FISHERY BULLETIN: VOL. 74, NO. 1 



Samples were preserved with Formalin at sea 

 and sorted into taxonomic groups ashore. Wet 

 (drained) weights were obtained for micronekton 

 (fishes, shrimps, and squids). Micronekton from 32 

 different IKMT collections were dried to a con- 

 stant weight in a drying oven at 65°C. The mean 

 dry weight: wet weight ratios were then used to 

 convert wet weights of other collections to dry 

 weights. The means and standard deviations of 

 the dry:wet weight ratios were 0.23 ± 0.06 for 

 fishes, 0. 15 ± 0.02 for shrimps, and 0. 1 1 ± 0.04 for 

 squids. 



Dry weights were obtained for all major taxa 

 sorted from MN samples: euphausiids, copepods, 

 chaetognaths, medusae, amphipods, salps-dolio- 

 lids, and shrimps. These taxa generally com- 

 prised over 95% of the total collection weights. The 

 remainder usually consisted of annelids, 

 pteropods, and heteropods. Ctenophores usually 

 disintegrated in the samples, but when fragments 

 were identifiable they were weighed with the 

 medusae. In this paper, dry weights are used as a 

 measure of standing stock, which is considered to 

 be synonymous with biomass. 



Sampling Variability 



Several series of IKMT's at a single station 

 during a single night were taken to assess sam- 

 pling variability. The variability of total micro- 

 nektonic dry weight per 1,000 m^ (Table 1) indi- 

 cates that the variance for these series was ap- 

 preciably less than the mean. These data on total 

 biomass of micronekton, which are not in dis- 

 agreement with the high variability encountered 

 for individual species of micronekton captured 

 in repeated tows at one station (e.g., Pearcy 1964; 

 Ebeling et al. 1970), suggest that most of the 

 temporal fluctuations of biomass illustrated in 



Table l. — Sampling variability oftotal biomass of micronekton 

 and macroplankton (grams dry weight per 1,000 m^) collected 

 during repeated tows during separate nights. 



Figure 2 are independent of short-term sampling 

 variability. 



Variances of macrozooplankton biomass from 

 repeated MN tows, on the other hand, were much 

 larger than those for the IKMT (Table 1). In two 

 out of the five series, variance surpassed the mean. 

 Hence, a larger portion of the temporal variability 

 of zooplankton can be ascribed to sampling varia- 

 bility. 



RESULTS 



Micronekton 



Variations of the dry weights of micronekton 

 (fishes, shrimps, and squids) captured per 1,000 m^ 

 are shown in Figure 2 for four stations, 1962-67. 

 Several trends are apparent. Seasonal peaks in 

 the biomass occur inshore at the 28- and 46-km 

 stations during the winter months, with very low 

 values during intervening months. A reversed 

 trend, though less pronounced, is found offshore at 

 the 84- and 120-km stations where maximum 

 catches generally were made during the summer 

 or fall months. Average biomass values appear to 

 be lowest inshore, highest at 84 km, and lower 

 again at 120 km where total variability is the 

 lowest. 



The spatial peak of micronekton biomass at 84 

 km is more obvious in Figure 3, where dry weight 

 is plotted per square meter instead of per cubic 

 meter (to compensate for different depths of sam- 

 pling at inshore stations). The standing stocks of 

 fishes were greater than shrimps, and shrimp 

 stocks were greater than squids at all stations 

 except at 46 km where shrimps predominated. The 

 neritic, benthopelagic shrimp, Pandalus jordani, 

 occasionally made up the bulk of the biomass of 

 collections at both 28 and 46 km (Pearcy 1970). 

 However, mesopelagic animals comprised most of 

 the nighttime IKMT catches: mainly the fishes 

 Stenobrachius leucopsarus, Diaphus theta, Tar- 

 letonbeania crenularis, and Tactostoma macropus 

 (Pearcy 1964, 1972; Pearcy and Laurs 1966; 

 Pearcy and Mesecar 1971); the shrimp Sergestes 

 similis (Pearcy and Forss 1966, 1969); and the 

 squids Gonatus spp. and Abraliopsis felis (Pearcy 

 1965, 1972). 



Seasonal variations in the total biomass 

 (grams/10 m^) of micronekton are illustrated in 

 Figure 4 for two general seasons: May-October, 

 which includes the upwelling season; and 

 November-April, when surface currents are usu- 



72 



