, Lutjanus carponotatus and Epinephelus quoyanus. Recruit abundance was similar between reserves and open areas. The diets of the 3 study species did not differ between reserves and open areas, with variation in diets largely explained by fish species and body size. At small sizes, all species consumed high numbers of shrimp, but diets diverged with growth. Overall, our results provide little evidence that more abundant predators inside reserves influence juvenile feeding ecology.