The spatial distribution of larvalfishes about the Mississippi River plume

Abstract

The distribution of larval fishes is shaped by the Mississippi River plume at both coarse (kilometers) and fine (tens to hundreds of meters) spatial scales. Density estimates of larval fishes (No. m −3 ), based upon ichthyoplankton samples collected about the Mississippi River plume in February 1982, December 1982, and November 1983, were often greater by a factor of 10, and sometimes by several orders of magnitude, at the plume front than they were inside (within) or outside of the plume. Greater densities at the plume front were most apparent for larval Brevoortia patronus (a clupeid) and unidentified clupeid larvae. Frontal convergence apparently affects the accumulation of larval fishes at the frontal interface, but high densities were not evident everywhere along the front. An index of potential convergent velocity indicates maximal velocities of the order of 0.10–0.30 m s −1 , but this index does not explain variation in the accumulation of larval fishes. Frontal convergence may be localized and affected by secondary circulations.