FISHERY BULLETIN: VOL. 74, NO. 4 



Ponomareva (1963). The abundance in subsurface 

 waters and the possible migratory behavior of this 

 unspined form have not been documented 

 previously. 



Nematoscelis 



Two species of Nematoscelis were taken-A'^. 

 tenella and A^. difficilis. Nematoscelis tenella was 

 collected at only one day-night station (SOE 16). 

 The few adults and juveniles caught, 2-13/1,000 

 m', were found between 400 and 500 m during the 

 day and and 250 m at night. Nematoscelis 

 difficilis occurred between the surface and 450 m 

 at all but one station (SOE 25). This species was 

 more abundant near the coast along the CalCOFI 

 transect. Densities ranging in the hundreds per 

 1,000 m' at nearshore stations were an order of 

 magnitude larger than concentrations among 

 samples from waters farther offshore. Larvae and 

 most juveniles were taken only in the upper 100 m. 

 Adults were more abundant between 100 and 300 

 m, particularly at night. 



Stylocheiron 



Five species of this genus were found-S. affine, 

 S. longicorne, S. maximum, S. elegatum, and S. 

 abbreviatum. These species occupied similar depth 

 intervals day and night although each species 

 tended to inhabit a separate portion of the water 

 column. Stylocheiron affine occurred only along the 

 southern transect. All stages were collected 

 between 40 and 135 m and primarily at the most 

 offshore stations where densities of 60-150/1,000 

 m^ were recorded (SOE 25; CalCOFI 50.140). Each 

 stage was often more abundant in the night 

 samples. Stylocheiron longicorne, the most abun- 

 dant species of this genus, ranged between 70 and 

 350 m, but the bulk of the populations were within 

 the 150- to 250-m interval (Figure 4c). More 

 specimens were usually caught at night. Stylo- 

 cheiron maximum occurred in low densities at 

 every station, i.e., 5-40/1,000 m^. Larvae and 

 juveniles of this species were found most often 

 between 70 and 200 m. Adults were generally 

 deeper, ranging from 200 to 400 m. Differences 

 between day and night distributions indicate that 

 this species migrated less than 100 m, if at all. 

 Very small densities of S. elongatum, 1-27/1,000 

 m^, were observed at the offshore stations between 

 200 and 600 m. A few adults of S. abbreviatum 

 were found along the southern transect of the SOE 



932 



cruise. Four individuals were collected in the upper 

 150 m at stations well offshore (SOE 25, 39) and one 

 between 300 and 400 m nearshore (SOE 9). 



Nematob rachion 



Two species of Nemafobrachion were found— A'^. 

 boopis and N.Jlexipes. One to two individuals of A^. 

 boopis, mostly juveniles, were taken between 300 

 and 500 m and only during the day at a few, 

 southern stations (SOE 9; CalCOFI 70.75, 50.140). 

 Nemafobrachion fiexipes occurred at all but one 

 station (SOE 68). Small concentrations, usually 

 1-30/1,000 m-^ but ranging up to 69/1,000 m'', were 

 found regardless of the time of day. Juveniles 

 were often the most numerous stage. This species 

 was frequently encountered at 200-500 m during 

 the day. At night specimens were collected from 

 450 m to the surface with most of a population in 

 the upper 150 m. 



PATTERNS OF ABUNDANCE, 



VERTICAL DISTRIBUTION, 



AND DIEL MIGRATION 



The abundance and vertical distribution of the 

 more numerous euphausiid species in the upper 

 500-700 m differed in relation to distance from 

 shore, longitudinal position in the area sampled, 

 and vertical ranges occupied during a given day. 

 The largest densities of euphausiids occurred near 

 the coast (Table 2). Among the nearshore stations 

 (ca. 100-150 km from the coast) E. pacifica was the 

 numerically dominant euphausiid day and night, 

 composing 75-90% of all species observed. At 

 intermediate distances from the coast (ca. 300 km), 

 E. pacifica was less abundant, making up 36-60% 

 of the species collected, but still ranked first except 

 in the north (SOE 74) where Thysanoessa longipes 

 formed 69% of the day catch. Other euphausiid 

 species constituting 15-30% of the total number 

 included S. longicorne, E. gibboides, T. gregaria, 

 and T. longipes. At stations farthest offshore (ca. 

 600-700 km) along the southern transects, T. 

 gregaria and S. longicorne were the most abun- 

 dant species, forming 75% of the total during the 

 day. At night, larger numbers of E. gibboides, E. 

 mutica, and E. reciirva were collected such that 

 these populations also ranked among 75% of the 

 euphausiids collected. To the north, T. longipes and 

 S. longicorne were the abundant species, compos- 

 ing 70-80% of all euphausiids. These changes in 

 species composition and dominance represent the 



