Figure 2. — Teu-iiart saniiiling lU't used to olitain fish for marking and 

 to estimate the numbers of niarlied and unniarl<ed lisli released. 



;> and shown in figure .■!. (Teiienil saniplino- levels 

 for eacli time-location stratum were predeter- 

 mined; typically, about 20 percent of the catcli is 

 sampled for marks, and from 50 to 100 unmarked 

 fish are sampled to obtain age, leng-th, and weight. 

 Catch data for eacli time-location stratum are 

 ]irovided by the management agencies. For most 

 fisiieries, the catch of chiuook salmon in numbers 

 of fish is an estimate. Commercial catches are esti- 

 mated either from the total weight of landings and 

 an estimate of average fish size or from total 



salmon landings (numbers) and an estimate of 

 species composition. Estimates of sport catches are 

 from measures of total etiort and catch per-unit- 

 effort or from salmon punch cards (filled out by 

 anglers) together with independent sampling by 

 the management agency. 



Because the catch of liatchery-reared fish de- 

 pends on length and timing of the fishing seasons 

 as well as cm the numbers of fish available, an es- 

 tinnite of tlic numbers of hatchery fish which 

 escape the fishery is required to measure the 



CONTRIBUTION OF COLTMBI.\ RIVKR HATCHERIES TO FALL CHINOOK SALMON HARVEST 



305 



