population size at peak emergence in salmonid 

 populations (Hunt 1966; O'Connor and Power 

 1976). Total production of each species was divided 

 by the smallest stream area within the 100 m 

 section that was recorded during the study in 

 order to give an estimate of production per unit 

 area. 



Results and Discussion 



Recently emerged coho and chinook salmon 

 were first observed in Orwell Brook in 1978 on 

 May 13. In 1979, coho salmon were first observed 

 on May 9th and chinook salmon on May 10. Peak 

 emergence of both species occurred during early 

 June 1978. Steelhead began emerging during 

 mid-June and peaked in early to mid-July. 



Population estimates were initiated in mid- 

 June about 2 wk after peak salmon emergence. At 

 this time both salmon species were abundant in 

 the main stream and steelhead had started to 

 emerge. Estimates of population size at peak 

 emergence were 718 coho salmon and 189 chinook 

 salmon fry/lOO m in the section (Table 1). Densi- 

 ties of fry (number per square meter) at this time 

 were 1.30 and 0.34 for coho and chinook salmon 

 (Table 1). The initial estimate of steelhead in June 

 was 103 fry/lOO m or 0.20 fry/m^ of stream bottom. 

 However, the highest densities of steelhead fry 

 were not recorded until August (Table 1). 



Total production of subyearling coho salmon 

 from 1 June to 30 October 1978 was 1,248 g. This 

 was substantially greater than production of 

 chinook salmon, 282 g and steelhead, 404 g (17 

 June-10 October) (Figure 2). Production per 

 square meter was 2.7, 0.6, and 0.9 g for coho and 

 chinook salmon and steelhead. Combined total 

 production of the three species was 4.2 g/m"' for the 

 period of study. 



Production of subyearling coho salmon in Or- 

 well Brook during 1978 was intermediate between 



Table l. — Estimated monthly numbers (with 95% confidence 

 limits) and densities (number per square meter) of subyearling 

 coho salmon, chinook salmon, and steelhead in 100 m study area 

 of Orwell Brook, Oswego County, N.Y., during 1978. 



o 

 c 



ad 



UJ 



o. 



C 



z 



o 

 o 



LU 



c 



>- 



O 



d 



250 1 



200 



150 



TOO 



50 



300 

 250 

 200 

 150 

 100 

 50 4 



CHINOOK 



10 Sept. 



10 Oct. 



1 2 3 



MEAN WEIGHT (R) 



STEELHEAD 



17 June 



'Logarithmic extrapolation. 



0.5 1,0 1.5 2.0 2.5 



MEAN WEIGHT (g) 



Figure 2. — Production curves of subyearling coho and chinook 

 salmon in Orwell Brook, Oswego County, N.Y., 1 June-10 October 

 1978, and steelhead 17 June-10 October 1978. 



552 



