ON THE STRUCTURE OF A DEEP SCATTERING LAYER ON THE COASTAL SHELF OFF BAHIA-MAGDALENA, BAJA-CALIFORNIA, MEXICO

The structure of an intense deep scattering layer off the southwest co ast of Baja California, Mexico, is described using Isaacs-Kidd net tra wl samples, Bongo samples and hydroacoustic records. Results demonstra te the dominance of three organisms: an euphausiid, Euphausia eximia H ansen 1911, a decapod of the family Galatheidae, Pleuroncodes planipes (Stimpson, 1860); and a fish of the family Photichthyidae, Vinciguerr ia lucetia (Carman, 1899). Using a SIMRAD EY-200 echosounder, with a w orking frequency of 200 kWz, and a Hydro Acoustic Data Acquisition Sys tem (HADAS), echoes were separated according to their target strength. Euphausiids were associated with the -56 to -62 dB target strength gr oup, the red crabs with the -51 to -55 dB group, and fishes with the - 32 to -50 dB group. Results indicate that organisms within the layer w ere not randomly distributed, but that they have an internal structure both in a horizontal and vertical dimension.