Growth,production, food consumption,and mortality of juvenile spot and croaker: A comparison of tidal and nontidal nursery areas

As the dominant juvenile finfish in southeast and Gulf of Mexico nursery areas, spot and croaker growth, food consumption, production, and mortality are compared in tidal salt marshes and nontidal brackish systems. Growth rates of spot and croaker from 5 studies ranged from 0.021–0.04 g per g per d. Differences in the annual production and food consumption estimates were primarily due to differences in average biomass. Although mean biomass varied widely, the daily production to mean biomass ratios ranged from 0.021–0.037, suggesting that these systems probably could support more juvenile fish than are present. Spot mortality ranged from 0.023–0.041% per d. Despite large hydrographic differences between tidal and nontidal systems and large differences in the amount of detrital input, the secondary production values and many of the fish population parameters are remarkably similar. This is interpreted as confirmation of the basic trophic similarity of the different systems and the highly adaptable and general nature of juvenile fish. The primary consumers are supported by 50–100% of the algal production. But because the dominant fishes consume only 10–35% of that secondary production, at least in some systems, food does not appear to limit juvenile fish production. Predation on the juveniles is implicated as a limiting factor.