Fruh et al.: Accuracy of sex determination for Sebastolobus altivelis and 5. alascanus 
229 
Table 1 
Number ( n ), mean fork length (cm, ±standard error [SE] ), and analyses of variance (ANOVAs) for sizes for female, male, and 
total longspine ( Sebastolobus altivelis) and for female, male, and total shortspine thornyheads ( S . alascanus) captured during 
the 2003 Northwest Fisheries Science Center west coast groundfish trawl survey, correctly and incorrectly assigned sex based 
on visual examination. 
Correct 
Incorrect 
ANOVAs 
Species 
n 
Mean length ( ± SE ) 
n 
Mean length ( ± SE ) 
df 
F 
P 
Longspine thornyhead 
female 
396 
21.6 (0.21) 
114 
18.5 (0.37) 
509 
48.9 
0.0001 
male 
259 
23.4 (0.20) 
83 
19.0 (0.47) 
341 
96.6 
0.0001 
total 
655 
22.3 (0.15) 
197 
18.7 (0.29) 
851 
52.7 
0.0001 
Shortspine thornyhead 
female 
560 
35.5 (0.52) 
58 
23.6 (1.16) 
617 
50.8 
0.0001 
male 
481 
34.9 (0.45) 
49 
28.1 (1.52) 
529 
21.5 
0.0001 
total 
1041 
35.2 (0.35) 
107 
25.7 (0.96) 
1147 
36.2 
0.0001 
above 43°N latitude, and the U.S. -Vancouver and Co- 
lumbia areas had a significantly higher average per- 
centage of misidentification than the Eureka, Monterey, 
and Conception areas (ANOVA: df=4, F=44.1, P-0.007). 
The sex of shortspine thornyheads became more diffi- 
cult to correctly identify below 40°N latitude, and both 
the Monterey and Conception areas had a significantly 
higher average percentage of misidentification com- 
pared to the Eureka, Columbia, and U.S. -Vancouver 
areas (ANOVA: df=4, P=13.9, P=0.03). There were no 
