FISHERY BULLETIN: VOL, 78, NO. 3 



Figure 3.— Water transparency (5-d 

 averages) at Henderson Inlet and Clam 

 Bay as measured with a Secchi disc for 

 the period May 1974 to March 1975. 



2 5 

 UJ 



< 



Q- , 



in t 



z 

 < 



z- 



CLAM BAY 

 HENDERSON 



SEPT 



1974 



JAN FEB MARCH 



1975 



X 

 UJ 



8.0 



Clam Bay 

 Henderson Inlet 



British Columbia wild 

 population (Butler 1964) 



Jul Aug Sep Oct Nov Dec Jon Feb Mar Apr 



Figure 4. — Mean weights of juvenile spot prawns reared in net 

 pens at Clam Bay and Henderson Inlet compared with a wild 

 population in British Columbia (Butler 1964). 



Henderson Inlet and Clam Bay were 19.0° and 

 16.5° C. Daily fluctuations up to 4° C were seen at 

 both sites and the daily surface water tempera- 

 tures at Henderson Inlet averaged 2.5° higher 

 than at Clam Bay. The weekly mean temperatures 

 never exceeded the optimal 18° C value at either 

 site (Figure 2). 



To evaluate the effect of temperature on the 

 growth ofjuvenile prawns, the mean weight of the 

 prawns was plotted against cumulative degree 

 days (Figure 5). If temperature were the primary 

 variable controlling growth within the prawns' 



▲ — ▲ Henderson Inlet 

 Clam Bay 



500 1000 1500 2000 



CUMULATIVE DEGREE DAYS 



FlCiURE 5. — Average weight ofjuvenile spot prawns as a function 

 of cumulative degree days in the rearing experiments July to 

 December 1974. 



zone of anabolism, then the curves (Figure 5) 

 would be similar; however, this is not the case, as 

 growth was depressed at Henderson Inlet. The 

 slopes of both curves parallel each other after Sep- 

 tember, indicating that temperature had become 

 the major factor affecting growth. Beginning in 

 September there was a general decrease in water 

 temperature at both sites (Figure 2). 



To evaluate the growth of our prawns relative to 

 the growth of wild populations, we compared our 

 data with those of Butler (1964) who studied 

 growth of a wild population in British Columbia. 

 The data indicate the growth rate (increase in 

 weight over time) of the cultured prawns was simi- 

 lar to that of the wild population up to the end of 

 October (Figure 4). After October, the cultured 



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