914 
Fishery Bulletin 96(4), 1998 
Table 1 
Comparison of parasite prevalence (proportion of fish having the parasite) by area for shortraker and rougheye rockfish in the 
Gulf of Alaska, 1990. The number of fish examined in each area is given in parentheses. Significance probability is given for a 
categorical analysis of variance model with area and fish size as main effects. Asterisks indicate P < 0.10. 
Parasite prevalence 
Significance 
probability 
Shumagin 
Chirikof 
Kodiak 
Yakutat 
Southeast 
Area 
Size 
Shortraker rockfish 
(n=21) 
(72 = 20) 
(77=20) 
o 
CM 
II 
(77=20) 
Neobrachiella robusta 
0.48 
0.55 
0.80 
0.35 
0.40 
0.076* 
0.724 
Naobranchia occidentalis 
0.00 
0.10 
0.10 
0.10 
0.00 
0.980 
0.493 
Chondracanthus pinguis 
0.10 
0.05 
0.10 
0.10 
0.10 
0.971 
0.301 
Colobomatus kyphosus 
0.00 
0.00 
0.00 
0.05 
0.00 
0.954 
0.583 
Trochopus trituba 
0.62 
0.60 
0.86 
0.55 
0.45 
0.081* 
0.262 
Microcotyle sebastis 
0.14 
0.10 
0.00 
0.00 
0.00 
0.927 
0.655 
Corynosoma sp. 
0.81 
0.75 
0.60 
0.65 
0.65 
0.606 
0.914 
Echinorhynchus gadi 
0.10 
0.00 
0.00 
0.05 
0.00 
0.929 
0.633 
Clavella parva 
0.62 
0.80 
0.90 
0.30 
0.20 
0.013* 
0.370 
Rougheye rockfish 
(72=20) 
O 
CM 
II 
(77 = 20) 
(77=20) 
(77=20) 
Neobrachiella robusta 
0.25 
0.40 
0.30 
0.50 
0.10 
0.087* 
0.028* 
Naobranchia occidentalis 
0.00 
0.00 
0.00 
0.20 
0.00 
0.897 
0.823 
Chondracanthus pinguis 
0.10 
0.00 
0.00 
0.40 
0.50 
0.152 
0.069* 
Colobomatus kyphosus 
0.00 
0.00 
0.00 
0.10 
0.10 
0.960 
0.165 
Trochopus trituba 
0.70 
0.60 
0.55 
0.50 
0.20 
0.045* 
0.822 
Microcotyle sebastis 
0.15 
0.00 
0.00 
0.15 
0.00 
0.906 
0.895 
Corynosoma sp. 
0.80 
0.75 
0.75 
0.75 
0.20 
0.001* 
0.283 
Echinorhynchus gadi 
0.00 
0.00 
0.15 
0.00 
0.05 
0.674 
0.356 
Clavella parva 
0.48 
0.10 
0.10 
0.70 
0.55 
0.105 
0.704 
cosus, a common parasite in the nasal cavities of 
Canadian rockfishes, was largely absent from our 
samples, occurring in only a single specimen. The 
fin copepod Clavella parva was present in all areas, 
with increased prevalence among shortraker rock- 
fish in the western GOA; this difference was signifi- 
cant (P=0.013) between areas. Although we exam- 
ined all parasites in our sample, C. parva was never 
a candidate for separation, because fin parasites 
could be lost in capture and sampling. 
The parasites showing the most potential for pro- 
viding insights into the population structure for both 
species of rockfishes were the monogenetic trema- 
todes T. trituba and Microcotyle sebastis, because of 
their high and low prevalences, respectively. Preva- 
lence and intensity of T. trituba were significantly 
lower for rougheye rockfish in the Southeast (20% 
prevalence, mean intensity of 1.8) than in other man- 
agement areas (50-70% prevalence, mean intensity 
of 2-9). For shortraker rockfish, prevalence and in- 
tensity of T. trituba were highest in Kodiak (86%, 
intensity of 16) and declined farther southward (45% 
and 8 in the Southeast, 62% and 4 in Shumagin). 
Both prevalence and intensities of T. trituba differed 
significantly among areas and did not depend on fish 
size. Microcotyle sebastis, common among many spe- 
cies of British Columbia rockfishes, was rare in the 
GOA. 
The only internal parasite showing potential as a 
tag was Corynosoma sp., which, with the less com- 
mon acanthocephalan Echinorhynchus gadi, infected 
nearly every Shumagin shortraker rockfish (90% in- 
fected with an acanthocephalan at an average of 
three Corynosoma sp. per fish). Most other shortraker 
rockfish were also infected (60-75%). Although 
prevalences of Corynosoma sp. in shortraker rock- 
fish did not differ among areas, intensities and in- 
tensities/cm differed significantly (P=0.024 and 
0.019, respectively) by area, largely owing to high 
numbers of Corynosoma sp. among Yakutat fish. 
Rougheye rockfish were also infected with Cory- 
nosoma sp. at 75-80%, except in the Southeast (20%; 
significantly lower [P=0.001] than in other areas). 
Discussion 
Williams et al. (1992) proposed six criteria to assess 
the value of a parasite as a marker for stock separa- 
tion. The parasite should differ in levels of infection 
across geographic regions, not be detached easily with 
handling, be easily assessed, have no harmful effect 
