tinuities were assumed to indicate annual marks. In assigning 

 ages, we allocated a birthday of 1 January for all species. 



Ages were determined in the laboratory by counting apparent 

 annulae in the structural pattern of whole otoliths and scales. All 

 age readings were performed by trained specialists at the NWAFC 

 Montlake Laboratory. Otolith rings were counted by viewing 

 whole otoliths, immersed in water, with direct lighting through a 

 binocular microscope at 7-10 x magnification. Scales were pre- 

 pared using the methods of Kennedy (1970) and rings were 

 counted with the aid of a projection viewer. 



To assess the reliability (precision) of age determinations, 789 

 skeletal structures, collected during the 1976 survey from seven 

 common Bering Sea fish species, were independently analyzed by 

 two of the age reading specialists (Table 4). Ages of young fish 

 were estimated most precisely. The age determinations of old fish 

 were less reliable due to narrowing and crowding of outer rings. 



Table 4. — Summary of comparisons of ages determined by (wo age reading 

 specialists. 











Percentage with 







Age 





perfect agreement 





Skeletal 



range 



Number of 



in age group 



Fish species 



structure 



(yr) 



comparisons 



assignment' 



Walleye 



Otoliths 1 



1-7 



87 



88 



pollock 





8-12 



84 



63 



Pacific cod 



Scales 



2-3 



58 



85 







4-6 



33 



79 



Yellowfin 



Otoliths' 



5-12 



180 



93 



sole 





13-16 



9 



67 



Alaska 



Otoliths' 



6-12 



25 



76 



plaice 





13-16 



11 



60 



Rock sole 



Otoliths 1 



3-12 



127 



83 







13-14 



7 



71 



Flathead 



Otoliths 1 



3-12 



53 



83 



sole 





13-15 



13 



70 



Greenland 



Otoliths' 



2-6 



66 



85 



turbot 





7-11 



36 



75 



'90% of all disagreements in age group assignment differed by only I yr. 

 'Saccular otoliths. 



Analytical Procedures 



See Table 5 for definition of symbols. 



Standardization of catches. — All trawl catches were stan- 

 dardized to a basic sampling unit, the weight of catch taken per 

 1.0 km trawling distance, including a scaling of each vessel's 

 fishing performance to that of the Miller Freeman: 



W. 



CPUE 



ijk 



ijk 



Da ■ R 



vk 



(1) 



where CPUE,^. is the catch per unit of effort (kg/km) for species 

 k for they th station in the /'th subarea; W ijk is the weight of catch 

 (kg), D- is the distance trawled (km) computed from the start and 

 ending loran-C readings at each station, and F vk is the relative 

 fishing power correction factor for vessel v in respect to species k. 

 Fishing power correction factors had previously been deter- 

 mined during the 1975 survey for the Anna Marie and Pat San 

 Marie relative to Miller Freeman (Pereyra et al. see footnote 2). 

 Because of the participation of the Oregon in the 1976 survey, ad- 

 ditional comparative fishing trials were conducted in an attempt 

 to intercalibrate the fishing efficiencies of all four vessels. Vessel 

 correction factors used for all subsequent analyses are given in 

 Table 6. 



Catch per unit of effort. — Mean CPUE by species and subarea 

 was computed using the mean per unit estimate: 



E cpuE 'v* 



CPUE,-* = ->=' 



(2) 



where n { is the number of successfully trawled stations in the fth 

 subarea. The variance of this estimate was: 



Table 5. — Summary of symbols used in the description of analytical procedures. 



Terms 





Terms 





A 



Geographical area (km 1 ) 



P 



Effective trawl path width (km) 



B 



Population weight (kg) 



1 



Coefficient of catchability (per km) 



C 



Coefficient of vulnerability (scalar) 



s 



Number of individuals within a subsample 

 (integer) 



CPUE Catch per unit of fishing effort (kg/km) 



l 



Age (yr) 



D 



Computed distance trawled (km) 



'o 



Hypothetical age of zero length (yr) 



F 



Relative fishing power correction factor 

 (scalar) 



W 



Individual weight (kg) 



K 



Growth completion rate (per yr) 



Subscripts 



L 



Number of length categories (integer) 



i 



Statistical subarea 



ice 



Mean asymptotic length (cm) 



j 



Station 



N 



Number of individuals within catch (integer) 



k 



Species 



P 



Population number (integer) 



1 



Individual length class 



S 



Number of individuals within a standard 



m 



Sex class 





sampling unit (no. /km) 



T 



Total survey area ( = all statistical subareas 



VAR 



Statistical variance 





combined) 



W 



Observed catch weight (kg) 



V 



Vessel 



a 



Coefficient of length-weight relationship 









(g/cm') 



Symbols 



b 



Exponent of length-weight relationship 



— 



(Over a term) A mean value 





(dimensionless) 



A 



(Over a term) An estimated value 



n 



Number of samples (integer) 



E 





"e 



Number of effective degrees of freedom 



Summation 





(dimensionless) 







