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. lo-0.30 m s-l, but this index does not explain variation in the accumulation of larval fishes. Frontal convergence may be localized and affected by secondary circulations.Planktonic organisms are typically aggregated in the vertical and horizontal dimensions on a variety of temporal and spatial scales. This aggregation is influenced by biological characteristics of these organisms and by physical fc:atures of their habitat (Haury et al. 1978; Longhurst 198 1; Owen 198 1;Mackas et al. 1985). The propagation of plankters, their behavior, and their buoyancy interact with the physical hydrographic structure and hydrodynamic motion of the ocean to affect aggregation. Propagation contributes to aggregation on most temporal and spatial scales; e.g. the cell division of phytoplankters, the reproduction of zooplankters, and the spawning of fishes produce aggregates of propagules over various scales that depend on the taxa. Interaction of buoyancy and behavior of plankters with hydrographic structure is effective more often in shaping spatial distribution at miAcknowledgments We acknowledge and appreciate the cooperation of S. Cummings for MOCNESS operations, the officers of the Oregon II for their navigation in the cluttered and busy waters of the northern Gulf of Mexico, and a squad of technicians for plankton sorting. J. M. Brubaker offered valuable counsel on the hydrodynamics of frontal convergence. P. B. Ortner reviewed the manuscript.T. Leming supplied the satellite images.

Spatial distribution and abundance of larval and juvenile fish, chlorophyll and macrozooplankton around the Mississippi River discharge plume, and the role of the plume in fish recruitment

“…On average, catches were over 6 times higher in frontal than in plume waters, the next highest. These findings are consistent with Govoni et al (1989) who found that larval fish densities were greater in surface waters at the turbidity front than on either side of it. Although we did not determine the vertical distribution of ichthyoplankton, we do not believe that the interaction of vertical distribution and plume effects influenced the observed spatial patterns of catch per tow, or the taxonomic composition.…”

“…Although we did not determine the vertical distribution of ichthyoplankton, we do not believe that the interaction of vertical distribution and plume effects influenced the observed spatial patterns of catch per tow, or the taxonomic composition. In addition, Govoni et al (1989) reported that the plume did not affect vertical distribution of larval fishes collected with a multiple opening/ closing net and environmental sensing system (MOC-NESS) in any way that resulted in a consistent pattern. Hydrodynamic convergence associated with frontal waters is a local, but powerful, transport mechanism that could aggregate ichthyoplankton (Govoni et al 1989).…”

“…In addition, Govoni et al (1989) reported that the plume did not affect vertical distribution of larval fishes collected with a multiple opening/ closing net and environmental sensing system (MOC-NESS) in any way that resulted in a consistent pattern. Hydrodynamic convergence associated with frontal waters is a local, but powerful, transport mechanism that could aggregate ichthyoplankton (Govoni et al 1989). As surface waters converge, driven by horizontal density gradients (and apparently additional factors like tide, wind and river flow), planktonic organisms move with converging water toward the front, where the converging water masses move downward due to gravitational pull on water on either side of the front.…”

“…El Nino) and perturbations in major current systems (e.g. the California Current; Lasker 1978) to smaller-scale phenomena such as wind events and resulting transport (Nelson et al 1977, Checkley et al 1988; storm-and upwelling-related turbulence (Lasker 1980); fronts, gyres, horizontal microstructure and eddy systems (Grainger 1978, Owen 1981a, Iles & Sinclair 1982, Hunter & Sharp 1983, Kirobe et al 1986, Richardson et al 1986); and riverine plumes, fronts and associated hydrodynamic convergence (Richardson 1981, Sakamoto & Tanaka 1986, Govoni et al 1989.…”

Fish Resources of the Gulf of Mexico

“…Combined, these factors result in large spatiotemporal variability in physicochemical conditions, causing primary production to vary markedly within and across areas of different oceanographic conditions in the Gulf of Mexico (Grimes and Finucane 1991;Biggs 1992). Physical-chemical variability affects the distribution, growth, and mortality of pelagic larvae of many fish species in the Gulf of Mexico (Govoni et al 1989;DeVries et al 1990;Lang et al 1994). Higher abundance, increased growth, and reduced mortality have been observed for larvae within frontal features created by riverine discharge and hydrodynamic convergence (Lang et al 1994;Hoffmayer et al 2007).…”