264 



Abstract.— A manned submersible 

 was used in the eastern Gulf of Alaska 

 in 1992 to obser\'e spatial distributions 

 and habitats of shortraker rockfish, 

 Sebastes borealis, and rougheye rock- 

 fish, S. aleutianus, on the continental 

 slope at 262-365 m depths. Observa- 

 tions of these two species were com- 

 bined because distinguishing between 

 them was not always possible from the 

 submersible. A seafloor area of 104,900 

 m^ was surveyed at 15 dive sites, and 

 646 shortraker and rougheye rockfish 

 were observed. Densities were 0.0 to 

 14.8 rockfish/1000 m- (mean, 5.8 rock- 

 fish/1000 m-l. Of the 646 rockfish, 115 

 were observed above bottom and 531 

 were on the bottom. The above-bottom 

 rockfish were descending slowly to the 

 seafloor and became sedentary when 

 they contacted the seafloor. Approxi- 

 mately two-thirds of the rockfish were 

 in groups; 82 of the 113 groups con- 

 tained 2 or 3 rockfish. and only 2 groups 

 had more than 12 rockfish. Rockfish 

 were associated w'ith 20 of the 22 sub- 

 strates encountered. Soft substrates of 

 sand or mud usually had the greatest 

 densities of rockfish, whereas hard sub- 

 strates of bedrock, cobble, or pebble 

 usually had the least densities. Habi- 

 tats containing steep slopes and numer- 

 ous boulders had greater densities of 

 rockfish than habitats with gradual 

 slopes and few boulders; 52 rockfish lay 

 against boulders. According to catch 

 rates from bottom-trawl surveys, popu- 

 lations of shortraker and rougheye 

 rockfish may be underestimated be- 

 cause of the above-bottom distribution 

 of these rockfish and their use of steep- 

 slope boulder habitats. 



Distribution and abundance of 

 shortraker rockfish, Sebastes borealis, 

 and rougheye rockfish, S. aleutianus, 

 determined from a manned submersible 



Kenneth J. Krieger 



Auke Bay Laboratory, Alaska Fisheries Science Center 



National Marine Fisheries Service, NOAA 



11305 Glacier Highway 



Juneau, Alaska 99801-8626 



E mail address Ken Kneger g noaa gov 



Daniel H. Ito 



Alaska Fisheries Science Center 

 National Marine Fisheries Service, NOAA 

 7600 Sand Point Way N E 

 Seattle, Washington 98115-0070 



Manuscript accepted 20 May 1998. 

 Fishery Bulletin 97:264-272 (1999). 



Shortraker rockfish, Sebastes borea- 

 lis, and rougheye rockfish, S. aleu- 

 tianus, occur in commercial quanti- 

 ties from northern Washington 

 throughout Alaska (Allen and Smith, 

 1988). Both species are similar in 

 appearance and share similar life- 

 history patterns. These rockfish at- 

 tain maximum total lengths of 

 about 100 cm (Kramer and O'Con- 

 nell, 1986) and have been aged at 

 more than 120 years (Chilton and 

 Beamish, 1982). Their bathynietric 

 range is 25-875 m (Allen and Smith, 

 1988), and their lengths at 50^, ma- 

 turity are 43.97 cm for rougheye rock- 

 fish and 44.90 cm for shortraker rock- 

 fish (McDermott, 1994). They appar- 

 ently share similar habitats. During 

 the 1996 Gulf of Alaska triennial sur- 

 vey, 89*^ of the trawl hauls contain- 

 ing shortraker rockfish also contained 

 rougheye rockfish. 



Shortraker and rougheye rockfish 

 are harvested with bottom trawls 

 and longlines in the Gulf of Alaska. 

 Until the mid 1980s, they were 

 mainly bycatch species caught dur- 

 ing longlining for halibut, Hippo- 

 glossus steiwlepis, and sablefish, 

 Anoplopoma fimbria, and during 

 bottom trawling for more abundant 



rockfish species. Before 1991, 

 shortraker and rougheye rockfish 

 were combined with 18 other rock- 

 fish species and managed as "slope 

 rockfish." Since 1991, shortraker 

 and rougheye rockfish have been 

 managed as a separate subgroup 

 because fishermen target these 

 highly valued species. For example, 

 shortraker and rougheye rockfish 

 made up 337f of the commercial 

 rockfish catch in the eastern Gulf 

 of Alaska in 1990 but made up only 

 14*7^ of the estimated rockfish bio- 

 mass (Heifetz and Clausen, 1991). 

 Catch quotas of shortraker and 

 rougheye rockfish are based prima- 

 rily on population estimates derived 

 from catch rates of bottom-trawl 

 surveys ( Heifetz etal., 1996). These 

 estimates are suspect because the 

 catch efficiency of bottom trawls on 

 these species is unknown and only 

 certain types of habitats can be 

 sampled with bottom trawls. 



Catch rates from bottom-trawl sur- 

 veys are converted to biomass esti- 

 mates by assuming a 100'^ sampling 

 efficiency for the area swept by the 

 trawl. The area that is swept is de- 

 termined as the distance between the 

 wingtips of the net and the distance 



