FISHERY BULLETIN: VOL. 81, NO. 3 



one size group to the next was the same, the range of 

 the size groups themselves was different. In biologi- 

 cal terms, this means that there is a significant dif- 

 ference in the size at M 50 for all areas tested. 

 Subsequently, the ages at which Greenland halibut 

 reach the 50% maturity level are also different for 

 these areas. 



DISCUSSION 

 Age and Growth 



Age composition of Greenland halibut varied 

 throughout the range under consideration. It was ap- 

 parent (although not greatly pronounced) from the 

 age distribution that the older fish were propor- 

 tionately more abundant in the more northerly areas 

 and, according to Bowering (1978c), are more abun- 

 dant in deeper waters. The large numbers of young 

 fish in the Baffin Bank area suggest that this area may 

 be a nursery area as indicated by Atkinson et al. 

 (1981). However, the lower numbers of large Green- 

 land halibut in the Baffin Bank survey may also be 

 due to the ineffectiveness of the fishing gear at great 

 depths (>500-700 m), since the vessel is com- 

 paratively small for fishing such depths. Chumakov 

 (1975) found that the oldest individuals throughout 

 the range studied here are located in waters >800 m 

 deep in the northern region of Baffin Island (which he 

 considered to be on or near the spawning grounds). 

 Berth etal. (1979), in reporting results of a survey for 

 Greenland halibut throughout the same area in De- 

 cember 1978, also found that young Greenland hali- 

 but increased in abundance with increased distance 

 from the more northerly areas. Berth 2 also found that 

 mature individuals are more abundant in the more 

 northerly areas, suggesting a northward migration of 

 maturing Greenland halibut for spawning. Subse- 

 quently, Templeman (1973) indicated that pelagic 

 larvae are carried from there by the polar currents to 

 the banks of west Greenland and eastern Canada. 



The absence of Greenland halibut less than age 4 

 from the Gulf of St. Lawrence is difficult to explain. It 

 may be that the young fish move to a different area 

 than that surveyed in winter or, for some unknown 

 reason, they are inaccessible to the fishing gear. It 

 may be possible that if there is immigration into the 

 Gulf of St. LaWrence from outside as suggested by 

 Bowering (1980a, 1981), it may not include Green- 

 land halibut in the very young age groups. The report- 



! U. Berth, Senior Scientist, Institut fur Hochseefischerei and 

 Fischverarbeitung, 251 Rostock-Marienehe, German Democratic 

 Republic, pers. commun. October 1978. 



ing of numerous 1-group Greenland halibut in 

 summer of 1980 by Tremblay and Axelsen (1981) 

 may in fact simply be the result of a very strong 

 anomalous year class produced by a resident popula- 

 tion of Greenland halibut within the Gulf of St. Law- 

 rence. Furthermore, Bowering (in press) indicated 

 that recruitment to the Gulf of St. Lawrence fishery 

 was higher than that which could be expected from 

 the stock of mature fish in the gulf. Therefore, most 

 recruitment would have to come from elsewhere. 

 Evidence from electrophoretic studies (Fairbairn 

 1981) also supports this hypothesis. Fairbairn (1981) 

 concluded that Greenland halibut in the Gulf of St. 

 Lawrence support a separate breeding stock with 

 some gene flow (migration) between the Gulf of St. 

 Lawrence area and the Northeast Newfoundland 

 Shelf area, probably through the Strait of Belle Isle. 

 It would appear then that the Gulf of St. Lawrence 

 Greenland halibut population is composed of a small 

 stock that spawns there and immigrants from the 

 Labrador area that may emigrate to the north for 

 spawning. 



Growth Patterns 



Differences in growth rate between males and fe- 

 males are generally the result of genetics which de- 

 termine the physiology and behavior of the fish 

 rather than the result of the environment (Aim 1959), 

 since the males and females presumably are subject- 

 ed to the same set of environmental conditions. 

 These differences are generally the result of a diver- 

 sion of energy towards the formation of the sex pro- 

 ducts with less energy available for growth, according 

 to Aim (1959). Bowering (1978a) expressed growth 

 of Greenland halibut in terms of linear least squares 

 regression, since most fish in the study were imma- 

 ture and showed little or no diversion in growth pat- 

 terns of males and females. Because of this, it was 

 considered that the study only dealt with that section 

 of the growth curve below the inflection point, and 

 consequently estimates of L„ for the traditional von 

 Bertalanffy growth equation were not realistic and 

 could not be used. Results of back-calculated growth 

 curves up to age 5 in this study resulted in no statisti- 

 cal difference between males and females, which in 

 essence would support Aim (1959) and Bowering 

 (1978a). Furthermore, the mean size-at-age points 

 from the empirical data suggest that the difference 

 in growth patterns between males and females would 

 not be readily observed until in the range of 8-12 yr 

 olds. These data suggest that, with the possible ex- 

 ception of the Gulf of St. Lawrence, the influence of 

 sexual maturity on growth patterns in these areas was 



608 



