Hawkins et al : Genetic variation of Sebastes aleutianus and S. boreahs 



533 



The initial objective of our study did not include col- 

 lection of morphological data, but in light of the genetic 

 differences detected, and the color morphs detected by 

 Seeb (1986), morphology of the two lineages should be 

 more closely examined. Upon processing the 2001 fish, 

 we noted that many were easily identified as either light 

 or dark in color, although some appeared intermediate. 

 The obvious light-colored individuals were all found 

 genetically to be S. aleutianus, whereas the darker 

 specimens were typically Sebastes sp. cf. aleutianus. 

 Although Tsuyuki and Westrheim (1970) reported no 

 distinguishing meristic or morphometric characters 

 between S. aleutianus blood types, Seeb (1986) sepa- 

 rated rougheye rockfish morphologically and by color 

 into two groups: one that was light pink and had spines 

 under the orbit of the eye (S. aleutianus); the other 

 was darker and had a considerable area of black on the 

 mouth and jaw and often lacked orbital spines (S. aleu- 

 tianus unknown). The lack of orbital spines in Sebastes 

 sp. cf. aleutianus is an important observation because 

 this feature is a key characteristic in distinguishing 

 S. aleutianus from S. borealis. 



Initial observations of the distribution of the 1993 

 rougheye samples displayed a pattern of predominately 

 S. aleutianus in the Gulf of Alaska and almost entirely 

 S. sp. cf. aleutianus in the Aleutian Islands. A parasite 

 study (Moles et al., 1998) performed on the same rough- 

 eye rockfish reported a significantly greater (P<0.05) 

 prevalence of three parasites in the Aleutian Island 

 samples. Upon close examination of the depth of the 

 sample collection, we noted that the Aleutian Islands 

 samples were collected in deeper waters than those col- 

 lected in the Gulf of Alaska. Thus subsequent sampling 

 strategies focused on a possible depth niche. Parasite 

 data from both the shallow and deep water 2001 rough- 

 eye collections showed a significant prevalence of two 

 parasites in the deeper host, Sebastes sp. cf. aleutianus 

 (Table 5). The prevalence of the parasite T. trituba may 

 be dependent on host habitat. Because the hosts (two 

 aleutianus types) exhibited significantly different preva- 

 lences of the parasite T. tributa, they may be using 

 different resources (different diets) and (or) exhibiting 

 ecological segregation (Moles et al., 1998). 



Both Sebastes aleutianus types are found in the Gulf 

 of Alaska and occur in sympatry, although the majority 

 of S. sp. cf. aleutianus are distributed at deeper depths 

 (Fig. 3). Bathymetric segregation has been noted in 

 other closely related rockfish. Sebastes fasciatus and 

 Sebastes mentella in the Atlantic Ocean elude abun- 

 dance estimates because of a lack of easily identifiable 

 morphological characteristics. In the laboratory, these 

 two species are nearly fixed at alternate alleles at the 

 allozyme locus MDH*. A bathymetric segregation is de- 

 tected, where S. fasciatus is found at depths of 132-315 

 m, S. mentella at depths greater than 355 m, and both 

 species and possible hybrids at intermediate depths (Ru- 

 bec et al., 1991). Another species pair, Sebastes carnatus 

 and Sebastes chrysomelas, are both shallow-dwelling 

 species (depth less than 20 m) that coexist only in a 

 narrow zone of overlap that separates exclusive depth 



ranges. Factors organizing their segregation are largely 

 behavioral because both species expand their depths in 

 the absence of the other species (Larson, 1980). Rough- 

 eye rockfish may exhibit a similar strategy. Deep sam- 

 pling efforts near Washington state have indicated that 

 the distribution of S. sp. cf. aleutianus may diminish 

 in southern ranges and it appears that the distribu- 

 tion of S. aleutianus does not extend to the western 

 Aleutian Islands and Asia. This pattern of distribution 

 has been noted in other closely related species, such as 

 the northern and southern species of Lepidopsetta (Orr 

 and Matarese, 2000). The poorly understood ontogenetic 

 and seasonal movements of rougheye and other rockfish 

 further confound the picture. For example, S. altivelis 

 and S. alascanus were long thought to be deep-dwelling 

 and shallow-dwelling congeneric species, respectively. It 

 is now known that S. altivelis is a permanent deepwater 

 resident, whereas S. alascanus settles in shallow water, 

 then migrates to deep water with the onset of sexual 

 maturity. Competition between these two species may 

 be reduced by size differences; for example, where they 

 are sympatric, S. alascanus is much larger than S. al- 

 tivelis (Vetter and Lynn, 1997). Although length data 

 for rougheye rockfish in sympatry are limited, a single 

 haul (n=29) near Dixon Entrance (depth of capture= 

 213 m) yielded both types, and nearly all the S. aleutia- 

 nus individuals were much larger (mean 56.3 cm) than 

 Sebastes sp. cf. aleutianus (mean 37.2 cm). No age data 

 are currently available to add insight into these results. 

 The trend of smaller fish in shallower waters and larger 

 fish in deeper waters was significant for S. aleutianus in 

 the Gulf of Alaska. This was not detected for Sebastes 

 sp. cf. aleutianus, although their full depth range may 

 not have been sampled. Perhaps only younger Sebastes 

 sp. cf. aleutianus were collected, and the older, larger 

 fish are deeper and remain unsampled. It would be ben- 

 eficial to analyze juvenile rougheye rockfish to ascertain 

 genetic type composition at different depths. 



A significant size difference existed between fish 

 in the Gulf of Alaska and those of the Aleutian Is- 

 lands, especially among shortraker rockfish. Aleutian 

 fish were smaller, despite collection at greater depth. 

 Growth and age of maturation differences among dif- 

 fering latitudes and longitudes have been noted in 

 other rockfish species (Westrheim, 1973; Archibald et 

 al., 1981; Field, 1984; Lunsford, 1999). The size differ- 

 ence among shortraker rockfish has been previously 

 noted (Orlov, 2001; Matala, 2004) and raises more 

 questions than it answers. It is still unknown whether 

 these differences are caused by different age classes or 

 regional ecological differences. 



Allozyme data did not reveal heterogeneity within 

 either rougheye rockfish type or within shortraker rock- 

 fish throughout the sampled geographic range. Although 

 no heterogeneity was detected with our suite of allozyme 

 loci, other genetic markers, such as microsatellite loci, 

 may provide finer resolution of population structure. 

 A recent study of shortraker microsatellite variation 

 revealed geographically restricted homogeneity among 

 allele frequencies — a model consistent with the assump- 



