FISHERY BULLETIN: VOL. 81, NO. 3 



combined for each of the areas for further analysis. A 

 covariance analysis was performed on these com- 

 bined data to determine if there were any significant 

 differences in the slopes of the fitted lines. Among 

 the different areas, for areas where significant dif- 

 ferences did not occur, the analysis was continued by 

 using paired comparisons by f-tests to determine if 

 differences occurred between the adjusted means (y- 

 intercepts). 



Sexual Maturity 



Due to the difficulty and uncertainty connected 

 with the determination of sexual maturity in male 

 Greenland halibut, only sexual maturity data on fe- 

 male Greenland halibut were analyzed. Except for 

 the Gulf of St. Lawrence data, only data collected 

 during the same time of year were used to generate 

 the maturity curves. Maturity conditions were deter- 

 mined by visual observations made at sea. Fish were 

 considered mature if primary ova were visible in the 

 ovary at any stage or if fish were in spawning or 

 postspawning stages; otherwise, fish were con- 

 sidered immature. 



The age or length when equal numbers of fish are 

 mature and immature is known as the 50% maturity 

 level or more commonly M, . In assessing the effects 

 of various dosages of poisons and vitamins on ani- 

 mals, Bliss (1952) devised a probit analysis method 

 for calculating the 50% lethal dosage level (LD 50 ) 

 which is the level where 50% of the animals are dead. 

 Fleming(1960),Pitt(1966),andBowering(1976) ap- 

 plied the same probit analysis method to determine 

 the length at 50% maturity for cod, American plaice, 

 and witch flounder, respectively. The only difference 

 was that in fitting the provisional line (Bliss 1952), a 

 closer fit was obtained by using log dosages which in 

 the latter studies were the percentages of mature fish 

 plotted against log length on probability paper. This 

 modified probit analysis method was applied to the 

 female Greenland halibut sexual maturity data from 

 each of six areas where data were available. Since 

 sexual maturity data for the northern Grand Bank 

 area were so sparse, these were not included. 



RESULTS 



Age and Growth 



Age Composition 



Age composition of Greenland halibut from Baffin 

 Bank in October 1977 showed a predominance of 

 younger age- groups, particularly 3-5 yr olds, for both 



males and females (Fig. 2). Although fish were pres- 

 ent in the catches up to age 14 for males and age 18 

 for females, very few fish were present beyond 8 yr 

 old. In the Saglek Bank area, the opposite was the 

 case with a strong predominance of fish beyond 5 yr 

 old, although fish in the range of 3-5 yr olds were well 

 represented (Fig. 2). Proportionally, there was a 

 declining trend in the age-9+ groups of males from 

 Saglek Bank to the northern Grand Bank with a 

 marginal decline in the proportion of age- 12+ fe- 

 males from Nain Bank to the northern Grand Bank. 

 The most evident change in age composition over 

 this range, however, is the abrupt change from the 

 Northeast Newfoundland Shelf to the northern 

 Grand Bank, particularly at ages 1 and 2. Age com- 

 positions for the Gulf of St. Lawrence data indicated 

 very few fish less than age 4 for either sex (Fig. 2) with 

 males absent beyond age 10 and females absent be- 

 yond age 12. The predominant age groups were 5-7 yr 

 olds for males and 6-9 yr olds for females, all year 

 classes of the early 1970's. It should be pointed out 

 that since the Gulf of St. Lawrence data were collect- 

 ed in January and all other data collected late in the 

 year, for comparison purposes, the Gulf of St. Law- 

 rence data should be adjusted back by 1 yr. 



Growth Curves from Observed Data 



Female Greenland halibut have a longer life span 

 than male Greenland halibut (Fig. 3). The difference 

 in maximum age between males and females ranged 

 from 2 yr in the Gulf of St. Lawrence to as much as 8 yr 

 in the Saglek Bank area. It would appear from the 

 curves (without considering mean size at age) that for 

 all areas the overall growth rate of females is greater 

 than that of the males. While the curves do not ap- 

 pear to fit the mean data points very well because of 

 the weighting procedure, the correlation coefficients 

 (r) were all greater than r = 0.92 and were all highly 

 significant (P > 0.001). In almost all cases, however, 

 the mean data points for the older ages are above the 

 fitted lines (Fig. 3). This would suggest that if the ob- 

 servations were more numerous in the older ages, the 

 computed growth rates would probably be higher 

 than appear here, since more weight would be given 

 to these points. As a consequence, the predicted size at 

 age is probably only meaningful up to age 7 for males 

 and age 10 for females. Beyond these ages, the mean 

 size at age is increasingly higher than that deter- 

 mined from the fitted lines. In addition, the growth of 

 males and females is identical up to age 7 for some 

 areas and up to age 10 in others. It is clear that the 

 weighting procedure underestimates relationships 

 derived from the regression analyses compared with 



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