YOUNGBLUTH: VERTICAL DISTRIBUTION OF EUPHAUSIIDS 



m. Depth intervals of about 100 m were sampled. A 

 single frame (CalCOFI) was employed at depths 

 from 600 to 800 m. The nets were hauled along a 

 single oblique path (all CalCOFI and shallow SOE 

 casts) or undulated obliquely through the depth 

 intervals sampled (all mid-water SOE casts). Each 

 point on the graphs representing these data is the 

 middepth of the water column sampled. 



The strata sampled were recorded with a 

 Benthos depth-time device attached a few meters 

 below the bottom frame. Vessel speed during the 

 tows ranged between 2 and 2.5 knots (3.7 and 4.6 

 km/h) and was regulated to maintain a wire angle 

 of approximately 50°. Mean volumes of 619 m-^ 

 (SOE shallow tows), 957 m'' (SOE mid-water 

 tows), and 546 m-^ (all CalCOFI tows) were filtered. 

 All data were standardized to a volume of 1,000 m^, 

 assuming 100% filtration efficiency. Clogging of 

 net apertures was observed only in the uppermost 

 nets at the nearshore stations on the CalCOFI 

 cruise. 



The samples were preserved in 5% Formalin- 

 solution buffered to pH 7.6. All organisms longer 

 than 2 cm were removed from the sample and wet 

 weights were determined after draining the 

 remaining portion on a 0.222-mm mesh screen and 

 blotting it on absorbent paper for 20 min. Du- 

 plicate estimates varied by an average of 6%. 



The larvae (furcilia), juveniles (postlarvae and 

 immatures), and adults (sexually mature) of all 

 euphausiid species were studied. All individuals of 

 the less abundant species were identified and 

 counted. The densities of the more numerous 

 species were determined from subsamples made 

 with a modified Folsom Plankton Splitter. The 

 average number of specimens examined in the 

 subsamples was about 300. Duplicate counts were 

 compared with each other by calculating a Percent 

 Similarity Index (Whittaker 1952). 



If the index indicated at least 80% agreement 

 between the first two replicates, no other counts 

 were made. Occasionally a third count was 

 necessary. 



The taxonomy of adult euphausiids follows 

 Boden et al. (1955). Identification of certain 

 difficult groups, e.g., Nematoscelis spp., Thysan- 

 oessa spp., and all larvae were verified by E. 

 Brinton, T. Antezana, and K. Gopalakrishnan at 

 the Scripps Institution of Oceanography. When 

 specimens lacked some of the usual key characters. 



general body form and eye size, shape, and color 

 were used to distinguish the species. 



RESULTS 



Sampling Variability Between Cruises 



Samples were collected along four transects. 

 The stations ranged from 130 to 693 km off the 

 coast (Figure 1). During the CalCOFI cruise, a 

 smaller average volume of water was filtered by 

 each net. Presumably this smaller volume could 

 have introduced some bias by reducing species 

 diversity and abundance estimates. Comparisons 

 of the results from each cruise indicate that, 

 except for three rarely caught species: 1) the 

 number of euphausiid species collected was iden- 

 tical and 2) the order of species abundances was 

 quite similar on each cruise. Biomass values of 

 total zooplankton tended to be larger at the 

 seaward stations during the CalCOFI cruise. This 

 difference is most likely related to the greater 

 number and narrower, vertical width of the tows 

 taken during this cruise, and, to some extent, 

 growth and development of each life stage as well 



130 



125^ 



120" 



115^ 



Q 



I— 



25 



O SOE 22 27 JUL- 20 AUG 1970 



• CALCOFI 7008 '6-27 Auo 1970 



  I  ... I I l__l 1 i I 1 1 1 1 L- 



25 



-Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



130 125" 120 115 



W. LONGITUDE 



Figure 1. -Positions of the day-night stations in the central 

 portion of the California Current. 



927 



