FISHERY BULLETIN: VOL. 74, NO. 1 



vores at all stations. The high catches of 

 herbivores at 46 km were due to abundant 

 concentrations of euphausiids. Both groups of 

 carnivores, on the other hand, had lowest bio- 

 mass at the inshore stations and attained maxima 

 farther offshore. 



Seasonal variations in the standing stocks of 

 herbivores and planktonic carnivores are illus- 

 trated in Figure 7. Mann-Whitney U tests of 

 differences between the two seasons were not 

 significant (all P>0.1) for any station, providing 

 no evidence for seasonal changes in the biomass of 

 herbivores. The biomass of planktonic carnivores 

 increased wdth distance offshore during the winter 

 and tended to decrease during summer. The 

 biomass at 28 km was higher in summer than 

 winter (P<0.01), largely due to high catches of 

 medusae during the summer. At 84 km, 



50 



40 



30 



30 



E 

 Q 20 



Q. 



5 10 



a: 



Q 







20- 

 15- 

 10- 



^ 



PLANKTONIC 

 CARNIVORES 



MAY- 

 OCT 



■-^NOV-APR 



>i^ 



28 46 84 120 >I20 



DISTANCE OFFSHORE (km) 



Figure 7. — Seasonal variations in the average biomass (± 1 

 SE) of herbivores (upper) and planktonic carnivores (lower). 



^ 20 

 > 



O 



y 10- 



o 



PLANKTONIC 



NEKTONIC ■•■. 

 CARNIVORES'^ 



28 46 84 120 



DISTANCE OFFSHORE (km) 



>I20 



Figure 8. — Variability in the catches of herbivore, planktonic 

 carnivores, and nektonic carnivores vs. distance offshore. 

 Variability is expressed as coefficients of variation based on 

 dry weights per 1,000 m^. 



planktonic carnivores also appeared to be more 

 abundant during the summer (P = 0.08), again 

 because of higher catches of medusae. No seasonal 

 differences were apparent at other stations 

 (P>0.1). 



The ratio of herbivore:carnivore biomass, as 

 expected from the data shown in Figure 6, aver- 

 ages about 2.0 at 28 km and 4.0 at 46 km, but 

 only about 1.0 at the oceanic stations 84, 120, 

 and >120 km. These ratios were ranked among 

 stations for individual cruises. The sum of the 

 ranks for stations were significantly different 

 (P<0.01, Friedman two-way ANOVA by ranks, 

 Tate and Clelland 1957). Thus herbivores pre- 

 dominated over carnivores in inshore waters, 

 whereas the standing stocks of herbivores and 

 carnivores were about equal in oceanic waters 84 

 km offshore and beyond. No seasonal differences 

 in herbivore:carnivore ratios were found (P> 

 0.05, Mann- Whitney U tests). 



As a measure of variability of the standing 

 stocks of trophic groups over the sampling period, 

 coefficients of variation (six) of the catches are 

 plotted for each station in Figure 8. A marked 

 decline in the variability of both herbivores and 

 carnivores takes place from inshore into offshore 

 waters. 



DISCUSSION 



Regional Comparisons of 

 Zooplankton Standing Stocks 



Values for the standing stocks of zooplankton in 



76 



