of life* The time of annulus formation is uniform regardless of the 

 time of hatching, and annuli would, therefore, appear on the scales 

 after 6 months to 1 year of life, depending on when the fish began inde- 

 pendent existence* Growth rates established in this manner are probably 

 low. Larger fish were usually missed by the fyke nets. Beyond the arbi- 

 trary limit of 80 millimeters (3.15 inches), the samples are inadequate. 



The step-like character of the growth curves expresses the length 

 of growing seasons in Trinity River at and above Lewis ton. Apparently, 

 growth is quite rapid after emergence of fry from the gravels. This 

 acceleration slows to a virtual standstill by September, emd average 

 lengths are almost constant throughout the winter. Increases in length 

 begin in spring (March to May, depending on the year) and presumably 

 continue until the following September, although catches of older steel- 

 head are insufficient to determine the time of growth cessation in the 

 second year of life. 



The greatest number of downstream migrating steelhead as determined 

 by f^e netting, move shortly before or somewhat after the end of the 

 first year of life. However, many migrant steelhead must be larger 

 than those sampled by the fyke nets, as scale studies of adults show 

 that many individuals remain in the stream two or three years before 

 reaching the ocean. It is likely that' young steelhead leave the Lewiston 

 area as yearlings and spend a year or more completing their migration 

 to the sea* Certainly the compesltion of migrants passing Lewiston is 

 not necessarily the same as that of migrants entering the Klamath River 

 or the ocean. During extended winter dry periods when the river is low 

 and clear, groups of several hundred steelhead trout 6 to 8 inches in 

 length can be seen slowly drifting downstream. The size of these fish 

 would indicate that they were in 'Oieir second or third year of life* 

 These schools migrate down the center of the river hovering close to 

 the bottom, thus eluding the fyke nets which, because of excessive 

 current in midstream, were fished near the bank. 



Prior to or during the seaward movement, steelhead trout become 

 large enough to add materially to the fish population available to 

 anglers, (ihere is no size limit in California.) The magnitude of 

 the contribution to the sports fishery is not known, but it is etssuned 

 to be considerable* 



Steelhead remain in the ocean from one to three years before making 

 their first upstream migration to spawn. Mtoy of them do not die 

 following spawning, but return to the ocean. Before completing their 

 life history, steelhead may spawn three or four times, repeating this 

 migratory procedure each year after maturity. 



46 



