NOTE Cooper et al.: Natural mortality rate, annual fecundity, and maturity at lengtti for Reinhardtius hippoglossoides 301 



(mean diameter of vitellogenic oocytes >1000 .um), the 

 mean fraction of atretic vitellogenic oocytes was 0.04 

 (standard deviation [SD] = 0.05, ?i=108). 



Length at maturity 



All females smaller than 65 cm were categorized as 

 immature, although few females were collected between 

 51 and 60 cm (2 females between 61 and 65 cm, and 4 

 females between 56 and 60 cm). All females larger than 

 70 cm were categorized as mature. 



Discussion 



The results from both our study and D'yakov's study 

 (1982) fall within reported ranges of fecundity from 

 other regions; however there is strong variation between 

 the regions in fecundity at length (Fig. 5). Gundersen 

 (2003) hypothesized a geographic variation in fecundity 

 for Greenland halibut. This variation may be caused by 

 a trade-off between egg size and fecundity (Roff, 1992). 

 The largest vitellogenic oocytes before hydration in 

 our study were about 1700 f<m, compared to 2800 fim 

 reported by Gundersen (2003) for samples collected in 

 the Barents Sea. Fecundity estimates by Gundersen 

 (2000) from samples collected in the Barents Sea in 

 1996, 1997, and 1998 were all lower than the fecundity 

 estimates from our study (Fig. 5). 



Maturity at length 



No precise estimate of female length at 50% matu- 

 rity was possible because of a scarcity of collected 

 samples near the presumed length at 50% maturity. 

 The data indicate length at 50% maturity is somewhere 

 between 65 and 70 cm and is higher than the 60 cm 

 value currently used in stock assessment (lanelli et 

 al.M. Estimates for female length at 50% maturity for 

 this species in other geographic regions range from 

 48-80 cm (Table 2). 



Fecundity 



Atresia followed the same general pattern as reported 

 by Gundersen (2003) and did not have a large effect on 

 annual fecundity. Fecundity at length from our study 

 was somewhat higher than that reported by D'yakov 

 (1982) from samples collected in 1978 in the Bering Sea. 



Length-GSI relationship and instantaneous rate 

 of natural mortality 



The estimated rate of instantaneous natural mortality 

 of 0.112 from our study is lower than the value of M cur- 

 rently used in the Bering Sea and Aleutian Islands stock 

 assessment. The stock assessment uses a maximum age 

 of 21 to estimate M to be 0.18 (lanelli et al.M. 



Our estimate for M corresponds more closely with 

 results from Gregg et al. (2006) who aged Greenland 

 halibut from the Bering Sea up to 36 years, corre- 

 sponding to an M of 0.115. A recent age validation 

 study has revealed that Greenland halibut in the At- 

 lantic live up to 33 years, which is also older than 

 previous estimates (Treble et al.^). Overestimating M 

 may result in unsustainably high target harvest rates 

 (Clark, 1999). 



This study provides a length range for estimated 

 length at 50% maturity, annual fecundity, and an 



