28 



Fishery Bulletin 102(1) 



Figure 1 



Scale from a 352-mm FL male juvenile coho salmon 

 (Oncorhynchus kisutch) caught during the August 2000 

 GLOBEC cruise showing the axis of measurement (black 

 line), the focus (F), the mark of ocean entry (OE), and the 

 scale margin (SM). 



and the instantaneous growth rate in weight: 



G = (MWt)-MWt 0E ))/M, 



where Ad = estimated days between ocean entry and cap- 

 ture, were estimated for each salmon. 



The meaning of the instantaneous growth rate G can be 

 stated as follows: if salmon growth is exponential between 

 ocean entry and capture, then 



Wt 



Wt„ 



and at any instant the fish's weight increases at the rate of 

 G of its body weight per day. G can be multiplied by 100 to 

 give the instantaneous growth rate in terms of percentage 

 of body weight per day. 



Although the dates of ocean entry of individual lish 

 were unknown, seaward migration of coho salmon smolts 

 in California, Oregon, and Washington rivers occurs mainly 

 between mid-April and mid-June, and there is no consis- 

 tent latitudinal trend in timing of the migration ( Weitkamp 

 et al., 1995). Peak downstream migration of coho salmon 

 smolts was between mid-May and very early June in the 

 Columbia River estuary, 1978-83 (Dawley et al., 1985), 

 and in the lower Trinity River, California, 1997-2000 (US- 



A FL (mm) vs scale radius (mm) 



GM Regression: FL = 152.22 SR +36.07 

 r 2 = 0.94, n=370 



1 2 



Scales radius (mm) 



B Wt(g)vs FL(mm) 



In(WI) = 3.2273'ln(FL) - 12 6329 

 or Wt(g) = 3.263x1 (T 5 FL(mm) 32273 

 n=1018V = 0.99 



s 



— 5 



In (FL) 



Figure 2 



(A) Regression of fork length (FL) on scale radius and. 'Bi 

 regression of ln(WY) on ln(FL) for juvenile coho salmon {On- 

 corhynchus kisutch) caught during the May 1998-September 

 2000 Columbia River plume study. 



FWS 3 ). In 2000, peak downstream migration of mainly 

 nonhatchery coho salmon smolts at 13 monitoring sites in 

 coastal Oregon rivers north of Cape Blanco occurred from 

 April 2 to May 20; median peak migration occurred 26 April 

 ( Solazzi et al. 4 ) From the information available on timing of 

 seaward migration of coho salmon smolts. we used an ocean 

 entry date of 15 May when calculating Ad and estimating 

 ocean growth rates of unmarked coho salmon from scales. 

 In addition to estimating growth rates of juvenile 

 coho salmon from scales, we also estimated instantaneous 

 growth rates in weight between hatchery release and cap- 

 ture in the ocean of 28 coded-wire-tagged (CWT) juvenile 

 coho salmon: 



USFWS (U.S. Fish and Wildlife Service). 2001. Juvenile sal- 

 monid monitoring on the mainstem Klamath River at Big Bar 

 and mainstem Trinity River at Willow Creek, 1997-2000, 106 p. 

 Annual report of the Klamath River Fisheries Assessment Pro- 

 gram. Areata Fish and Wildlife Office, Areata, CA 9552 1 . 

 Solazzi, M.F., S.L.Johnson, B.Miller, and T.Dalton. 2002. Sal- 

 monid life-cvele monitoring project 2001. Monitoring program 

 report OPSW-ODFW-2002-2, 25 p. Oregon Dept. Fish and 

 Wildlife, Portland. OR 97207. 



