The surface accumulation of larval fishes by hydrodynamic convergence within the Mississippi River plume front

Abstract

In September 1987 and May 1988 densities of larval fishes at the surface were greater within the frontal zone of the Mississippi River plume than they were in plume or shelf waters. Sharp turbidity discontinuities of 10–50 m width accompanied by temperature and salinity discontinuities were embedded within this large-scale frontal zone, which itself spanned 2–20 km. Apparent convergent motion normal to turbidity discontinuities had velocities in the range of 0-0.8 m s⁻¹: lateral shear was also evident. Exceptionally high densities of larval fishes were not always observed at turbidity discontinuities. Turbidity discontinuities, often sinuous in configuration, formed and dissipated over time scales of 2–6 h. Expected densities of larval fishes within frontal convergence zones, calculated with a simplified advection-diffusion model, approximated mean and median densities observed within the large-scale frontal zone.