VERTICAL-DISTRIBUTION OF EUPHAUSIID LIFE STAGES IN WATERS ADJACENT TOBAJA-CALIFORNIA

Vertical distribution of euphausiids on opposite sides of Baja Califor nia, off Point Eugenia to the west (June 1961) and in the central sect or of the Gulf of California to the east (May 1965), are described fro m day and night sets of samples. Off Point Eugenia, the thermocline wa s shallow (20 m) toward the coast, characteristic of upwelling in late spring. In the Gulf, the Salsipuedes Channel showed well-mixed water whereas the Guaymas Basin had a stratified profile of temperature and oxygen. Lower abundances of the larger euphausiids during day througho ut the water column, compared with night, are attributed to net avoida nce. When a thermocline was present, two basic migration patterns were observed: 1) species crossing the thermocline (Nyctiphanes simplex an d most Euphausia spp.) and 2) species remaining at or beneath the ther mocline (Euphausia gibboides and Nematoscelis difficilis). On the basi s of distribution at night, the youngest larvae and adults of N. simpl ex were in the mixed layer at the coastal station off Point Eugenia; m ore advanced stages of development were at mid-depth, between 0 and 50 m, suggesting an upwelling-downwelling cell of circulation. Inside th e Gulf, abundant metanauplii and ovigerous females of N. difficilis oc curred only in the upper layers of Salsipuedes Channel, whereas in Gua ymas Basin and Point Eugenia, the youngest larvae were within the ther mocline. The decrease of oxygen with depth did not reach the critical values observed in the more tropical eastern Pacific but, in general, where values of [O-2] were <1 mL/L, the abundance of euphausiids was l ow.