FISHERY BULLETIN: VOL. 75, NO. 4 



TABLE 7. — Estimated mean annual lengths (millimeters) and 

 weights (grams) of brook trout on 15 April and 15 September. 

 Data from Clubhouse and Hoglot springs were from 1968-71 

 and those from Maxwell Springs were from 1969-72. 



Clubhouse Springs were from 58 to 90% larger 

 than spring yearlings in Hoglot or Maxwell 

 springs. Although trout in Clubhouse Springs 

 maintained a size advantage over their counter- 

 parts in the other ponds after the first growing 

 season, age-specific instantaneous growth rates 

 for all populations were similar. I compared mean 

 age-specific growth rates for intervals of April to 

 September and September to April for ages 1-3 

 trout. There were no significant differences for 

 similar age trout among populations U-test 

 P>0.05). During summer instantaneous growth 

 rates of trout tended to be highest in Maxwell 

 Springs, but there were no consistent differences 

 during winter intervals. 



Growth rates of fingerling trout were inversely 

 related to their density (number or weight) when 

 data from all populations were combined (Table 

 8). Density of yearling trout also had an effect 

 on growth of fingerlings; correlation coefficients 

 were highest when fingerling growth was related 



to combined density of fingerlings and yearlings. 

 Effects of density on growth rates of age 1 and 

 older trout were inconsistent. When instan- 

 taneous growth rates were used as the dependent 

 variable and density in numbers or weight was 

 the independent variable, correlation coefficients 

 were consistently low (Table 8). When age-specific 

 growth was expressed as mean weight or length 

 in September or weight gain from April to Septem- 

 ber, correlation coefficients were consistently 

 high (Figure 4). The lack of correlation between 

 instantaneous growth rates and density may have 

 been due to underestimation of mean weights of 

 trout in fall, particularly in Clubhouse Springs. 

 Biases could have resulted from: 1) immigration 

 of trout smaller than pond residents, 2) differen- 

 tial exploitation of faster growing individuals in 

 a year class, and 3) errors in estimating year class 

 densities. The lack of correspondence between 

 instantaneous growth rates and other growth 

 parameters has been noted in other studies 

 (Eipper 1964). 



Harvest 



Fishing success and harvest of trout were in- 

 fluenced by trout densities and fishing pressure. 

 Maxwell Springs supported the largest trout 

 population in 1969 and 1970 and catch rates were 

 highest (Table 9). Among populations annual 

 catch rates were positively related to spring 

 densities of age 1 and older trout (r = 0.88; 

 P<0.01). There was a significant correlation be- 

 tween biomass of trout harvested (yield) and the 



TABLE 8. — Linear correlation coefficients for growth and density of trout ages to 3 

 in study ponds, (df = 10; *P<0.05, **P<0.01.) 



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