that observed in Oregon, 5.6 g/m^ (Chapman 1965) 

 and Michigan, 0-1.9 g/m^ (Stauffer^) during a 

 similar time interval. Production of coho salmon 

 in the 100 m section of Orwell Brook from 1 June to 

 15 October 1977 was 5.9 g/m^ (Johnson 1978). Al- 

 though the 1978 production estimate for coho 

 salmon represents a 549c decrease from 1977, the 

 variation in production between years is within 

 the range reported by Chapman (1965) for coho 

 salmon in Oregon coastal streams. 



No information on chinook salmon production is 

 available for the Great Lakes region; however, 

 production of chinook salmon in Orwell Brook was 

 intermediate to that recorded in the Lemhi River 

 and Big Springs Creek, Idaho (Goodnight and 

 Bjornn 1971). Production of steelhead is less 

 than recorded in Michigan (Hannuksela^°) and 

 intermediate between the two Idaho streams 

 (Goodnight and Bjornn 1971). 



From emergence in May until the termination 

 of sampling in November, subyearling coho salmon 

 were larger than either subyearling chinook 

 salmon or steelhead (Table 2). However, since 

 chinook salmon characteristically leave their 

 natal streams earlier than coho salmon, larger 

 chinook salmon smolts may be migrating early. 

 The growth rate (total length in millimeters per 

 day) of coho and chinook salmon and steelhead 

 was greatest during the first 2 mo following 

 emergence (Table 2). Growth during this 2 mo 

 period was 0.44, 0.47, and 0.39 mm/d for coho and 

 chinook salmon and steelhead (Table 2). High ini- 

 tial growth rates of subyearling coho salmon and 

 steelhead have previously been reported by 

 Chapman (1965) and Stauffer (footnote 9). For the 

 entire period (175 d for salmon, 145 d for 

 steelhead) the growth rates of chinook salmon and 

 steelhead were identical, 0.27 mm/d, with coho 

 salmon being only slightly slower, 0.26 mm/d. In 

 Michigan, growth rates of subyearling coho salm- 

 on and steelhead from June to November were 

 0.29 and 0.26 mm/d (Stauffer footnote 9). However, 

 although these estimates are similar to those ob- 



TabLE 2. — Number examined, mean total length (millimeters) 

 (with 95% confidence limits), and daily growth increments 

 (mm/d) of subyearling coho salmon, chinook salmon, and 

 steelhead from Orwell Brook, May-November 1978. 



Coho salmon 



Chinook salmon 



Steelhead 



^Stauffer, T. M. 1975. Population characteristics and 

 summer-to-autumn survival of juvenile rainbow trout and coho 

 salmon in two Lake Superior tributaries, 1969-1972. Mich. 

 Dep. Nat. Resour, Fish. Res. Rep. 1825, 21 p. Institute for 

 Fisheries Research, Museums Annex Building, Ann Arbor, MI 

 48109. 



'"Hannuksela, P R. 1973. Food interrelationships of the 

 mottled sculpin, Cottus bairdi, and juveniles of the rainbow 

 trout, Salmo gairdneri, in a tributary of Lake Superior. Mich. 

 Dep. Nat. Resour., Fish. Res. Rep. 1801, 21 p. Institute for Fish- 

 eries Research, Museums Annex Building, Ann Arbor, MI 

 48109. 



Date No. TL mm/d No. TL mm/d No. TL mm/d 



18 May 10 45.1 ±4.4 10 36.7±3.9 



0.65 0.34 



17June 20 63.6-5.7 20 46.7-1.9 10 297±1.8 



0.26 0.61 0.52 



16 July 40 711 ±2.8 40 64.5±20 30 44.9±1.6 



0.13 0.06 0.24 



12Aug. 30 74.7±2.5 20 66.0±3.0 25 51.5±1.7 



0.27 0.11 0.19 



lOSept. 20 82.4±4.9 20 69.2±3.0 30 570±3.2 



0.05 0.22 0.16 



lOOct. 20 83.9±49 10 75.7±3.4 25 61.7±3.8 



022 0.28 0.26 



9 Nov. 10 90.4±5.2 10 84.0±4.3 10 69.5±4.1 



tained in Orwell Brook, both coho salmon and 

 steelhead are initially larger in June in Orwell 

 Brook and this size differential (especially for coho 

 salmon) is retained throughout the fall. There is 

 no available information on chinook salmon 

 growth in the Great Lakes region; however, 

 growth in New York is slower than reported in 

 Washington (Becker 1973). 



Acknowledgments 



I wish to thank E. M. Zebisch for assistance in 

 the field and J. D. Sheppard and E. W. Radle for 

 reviewing preliminary drafts of the manuscript. 

 The comments and suggestions of two anonymous 

 reviewers substantially contributed to the content 

 of the final manuscript. 



Literature Cited 



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Becker, C. D. 



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553 



