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Fishery Bulletin 9 1(3), 1993 



There were two notable annual distribution shifts 

 in late spring. Calanus finmarchicus abundance was 

 usually sparse within the 60-m contour and evenly 

 distributed offshore of it (Fig. 4). However, in the high 

 biomass years of the late 1970s, the population thrived 

 in central shoal waters. From 1977 to 1979, C. fin- 

 marchicus medians were 48,366, 33,397,and 15,364/ 

 100 m 3 respectively, while other years were all below 

 5000/100 m 3 . Metridia lucens abundance in deep water 

 peaked in 1979 (Table 3C) and they extended their 

 range of dominance inshore across the 100-m contour 

 line. Its high abundance (median = 22,015/100 m 3 ) in 

 the intermediate depth zone, where its 10-year me- 

 dian was 365/100 m 3 , elevated biomass there to nearly 

 double the time-series median, despite only average 

 C. finmarchicus abundance. The M. lucens abundance 

 peak in 1979 accounts for the high biomass measured 

 in that year. 



Centropages hamatus was the dominant copepod spe- 

 cies in the central shoals area during 1980 and 1981 



observed 



predicted 



o 



Q. 



E 

 a> 

 h- 

 c 



<B 



CD 



Figure 5 



Seasonal median surface temperatures and the ones predicted from the 

 harmonic regression model. Terms in the model are denned as follows: CA 

 = Cos(0.0172*sampling midpointijday i>: SA = Sim0.0172*sampling 

 midpoint(jday)!. 



and from 1983 to 1986. In other years, their numbers 

 were sparse there; median values fell below 1000/100 

 m 3 (Table 1C). Their high years correlated with all but 

 one (1981 — P. minutus) of the low abundance years for 

 C. finmarchicus and P. minutus (Fig. 8). 



The strongest relationship between abundance and 

 surface temperature variability in late spring (Table 

 2) was for C. hamatus numbers in the central shoals 

 area. Five of the six years, during which they domi- 

 nated those waters, temperatures were warmer than 

 average, and three of the four years in which they 

 were sparse were below the ten-year median tempera- 

 ture. Biomass and other dominant species abundance 

 could not be related to interannual differences in me- 

 dian surface temperatures. 



Summer The spring zooplankton biomass surge of the 

 late 1970's continued through the summer months. Bio- 

 mass levels in those years and in 1981 were signifi- 

 cantly different (P<0.05) from the low measures ob- 

 tained in 1982 and 1985 (Table ID). 



Centropages hamatus was prevalent in 

 the well mixed central shoals, but Georges 

 Bank as a whole was not dominated by one 

 copepod species during summer months 

 (Table ID). Biomass in 1977 was elevated 

 when C. finmarchicus and P. minutus abun- 

 dance reached near seasonal highs during 

 the ten-year period. Notable in 1977 was 

 that C. hamatus numbers in shallow water 

 were minimal and C. finmarchicus abun- 

 dance there (8386\100m 3 ) was at its 

 summer high, reinforcing the inverse abun- 

 dance relationship observed between them 

 in late spring. As it did in late spring, high 

 M. lucens abundance outside the 60-m 

 isobath raised biomass in 1979. Its abun- 

 dance within the intermediate depth zone 

 (4193\100m 3 ) was well above its 10-year 

 median there of 167M00 m 3 . Biomass in 

 1981 was raised when both P. minutus and 

 C. hamatus abundance estimates reached 



