FISHERY BULLETIN: VOL. 75, NO. 4 



it is likely that the population had been lightly 

 exploited prior to 1969. Results of electrofishing 

 surveys apparently stimulated greater fishing 

 effort. Shape of the 1970 catch-frequency curve 

 resembled those of public ponds, except that sub- 

 stantial numbers of age 4 and older trout were 

 harvested. 



Size selection by anglers at Maxwell Springs 

 was reflected in the relative rates of natural and 

 fishing mortality. For ages 2-5 trout, mean total 

 mortality rates from spring to fall increased with 

 age and were paralleled by fishing mortality (Fig- 

 ure 6). Natural mortality changed little with age 

 of fish. Differences between natural and fishing 

 mortality were greatest for age 5 trout and fish- 

 ing mortality accounted for 69% of their total 

 mortality. 



25 



3 20 

 o 



1.0 



tr 



o 



2 

 to 



O 



i2 0.5 



V) 



z 



O TOTAL 

 ▲ NATURAL 

 □ FISHING 



171'- 



- 1 



5+ 



AGE 



FIGURE 6.— Instantaneous rates of total, fishing, and natural 

 mortality (spring to fall) of ages 2 to 5 trout at Maxwell Springs. 

 Data points are 2-yr means, 1969-70. 



Production 



Production was most influenced by numbers of 

 fingerlings hatched in ponds and numbers of 

 immigrants. Growth rates varied little among 

 populations, hence year class biomass had the 

 most effect on production. Among populations 

 annual production ranged from 26 kg/ha at 

 Clubhouse Springs to 331 kg/ha at Maxwell 

 Springs (Table 10). 



Annual production in Clubhouse Springs was 

 dependent upon biomass of ages 1 and 2 trout. 

 Few fingerlings immigrated into the pond and 



TABLE 10. — Production (kilograms per hectare) by age-group 

 of brook trout in study ponds. Production by age trout during 

 fall to spring intervals covers the period from 1 March to end 

 of interval. Production by age 4 trout includes all older age- 

 groups. Total annual production was expressed in terms of 

 365 days. 



Site and 

 interval 



Annual 

 Total total 



Clubhouse 

 Springs: 



27 Mar. 1968 



28 Aug. 1968 

 8 Apr. 1969 

 8 Sept. 1969 



1 Apr. 1970 

 8 Sept. 1970 



29 Apr. 1971 

 8 Sept. 1971 



21 Apr. 1972 

 Hoglot 

 Springs: 



2 Apr. 1968 

 21 Aug. 1968 



8 Apr. 1969 



8 Sept. 1969 

 1 3 Apr 1 970 



8 Oct 1970 

 28 Apr. 1971 

 21 Sept. 1971 



2 May 1972 

 Maxwell 

 Springs: 



6 Apr. 1969 

 13 Oct. 1969 

 26 Mar. 1970 



6 Oct. 1970 

 26 Apr. 1971 

 20 Sept. 1971 

 26 Apr. 1972 



3.9 

 4.0 

 5.6 

 1.5 

 5.5 

 6.1 

 1.8 

 2.7 



10.6 

 13.4 

 18.5 

 15.5 

 11.5 

 7.7 

 5.9 

 10.2 



17.5 

 24 

 38.7 

 20.4 

 22.9 

 3.1 



0.5 



1.0 

 0.6 

 1.4 

 0.8 



7.9 

 -0.3 

 4.6 

 2.7 

 3.0 

 1.4 

 0.6 

 1.3 



37.0 

 1.7 



12.2 

 8.6 

 6.1 

 1.2 



36.6 

 9.9 

 23.4 

 1.9 

 36.8 

 21.3 

 13.6 

 11.7 



111.8 

 31.1 



118.1 

 40.5 



146.9 

 48.7 

 92.9 

 33.9 



288.3 

 30.2 



239.5 

 83.0 



172.3 

 39.7 



45.3 



25.8 



54.1 



25.9 



141.4 



156.4 



187.9 



125.4 



331.2 



297.2 



211 4 



'Age at end of interval. 



they contributed only 109c of total annual 

 production. Highest annual production occurred 

 in 1970 when the population was bolstered by 

 high levels of immigration during winter 1969-70 

 and in summer 1970. Low biomass in spring and 

 below average rates of immigration in 1969 and 

 1971 resulted in low annual production. 



At Hoglot Springs, annual production was most 

 affected by numbers of fingerlings hatched in the 

 pond and numbers of immigrants. Age trout 

 accounted for nearly 32% of average annual pro- 

 duction. Annual production peaked in 1970 (Table 

 10) when large numbers of age 1 trout immigrated 

 oversummer and cohort biomass increased from 

 13 kg/ha in spring to 91 kg/ha in fall. 



Annual production in Maxwell Springs was 

 related to the number of strong year classes 

 present and their subsequent biomasses. The 

 highest annual production was in 1969 when two 

 large age-groups were present (1968 and 1969 

 year classes), and there was a high biomass of 

 age 2 and older trout (Table 10). In 1971, the 

 year of lowest production, the only large age- 

 group was the fingerlings. In all years, production 



760 



