MOSHER: SCALE FEATURES OF SOCKEYE SALMON 



predominated in all sections of this geographical 

 area; however, in some years age 2. fish may 

 be abundant in the Nass River. 



Most scales of fish from the rivers identified 

 in this plate do not differ much between areas. 

 (Scales from sockeye salmon from Rivers and 

 Smith Inlets and some from the Nimpkish River 

 are distinct and are shown on Plate 9.) Fresh- 

 water zones on the scales of fish from the Nass 

 and Skeena Rivers tend to have slightly fewer 

 circuli, and those from the Columbia River slight- 

 ly more circuli than those from the Nimpkish 

 and Fraser Rivers. (Scales from sockeye salm- 

 on from the Nimpkish River which are repre- 

 sented by the primary mode in column 20 of 

 Table 4 are not pictured here as they are similar 

 to the scales of Fraser River fish.) The fresh- 

 water circuli of scales from fish of these areas 

 are mostly regular and unbroken. These char- 

 acters give the freshwater zone a clear-cut ap- 

 pearance. Plus growth is often present. 



The first ocean zone is usually distinct and 

 well marked. There are numerous circuli in this 

 zone, and even if some of them are irregular or 

 broken, the zone usually has a clear-cut appear- 

 ance. The spacing of circuli tends to be uniform, 

 but a few wider spaced circuli may occur at any 

 position within the zone. Scales from the Nimp- 

 kish River tend to have the most circuli of any 

 of these areas. Adventitious marks are common 

 in the ocean zones, but in spite of these irreg- 

 ularities, the circuli and winter marks are gen- 

 erally distinct and easy to count and measure. 



Geographical Areas with Distinctive Scale Types 

 (Plates 8 and 9) 



There are two types of scales showing this 

 freshwater age which are distinctive: 



1. The "Fish Creek" type (Plate 8), so called 

 because it was first observed in Fish Creek, 

 Knik Arm, Cook Inlet, but later also found 

 in small numbers in some other streams 

 as noted below . 



2. The "Rivers Inlet" type (Plate 9), so called 

 because it was first observed in Rivers In- 

 let, B.C., but later found in some other 

 areas, also noted below. 



Fish Creek Type {Plate 8; Tables U and 5) .— 

 Fish Creek type scales are on most sockeye 

 salmon from Fish Creek. A few were also found 

 in the samples from Adak and Unalaska Islands 

 and in the recently available samples from Fra- 

 zer Lake (Kodiak Island) and the Nimpkish 

 River (fish with more than 20 circuli in column 

 20, Table 4). 



Fish Creek type scales are characterized by a 

 large freshwater zone with many well-marked 

 circuli. There is often a check or winter mark 

 about 18 or 20 circuli from the center of the 

 scale, followed by a few circuli of plus growth. 



The circuli of the first ocean zone are also 

 well marked, and in most cases, well separated, 

 sometimes with an area of wider spaced circuli 

 near the freshwater zone like most of the Bristol 

 Bay fish. The numbers of circuli in this zone 

 tend to vary with the locality from which the fish 

 came: Adak and Unalaska Island, less than 22 

 circuli; Fish Creek and Kodiak Island, 22-27 

 circuli; and the Nimpkish River, over 27 circuli. 



The annual number of adult fish with this scale 

 type from all areas is relatively small (perhaps 

 in the neighborhood of 100,000 fish as a max- 

 imum) , but the scales have been observed' in off- 

 shore samples because of their distinctive ap- 

 pearance (Mosher et al, 1961). 



Rivers Inlet Type {Plate 9; Tables U and 5) .— 

 Gilbert (1914) first noted that scales of sock- 

 eye salmon from Rivers Inlet and later from 

 Smith Inlet were diflTerent from those of other 

 areas. Recently, samples from the Nimpkish 

 River (on Vancouver Island, which empties into 

 the northern end of Johnstone Straits near Riv- 

 ers and Smith Inlets) became available. Some 

 of these scales were also of the Rivers Inlet type. 



These scales are characterized by a small, dif- 

 fuse freshwater zone with very few circuli. 

 Usually the circuli are broken, irregular, crowd- 

 ed together and difficult to count. The transition 

 from freshwater to ocean growth is usually dif- 

 fuse and difficult to distinguish. 



The first ocean zone, the distinctive feature of 

 these scales, has many uniformly spaced circuli, 

 usually with no area of wider spacing. This 

 first ocean zone often looks like freshwater 



173 



