FISHERY BULLETIN: VOL. 76, NO. 4 



and descent of the migratory sound-scattering 

 layer depended on weather conditions; also, year- 

 to-year differences are attributed to slight varia- 

 tions in time of cruises. We usually set the lower 

 limit of nekton sampling at least 50 m below the 

 depth of the deep nonmigratory scattering layer. 

 With the exceptions noted below, nighttime sam- 

 pling was confined to the time period between as- 

 cent and descent of the migratory scattering layer. 



Somewhat different sampling programs were 

 carried out in different years (Table 1 ). At Station 

 P in 1973 the objective was to obtain information 

 on vertical distributions offish and zooplankton to 

 aid in developing an optimal sampling strategy for 

 studying diet and feeding behavior of myctophids. 

 The 0-440 m water column was sampled in 55-m 

 depth strata, and seven successive vertical series 

 of samples, 4 night and 3 day series, were 

 obtained. A shallow haul (0-220 m) and a deep 

 haul (220-440 m) were required for each complete 

 vertical series. The first nighttime series was not 

 completed before the descent of the migratory 

 sound-scattering layer. In order to obtain both the 

 shallow and deep hauls during one night, the 

 hauls were of relatively short duration, and con- 

 sequently the nekton samples were relatively 

 small. 



At Station Q in 1974, the objectives were to 

 confirm the vertical distributions found in 1973 at 

 Station P and to document the feeding chronology 

 of the common myctophids. The sampling for ver- 

 tical distributions ( Table 1 ) extended from the sur- 

 face to between 400 and 460 m, depending on the 

 depth of the deep sound-scattering layer, and usu- 

 ally included one sample collected below the scat- 



Table 1 . — Sampling data for vertical series of nekton samples in 

 the northeastern Pacific. The three lower entries for Station P 

 (1975) represent data for; first, the routine day-night vertical 

 series (0-400 m); second, a single shallow (0-60 m) night vertical 

 series; and, third, a single deep (440-782 m) daytime vertical 

 series. 



P 5-9 Aug. 



1973 7.2 = 0.5 29(16-45) 8.412 (4,863-13,357) 

 O 18-22 July 



1974 6.2±0.5 45(24-66) 14.229 (6,833-20,361) 

 P 26-28 July 



1975 6,9 = 0.5 32(19-43) 10.984 (7.664-14,731) 

 27 July 



1975 6.9=0.5 21 (16-29) 7.638 (6,184-10,052) 

 31 July 

 1975 6.9±0.5 68(58-79) 23,232 (20,012-28.614) 



tering layer. Complete daytime vertical series 

 (both shallow and deep hauls) of samples were 

 collected on 2 days; as no fish were collected in the 

 upper 200 m, two additional daytime vertical 

 series were made with only one haul extending 

 from below the depth of the sound-scattering layer 

 to about 200 m. In order to achieve adequate sam- 

 ple size, the duration of each haul was long, but 

 because there were so few hours of darkness, only 

 one nekton haul could be made each night. Data 

 from a shallow haul and a deep haul on successive 

 nights were therefore combined to give a single, 

 complete, night vertical series; two such night 

 series were obtained, and all sampling was per- 

 formed between ascent and descent of the migra- 

 tory sound-scattering layer. 



In addition to vertical series of nekton samples 

 taken at Station Q, we utilized two types of hori- 

 zontal hauls. To identify components closely as- 

 sociated with the migratory sound-scattering 

 layer, on two evenings the trawl was launched 

 near sunset and towed horizontally at 125 m. The 

 12-kHz echosounder was operated continuously 

 during the hauls. Approximately 30 min before 

 the scattering layer began to ascend from its day- 

 time depth, a trawl net was opened and sampling 

 began. The second net was opened just as the scat- 

 tering layer reached 125 m, and the net was closed 

 after the layer had passed that depth. The trawl 

 was towed at 125 m for an additional 30 min, 

 taking a third sample, then closed and retrieved. 

 As part of the study of diel variations in feeding 

 intensity of myctophids, a series of three horizon- 

 tal hauls, each yielding four samples of 30 min 

 duration, was made in the upper layer (40-m 

 depth) throughout one night. 



The sampling program at Station P in 1975 was 

 similar to that at Station Q, although the nekton 

 sampling for vertical distributions (Table 1) was 

 much less extensive than in the previous two 

 cruises. We obtained only one complete nighttime 

 vertical series (400-0 m) and two deep daytime 

 vertical series (385-220 m) to check on vertical 

 distributions of myctophids. We collected one shal- 

 low vertical series in the 0-60 m layer in 15-m 

 depth strata to examine the vertical distribution 

 of myctophids within the surface layer at night, 

 and we took one very deep daytime vertical series 

 (782-440 m) to determine the distribution of myc- 

 tophids below our usual sampling depths. 



All samples obtained with the nekton trawl 

 were preserved in a 47f formaldehyde seawater 

 solution buffered with sodium borate. 



754 



