Lavaniegos Vertical distribution of euphausiid life stages 



301 



been reported by Fleminger (in 

 Brinton et al., 1986). Point Eugenia 

 is of biogeographical interest because 

 species of temperate, tropical, and 

 central Pacific regions may occur to- 

 gether relatively near to the coast 

 (Boden et al., 1955; Brinton 1962, 

 a and b). 



Methods 



Samples used in this study were col- 

 lected from a three-station transect 

 off Point Eugenia, Pacific coast of 

 Baja California (Zigpac II cruise, 12- 

 18 June 1961), and from three sta- 

 tions from the central part of the Gulf 

 of California (El Golfo II cruise, 15- 

 20 May 1965 ) ( Fig. 1 ). In both cruises 

 of RV Alexander Agassiz, two series 

 of tows (one during the day and one 

 at night) were made with an open- 

 ing-closing net as described by 

 Brinton (1967). The net was 1 m in 

 diameter, 2.35 m long, and used 0.505-mm mesh with 

 0.25-mm mesh in the codend bag as well as a 40-cm 

 long section at the front of it. Off Point Eugenia, nets 

 were hauled horizontally at discrete depths (0, 10, 

 25, 50, 75, 100, 150, 200, 300, 400, and 500 m) for 30 

 min. In the Gulf of California, hauls were oblique 

 and nets equipped with flowmeters. In the upper 150 

 m, five hauls were made through strata of 30 m; be- 

 low 150 m, five hauls were made through strata of 

 135 m. 



Euphausiids were identified, counted, and grouped 

 as adults (males and females), juveniles, and larvae. 

 The entire sample was used except in cases of abun- 

 dant Nyetiphanes simplex and Euphausia recurva, 

 where subsamples were obtained with a Folsom split- 

 ter. Between 200 and 400 individuals per life phase 

 were typically counted. Larvae of Nematoscelis 

 difficilis and N. simplex were sorted by developmen- 

 tal stages as defined by Gopalakrishnan ( 1973) and 

 Lavaniegos (1992). The biogeographic provinces of 

 Brinton (1962a, 1979), based on affinity to water 

 masses, were used in the classification of species. 



Abundance at a particular depth is expressed as 

 individuals (ind)/m 3 , and total abundance in the 

 water column as ind/m 2 of ocean surface. In horizon- 

 tal hauls, the depth of tow was taken as the middle 

 depth of the layer. In oblique hauls, the thickness of 

 the layer was the difference between depths of open- 

 ing and closing of net. Statistical comparisons were 

 not made because of absence of replicate tows. Data 



Figure 1 



Sampling stations (•) off Point Eugenia, Pacific Coast of Baja California. 

 Isobaths are in fathoms. 



on temperature, salinity, and dissolved oxygen were 

 obtained from standard Nansen-bottle casts and pro- 

 cessed by California Cooperative Oceanic Fisheries 

 Investigations. Data from the Gulf of California are 

 published (SIO Data Report 1 ). 



Results 



Hydrographic vertical profiles 



In the outer coast of Baja California, physical condi- 

 tions in June 1961 were typical for late spring (Reid 

 et al., 1958; Hickey, 1979; Huyer, 1983). Near the 

 coast (station [st.] 120.45), the mixed layer was 20 m 

 (Fig. 2). The station most distant from the coast (st. 

 120.60) showed a thicker mixed layer (50-60 m) and 

 warmer temperatures between depths of 20-150 m 

 than did the other stations. Salinity in the surface 

 layer showed low values (33.5-33.8 ppt), influenced 

 by more northern California Current water. Near the 

 coast (st. 120.45), a shallow oxycline and values of 

 salinity >34.0 ppt at 75-100 m depth resulted from 

 the influence of Intermediate Equatorial water. 



The Gulf of California is influenced by northerly 

 winds during spring and summer. However, tides. 



1 SIO Data Report. 1967. Physical and chemical data report: 

 CalCOFI Cruise 6505 (El Golfo II). SIO Reference 67-16. 

 Scripps Institution of Oceanography, La Jolla, CA, 92093. 



