Document: JAM-3-80-2

Density-dependent growth and survival of juvenile spot, an estuarine-dependent fish.

RICE, J.A.* ¹ and L.B.CROWDER ²

North Carolina State University Raleigh NC 27695 USA ¹
Beaufort NC 28516 USA ²

Abstract:
While many organisms exhibit density-dependent growth and/or survival, some ecologists have hypothesized that the density of juvenile estuarine-dependent fishes is constrained by the number of larvae transported to nursery areas, and typically remains below carrying capacity, preventing food limitation and density-dependent effects. This question has gained additional significance as hypoxic conditions due to excessive nutrient loading substantially reduce the amount of available habitat. We conducted two experiments to test for density-dependent growth and survival of juvenile spot Leiostomus xanthurus. In the first experiment fish were placed in 1-m² cages in an estuarine marsh creek at densities of 0, 2, 5, and 10 fish/m² (6 replicates each) and their growth and survival were determined after 51 d. In the second experiment spot were stocked in 79-m² pond sections at densities of 0, 2, 5 and 10/m² (2 replicates each) and their growth and survival were determined after 52 d. Benthic core samples were also taken to assess the effects of spot densities on infaunal prey. In both experiments spot growth and survival were significantly reduced as fish density increased. Growth rate increased 5 to 30-fold as spot density declined from 10 to 2 fish/m², and P (mortality) increased 2 to 5-fold with increasing spot density. At the end of the pond experiment, densities of benthic meiofauna commonly fed upon by spot declined significantly with increasing spot density. Estimates of spot density gleaned from the literature indicate that these density-dependent effects occur well within the range of realistic field densities. These results suggest that hypoxic events may have substantial indirect effects on fish populations as habitat reductions (often 30-50%) result in increased densities in remaining habitat.

Keywords: density-dependent growth, density-dependent survival, leiostomus xanthurus, hypoxia

This abstract is being presented at: 8:45 AM in session:
Oral Session #57: Ocean-Going Fish and Mammals.