FISHERY BULLETIN: VOL. 71, NO. 3 



Columbia River to supplement natural spawn- 

 ing and to compensate for loss of and damage to 

 natural spawning areas by construction of dams. 



A brief resume of the life history of these coho 

 salmon may be helpful. Most of the salmon used 

 in these studies were released as small fish dur- 

 ing April and May, approximately 1 yr after 

 hatching in the hatcheries. About 10% of them 

 were marked just before release. The young 

 salmon then migrated to the ocean. After a few 

 months in the ocean a relatively small portion 

 of the fish — mainly 2-yr-old males called jacks 

 — matured and returned to their hatcheries in 

 the Columbia River. At that time, a few were 

 captured in the Columbia River sport and com- 

 mercial fisheries. Most of the fish, however, 

 remained in the ocean over the winter. During 

 the following summer, many were captured in 

 the ocean commercial troll and sport fisheries. 

 During late August through October, all the 

 remaining fish (3-yr olds) from each brood then 

 began to mature and reenter the Columbia 

 River, where some were captured in the com- 

 mercial gill net and sport fisheries. Those escap- 

 ing these fisheries returned in the late fall to 

 their hatchery streams, where their eggs were 

 taken artificially for rearing in the hatchery. 

 Coho salmon, like all Pacific salmon, die after 

 spawning and the cycle is then complete. 



In a report by Wahle, Vreeland, and Lander,^ 

 the economic contributions of all hatcheries com- 

 bined have been analyzed for these two broods 

 of fish. These benefit/cost calculations rely 

 mainly on release and recovery data. Such 

 biological parameters as fishing and natural 

 mortality, age at maturity, abundance, and time/ 

 area distribution were not considered. These are 

 important in developing a proper management 

 plan for these fish, so we have developed esti- 

 mates of them for these two brood years. These 

 will be timely supplements to the benefit/cost 

 analysis of Wahle et al. (See footnote 2.) 



The estimates of survival, maturity, and 

 abundance in the present report mainly are 



average values for all hatcheries combined. 

 Limitations in the basic data reduce the relia- 

 bility of separate evaluations for hatcheries on 

 each of the four sections of the Columbia River, 

 particularly for the 1966-brood data. The dis- 

 tribution of hatchery fish in marine fisheries is 

 compared between the four river sections for 

 each brood. 



PROBLEMS OF ESTIMATING 

 PARAMETERS 



To aid in understanding the various param- 

 eters we wish to estimate, in Figure 2 we have 

 portrayed graphically certain features of the 

 coho salmon's life history, particularly as they 

 pertain to the various parameters for the period 

 from release as smolts until their return to the 

 Columbia River as adults — approximately 18 

 mo. The time sequence shown in Figure 2 is 

 accurate to approximately 0.5 mo. It readily 

 can be seen from Figure 2 that there are four 

 known values: 1) number of smolts released 

 (No), 2) number maturing as jacks (£"1), 3) num- 

 ber caught by the ocean troll and sport fisheries 

 (C), and 4) number returning as adults {E2). 

 From these four known values we wish to esti- 

 mate: 1) fishing mortality rate over the last 4.5- 

 mo period (F), 2) proportion maturing as jacks 

 (ni), 3) natural mortality rate for the 6.0-mo 

 period from release of smolts until the jacks 

 mature (Mi), 4) natural mortality rate for the 

 12.0-mo period from the time jacks mature until 

 the adults return to the Columbia River (M2), 

 5) number of coho remaining at sea when the 

 jacks have returned (Ni), and 6) number of coho 



E, 



4.5IFtMj) /^ \ 



2 Wahle, R. J., R. R. Vreeland, and R. H. Lander. Bio- 

 economic contribution of 1965-66 brood coho salmon 

 from Columbia River hatcheries. Columbia Fish. Program 

 Off., Natl. Mar. Fish. Serv.. NOAA, Portland, Oreg., and 

 Northwest Fish. Cent., Natl. Mar. Fish. Serv., NOAA, 

 Seattle, Wash. [Unpubl. manuscr.l 



6.0 13.5 



TIME SINCE RELEASE OF SMOLTS (MONTHS) 



Figure 2. — Diagram depicting the life history of the coho 

 salmon for the period from release of smolts until their 

 return to the Columbia River as adults — approximately 

 18 mo (circled items indicate observed data). 



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