NOTE Cooper et al.: Natural mortality rate, annual fecundity, and maturity at length for Reinhardtius hippoglossoides 



297 



Each slide was analyzed for the oocyte stages present 

 and for postovulatory follicles (POFs) according to the 

 descriptions and images from Gundersen (2003) (Fig. 2). 

 Maturity stages were assigned according to Gundersen 

 et al. (2003). 



Length-GSI relationship and 

 instantaneous rate of natural mortality 



For the GSI-M relationship, Gunderson (1997) defined 

 GSI as the point in ovarian development when the ova- 

 ries had attained maximum weight due to vitellogen- 

 esis, but had not gained nonenergetic weight (due to 

 hydration). For this study, fish with ovaries in maturity 

 stage vitellogenesis 4 (Fig. 2) were used in the GSI-M 

 estimate. Fish with ovaries containing hydrated oocytes 

 or POFs were excluded. Fedorov (1968) found that dry 

 weights of oocytes corresponding to the vitellogenesis-4 

 stage (yolk-filled oocyte in the trophoplasmic growth 

 stage) were equal to dry weights of hydrated ova; this 

 result indicates that yolk deposition is completed at the 

 vitellogenesis-4 stage. 



The length of the average mature female in an un- 

 exploited population is required for Gunderson's (1997) 

 GSI-M relationship. The foreign trawl fishery prior to 

 1988 showed the best selectivity for fish in the widest 

 size range (lanelli and Wilderbuer''). Foreign trawl fish- 

 ery data from the NMFS Observer program (Berger^) 

 were analyzed, and the oldest complete data set (1977- 

 87) was chosen to best approximate the true nature of 

 the Greenland halibut population in the absence of fish- 

 ing pressure. The mean length of mature females was 

 determined from the weighted length by using data on 

 the abundance at each length as weights. 



Potential annual fecundity 



To test for homogeneity of vitellogenic oocyte density 

 throughout the ovaries, subsamples were selected from 

 nine fish at three locations (anterior, middle, and pos- 

 terior) on each ovary lobe (eyed side and blind side) 

 for a total of six subsamples per fish. Cross sections 

 were taken through the ovary and included the ovar- 

 ian wall. For the anterior and middle sections, one half 

 of the cross section was used as the subsample. The 

 posterior cross sections of the ovary were much smaller 

 and therefore the entire cross section was used. The 

 subsamples had a mean weight of 2.07 grams (standard 

 error [SE] = 0.14) and a mean number of 553 vitellogenic 



3 lanelli, J. N., and K. T. Wilderbuer. 1995. Greenland 

 turbot (Reinhardtius hippoglossoides) stock assessment and 

 management in the Eastern Bering Sea. In Proceedings of 

 the International Symposium on North Pacific flatfish, p. 

 407-441. Alaska Sea Grant report 95-04. Univ. Alaska 

 Sea Grant College Program, P. O. Box 755040, Fairbanks, 

 AK 99775. 



* Berger, J. 2002. Personal commun. Alaska Fisheries 

 Science Center, National Marine Fisheries Service, 7600 

 Sand Point Way NE, Seattle, WA 98115. 



180 ffo i'l ■:":■ ;. isoo'O'W 



Figure 1 



Map of locations where Greenland halibut (Reinhard- 

 tius hippoglossoides) were collected for ovary samples. 

 Open circles mark locations where fish were collected 

 for the ovary samples. Filled circles mark locations 

 where fish were collected for the natural mortality 

 (M) estimate. 



oocytes (SE = 43.11). Oocyte density (number of oocytes/ 

 gram of ovarian tissue) and diameters of 50 of the most 

 advanced oocytes per fish were recorded. 



Two-way ANOVAs were used to test for differences 

 in oocyte density and diameter between ovarian lobes 

 and among ovarian locations. Paired f-tests were used 

 to identify differences among ovarian locations when 

 the ANOVA detected significant differences. 



Greenland halibut are reported to have determinate 

 fecundity (Gundersen et al., 2001; Junquera et al.. 



