320 
Fishery Bulletin 99(2) 
Table 6 
Average depth distributions, i.e. probabilities of depth given length or p(d \ L), and CVs for male and female Dover sole between 
36°00'N and 48°30'N Lat and between 100 and 699 fm during October-December based on eight National Marine Fisheries Service 
bottom trawl surveys. Length groups and depth intervals defined as in Table 5. All eight surveys took 20-44 cm male and female 
Dover sole. The symbol “ — “ means that CV could not be calculated because the average depth distribution was zero. 
Depth intervals (fm) 
Total length (cm) 
100-199 
200-299 
300-399 
400-499 
500-599 
600-699 
Depth distributions (males) 
20 
0.5616 
0.4333 
0.0051 
0.0000 
0.0000 
0.0000 
22 
0.5479 
0.4491 
0.0031 
0.0000 
0.0000 
0.0000 
24 
0.5018 
0.4928 
0.0053 
0.0000 
0.0000 
0.0000 
26 
0.4652 
0.5256 
0.0080 
0.0010 
0.0001 
0.0000 
28 
0.4116 
0.5664 
0.0185 
0.0033 
0.0003 
0.0000 
30 
0.3212 
0.6225 
0.0447 
0.0111 
0.0006 
0.0000 
32 
0.2412 
0.6175 
0.0956 
0.0392 
0.0065 
0.0000 
34 
0.1565 
0.5560 
0.1802 
0.0859 
0.0201 
0.0014 
36 
0.0916 
0.4552 
0.2575 
0.1394 
0.0472 
0.0092 
38 
0.0506 
0.2654 
0.3139 
0.2052 
0.1444 
0.0205 
40 
0.0174 
0.1560 
0.3527 
0.2276 
0.1916 
0.0548 
42 
0.0046 
0.1248 
0.3282 
0.2167 
0.1951 
0.1305 
44 
0.0041 
0.1239 
0.3592 
0.1859 
0.1497 
0.1772 
CV (males) 
20 
0.20 
0.27 
1.00 
— 
— 
— 
22 
0.20 
0.24 
0.87 
— 
— 
— 
24 
0.16 
0.16 
0.57 
— 
— 
— 
26 
0.18 
0.15 
0.51 
0.66 
1.00 
— 
28 
0.18 
0.13 
0.27 
0.58 
1.00 
— 
30 
0.20 
0.10 
0.24 
0.29 
0.57 
— 
32 
0.20 
0.08 
0.19 
0.39 
0.43 
— 
34 
0.24 
0.09 
0.18 
0.35 
0.40 
0.52 
36 
0.28 
0.15 
0.19 
0.22 
0.28 
0.33 
38 
0.36 
0.21 
0.08 
0.18 
0.24 
0.13 
40 
0.39 
0.33 
0.07 
0.14 
0.21 
0.20 
42 
0.56 
0.21 
0.07 
0.18 
0.22 
0.25 
44 
0.66 
0.28 
0.10 
0.22 
0.22 
0.23 
contin ued 
curves resemble the underlying vulnerability curves. These 
results imply that temporal changes in the right-hand side 
of the curve should be of greatest concern to stock assess- 
ment scientists. 
Commercial bottom trawl selectivities for large long- 
spine thornyhead may have increased slightly over time 
as the fishery moved into deeper water (Fig. 9). This re- 
sult implies a small amount of ontogenetic migration in 
longspine thornyhead not evident in our length-specific 
depth distributions (Fig. 5). Selectivity calculations, which 
are based on the full suite of depth distributions and fish- 
ing effort data, may be a more sensitive indicator of on- 
togenetic migration patterns not clearly visible in plots 
showing length-specific depth distributions for longspine 
thornyhead. It is also possible that the hint of ontogenetic 
migration in longspine thornyhead was due to estimation 
errors in depth distributions, lack of species-specific vul- 
nerability parameters, or other factors. 
As described above, differences between sexes in length- 
specific commercial bottom trawl selectivities were minor. 
This implies little need for sex-specific selectivity parame- 
ters in stock assessment models if selectivity is calculated as 
a function of length. If selectivity is modeled as a function 
of age, and growth rates of males and females are different 
(often the case for west coast groundfish), then sex-specific 
selectivity parameters may be required. Sex-specific length- 
based selectivity parameters would be required if ontogenet- 
ic migration is more closely related to age than length. 
Clear trends in our fishery selectivity estimates for com- 
mercial bottom trawls suggest a reasonable level of preci- 
