BOWERING: AGE, GROWTH, AND MATURITY OF GREENLAND HALIBUT 



negligible. Statistical comparisons could not be 

 made with Bowering (1978a), since the data could 

 not be standardized. 



Covariance analyses on the back- calculated growth 

 data indicated that the growth rate throughout the 

 entire area, with the exception of the most northerly 

 Baffin Bank area, was the same. The growth rate from 

 the Baffin Bank data was considerably lower than all 

 other areas. Analysis of the adjusted means (inter- 

 cepts) indicated that the average size at age for the 

 Gulf of St. Lawrence data was significantly higher 

 than all other areas. Since the overall growth rate was 

 the same as other areas, this would imply that the 

 growth rate of the Gulf of St. Lawrence fish was sub- 

 stantially higher in the first year of life compared with 

 other areas. While the size at age from Nain Bank was 

 significantly different from all areas, it did not appear 

 to vary greatly from the adjacent Labrador and east- 

 ern Newfoundland areas. Since differences between 

 growth patterns from Saglek Bank and other areas 

 are not totally variable, they may be a result of the 

 location and behavior of the fish in the first year of life 

 throughout the range. 



Because there appears to be a general increase in 

 average size at age from north to south, temperature 

 would appear to be a contributing factor. Temple- 

 man (1964) indicated that the volume of warmer 

 waters increased from north to south because of the 

 direction of the Labrador Current so that tempera- 

 ture may have an influence on growth pattern. Any in- 

 fluence would have to be particularly related to the 

 first year of life, since older Greenland halibut are 

 known to migrate over long distances (Nizovtsev 

 1970; Chumakov 1970; Sigurdsson 1977), as well as 

 vertically in the water column (Lear 1970; de Groot 

 1970), making them subject to a wide variety of tem- 

 peratures. This may explain the high growth rate in 

 the first year for the Gulf of St. Lawrence fish where 

 temperatures are considerably higher than the east- 

 ern areas. It should be pointed out, however, that 

 these growth patterns are based mostly upon imma- 

 ture individuals, and the difference in growth pat- 

 terns of the immature individuals alone may simply 

 be a result of conditions where they grew prior to 

 maturity. Upon approaching maturity they could all 

 still return to a common breeding area and be part of 

 the same original stock. 



Sexual Maturity 



The commercial fisheries for Greenland halibut on 

 the banks and slopes in the northwest Atlantic are 

 mainly composed of immature fish (Chumakov 1975; 

 Zilanov et al. 1976; Templeman 1973; Berth et al. 



1979; Bowering 1977-81). The scarcity of mature 

 fish in the commercial, as well as research, catches 

 led to consideration of the possible misinterpretation 

 of maturity condition of the ovaries, particularly by 

 visual observation. Walsh and Bowering (1981) stud- 

 ied the problem histologically and concluded that 

 while the accuracy of visual observations of sexual 

 maturity of female Greenland halibut may be en- 

 hanced by histological analysis, for practical pur- 

 poses, field observations on the onset of first 

 maturity are adequate. Maturity of male Greenland 

 halibut was not included in the analysis here, since it 

 was extremely difficult to determine whether males 

 with growing gonads were maturing for the upcoming 

 spawning season or later. This uncertainty was prob- 

 ably a result of the timing of the surveys when milt 

 was not present in the testes and previously spawned 

 fish may have been fully recovered. 



The results of probit transformation analysis in- 

 dicated that the 50% maturity level (M 50 ) was 

 reached at a much smaller size for the Gulf of St. Law- 

 rence fish, whereas there was a trend of increasing 

 size at M 50 for fish from northern Labrador to the 

 southern Labrador-Northeast Newfoundland Shelf 

 area. Covariance analysis indicated that for the 

 Labrador-eastern Newfoundland areas the rate of in- 

 crease in the proportion of mature fish from one size 

 group to the next was the same. The Baffin Bank and 

 Gulf of St. Lawrence data differed from some areas 

 but not from others. More importantly, however, 

 were the significant differences in the intercepts of 

 the fitted lines for all areas. In biological terms this in- 

 dicates a significant difference in the sizes and ages 

 of M 50 for all areas. 



Molander (1925), in studying European plaice and 

 flounder in the Baltic, found that with increased 

 growth rate, maturity occurred at a lower age but at a 

 greater length. Bowering (1 976) found similar results 

 for witch flounder in the northwest Atlantic. Pitt 

 (1975) indicated for American plaice that faster 

 growing fish matured at an earlier age but all matured 

 at approximately the same size, suggesting that sex- 

 ual maturity is probably dependent on size, and in- 

 directly on growth rate, rather than on age. From 

 experimental research on sexual maturity of fishes, 

 Aim (1959) concluded that "with an initially good 

 growth rate maturity is reached at an earlier age than 

 an initially poor growth rate. The metabolic pro- 

 cesses are probably relatively fast with good growth 

 rate. Consequently, differentiation processes in 

 gonads and maturity apparently occur much earlier, 

 the opposite being the result of poor growth rate." 



The results reported here support in part the con- 

 clusions of Aim (1959). Greenland halibut from the 



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