Kane: Zooplarrkton biomass and species abundance on Georges Bank 



471 



8000 



6000 



4000 



2000 



4-4.9 5-5.9 



Degrees (°C) 



6-6.9 



Figure 6 



Ten-year median abundance of Centropages hamatus during 

 the winter season at 1°C surface temperature intervals. Popu- 

 lation estimates are from the central shoal depth area only. 



seasonal highs for the ten-year period. Calanus pin- 

 marehicus, P. minutus, and C. typicus were all below 

 average abundance in the low biomass years of 1982 

 and 1985. 



No strong correlation between median surface tem- 

 peratures and biomass was evident during the sum- 

 mer. Calanus finmarchicus abundance estimates were 

 highest at stations where surface temperatures had 

 warmed above 17°C, reflecting their shift to warmer 

 waters outside the 100-m isobath in summer 

 (Fig. 4). This relationship is probably related 

 to the cooler water found below the seasonal 

 thermocline (Manning and Holzwarth, 1990), 

 rather than to the warm surface layer where 

 this cold water species is unlikely to concen- 

 trate. Abundance of other species was vari- 

 able over the range of summer temperatures. 



Early autumn Four high biomass years, 

 from 1977 to 1980, were followed by dimin- 

 ishing ones through 1983 (Table 5E). Biomass 

 began to climb in 1984 and again reached 

 high levels in 1985. Standing stock fell to its 

 lowest level in 1986. The depth distribution 

 of the high biomass of 1980 differed substan- 

 tially from average conditions (Fig. 4). Me- 

 dian biomass from the intermediate (39cc/ 

 100 m ;i ) and deep (30.5cc/100m 3 ) water zones 



P. minutus 

  C. finmarchicus 



Figure 7 



Median abundance of Calanus finmarchicus and Pseudo- 

 calanus minutus in 1977 through 1986 during (A) early spring 

 and (B) late spring. 



E 

 o s 



•D 



Figure 8 



Median late spring abundance of Centropages hamatus, Calanus fin- 

 marchicus, and Pseudocalanus minutus in the central shoal depth region 

 in 1977 through 1986. 



