Abookire Biology, spawning season, and growth of Glyptocephalus zachirus 



351 



the trawl flatfish fishery once the allowed 

 limit of Pacific halibut bycatch is captured 

 (DiCosimo and KimbalH). 



The life history, reproductive biology, and 

 growth of rex sole were investigated off the 

 Oregon coast from 1969 to 1973 (Hosie and 

 Horton, 1977). Despite the wide geographic 

 range of rex sole, no investigations have oc- 

 curred elsewhere. Although rex sole in the 

 GOA are managed as a single species unit 

 with species-specific assessments of biomass 

 and ABC estimates, there is no information 

 on length or age at maturity to incorporate 

 into analytical stock assessments. Thus, there 

 is a substantial need for obtaining informa- 

 tion on the reproductive biology of rex sole 

 in the GOA for the purpose of stock-specific 

 assessment and management. 



To clarify the seasonal maturation dynam- 

 ics and reproductive biology of female rex sole 

 in the GOA, fish were collected year-round 

 and their ovaries were analyzed by using 

 standard histological techniques. To date, 

 there have been no histological investigations 

 on rex sole maturity (Castillo, 1995). Specific 

 goals of this investigation were to determine 

 the spawning season, length at first maturity, 

 length at 50% maturity (MLgj,). age at first 

 maturity, and age at 50'7f maturity (MAr,,,). 

 Additionally, inasmuch as possible, reproduc- 

 tive parameters and growth were compared 

 between female rex sole in the GOA with 

 those off the Oregon coast (data from Hosie 

 and Horton, 1977). Reproductive parameters 

 determined in this study will aid the develop- 

 ment of a species-specific assessment of target fishing 

 mortality rates and mature female biomass. yielding a 

 more accurate management model for the GOA stock 

 of rex sole. 



Materials and methods 



6aN 



-I- 



: Commercial trawls 

 + Research trawls 



30 60 120 



55 N 



s 



Collections 



Rex sole were collected from 14 February 2000 to 

 21 October 2001 in the central GOA (from 55°30'N, 

 156°00'W to 59°50'N, 147°15'W; Fig. 1). Approximately 

 half (52% ) of the samples were collected at fish process- 

 ing plants in Kodiak, Alaska. The shore-side sampling 

 data were dependent on the timing of the fishery, but 

 allowed for the annual cycle of sexual maturation to be 

 monitored. Shore-side sampling occurred in January, 

 February, April, May, October, November, and December, 

 and samples were obtained from boats that captured rex 

 sole as bycatch while fishing for other species. Although 

 there is no inherent biological difference in rex sole col- 

 lected by commercial or research trawl, typically samples 

 from the commercial fishery exclude young fish that are 

 below the minimum landing size or escape through the 



Figure 1 



Collections of female rex sole (Glyptocephalus zachirus) in the Gulf of 

 Alaska were concentrated around Kodiak Island, Alaska. Samples were 

 obtained from the commercial trawl fishery (denoted by open circles) and 

 from research survey trawls (denoted by crosses). 



meshes. However, because of the close proximity of the 

 fishing grounds to the town of Kodiak, catches were not 

 sorted at sea and very small rex sole (minimum total 

 length [TL] = 172 mm) were brought back to the pro- 

 cessing plants where they were obtained for this study. 

 The remaining 48% of samples were collected during 

 research surveys in February, March, June, and July 

 by the National Marine Fisheries Service (NMFS) and 

 the University of Alaska Fairbanks with smaller-meshed 

 trawls in the same waters fished by the commercial 

 fishery. 



Samples were stratified by length, so that up to five 

 females per 1-cm length group were obtained each 

 month. For each female, total length (to the nearest 

 mm) and weight (to the nearest 0.1 gram) were mea- 

 sured, both sagittal otoliths were removed, and ovarian 

 maturity was macroscopically staged. Each ovary was 

 removed and weighed separately (to the nearest 0.1 

 gram). Ovaries were preserved in 10%^ buffered forma- 

 lin for 2 months and then transferred to 70%j ethanol. 

 All ovaries collected at sea were weighed only after 

 preservation; ovaries collected at processing plants were 

 weighed both when fresh and after preservation. 



Sagittal otoliths were removed from each fish, stored 

 in a glycerol and thymol solution, and most (n = 557) 



