766 



Fishery Bulletin 88(4), 1990 



Figure 5 



Response surface of the SRLCA score function for the northern 

 shrimp survey 1985 length-frequency distribution. 



of assumed age-3 shrimp in the two subsequent years, 

 suggests that the 1982 YC may also have experienced 

 a slower growth rate between ages 2 and 3 than 

 preceding cohorts. 



The highest value in the SRLCA primary score ridge 

 was at L„,i- = 35 mm, K = 0.48, with the ridge then 

 continuing to L|„f = 50 mm, K = 0.21. Parameters in 

 this primary ridge classified the first two modes as suc- 

 cessive cohorts, with three age groups total. A second- 

 ary ridge, from L,nf = 42 mm, K = 0.50 to a boundary 

 maximum at Linf = 50 mm, K = 0.34, resolved the 

 distribution to only two age groups, with modal lengths 

 of 17.0 and 26.5 mm for ages 1 and 2. It was necessary 

 to explore a tertiary ridge, with a nonboundary local 

 maximum at L|„, = 29 mm. K = 0.42, to successfully in- 

 terpret the first two length modes as age groups 1 and 

 3, with shrimp >24.5 mm resolved to two main age- 

 groups (Table 2; Fig. 5, 6). 



o 



< 



UJ 

 Q 



1985 



1982 YC 

 AGE 3 



fin 



i 



.' 



ft/^ 



Jin 



Ww^ 



10 15 20 25 30 



CARAPACE LENGTH (mm) 



80 



35 



h40 ^ 

 O 



o 

 (/) 



> 



_i 

 2 



n 



h-20 ^ 



Figure 6 



Northern shrimp survey 1985 length-frequency distribution (histo- 

 gram) and pattern of SRLCA scores (solid curve) for growth param- 

 eters selected for final evaluation (L,„, = 29 mm, K = 0.42). 



1 986 distribution This distribution is characterized 

 l)y three clearly defined modes at 13-18 mm, 19-22 

 mm, and >25 mm, assumed to be ages 1, 2, and 4, and 

 a small mode at 23 mm assumed to be either the 1983 

 cohort at age 3 or slow-growing shrimp from the 1982 

 cohort at age 4 (NSTC 1986; Fig. 2). Two ridges of com- 

 parable high scores were apparent from an initial 

 SRLCA run, a primary ridge from L,,,)- = 35 mm, K = 



0.49 to a boundary maximum at L,,,! = 50 mni, K = 

 0.22, and a secondary ridge from Linf = 32 mm. K = 

 0.47 to L,nf = 40 mm," K = 0.23 (Table 3, Fig. 7). The 

 primary ridge identified three modal groups, matching 

 the first observed mode well, but classifying shrimp 

 between 18.5 and 24.5 mm as a single group, with the 



