The Pacific yellowleg shrimp, Farfantepenaeus californiensis, on the continental shelf and in adjacent lagoons: Is there a response to differences in depth?

This study describes the relationships of the body length and the population density of the yellowleg shrimp, Farfantepenaeus californiensis (Holmes, 1900) with differences in depth, in two coastal lagoons and on the adjacent continental shelf of the Gulf of California. The Agiabampo and Navachiste lagoon systems are located on the east side of the Gulf of California, bordering the states of Sonora and Sinaloa, Mexico. The environmental conditions of the lagoons are stable, with salinities of 35.5 to 38 psu over an annual cycle. Before sampling, the bathymetry of the lagoons was studied. From December 2001 to January 2003, sampling of shrimp was performed monthly for five consecutive days. The preference of shrimp for a particular depth, according to their size, was examined and the density of shrimp at selected depths was compared. Large differences in body size between the samples at selected depths were found. The density of the shrimp did not correspond with depth, but small shrimp showed greater mean densities. The cues used by species for offshore movement may largely be size-related. Juveniles moved down the estuary and out to sea as they grew. Depth may be involved in the migration of shrimp from lagoons with stable salinity gradients. Migration requires that the shrimp respond to some cue associated with size or to some change in their environment. The conclusion in this study is, that the yellowleg shrimp, F. californiensis responds to differences in depth, depending on its size, which is independent of whether it is inside the lagoon or in an open marine habitat.