446 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Table 4. — Age composition of .'il9 Georges Bank haddock, 

 hy 3-cm. groups 



consist of an irregular line with its highest point 

 near the ordinate and sloping downward to the 

 right. But haddock spawn in one relatively brief 

 time of the year; the young from a single year's 

 spawning are about the same size and fonn a mode 

 in a length-frequency graph. The small fish are 

 the young fish; i.e., fish represented by the fii-st 

 mode have no annulus or only one annulus on their 

 scales. Fish represented by the second or third 

 modes have two or three annuli, respectively, on 

 their scales. 



AGE DISTRIBUTION 

 LENGTH DISTRIBUTION 



LENGTH IN CENTIMETERS 



Figure 4.— Age analysis of the length composition of 419 

 Georges Bank haddock collected on Albatross III 

 cruise 56, February 1955. 



Confirmation from Age Distributions 



Long-term observations of a fish population 

 when the age frequencies are plotted will show the 

 progression of strong year classes through the 

 fishery, but this test only demonstrates that the 

 majority of age readings are correct and is not 

 meaningful unless the stock is adequately sampled 

 (M. Graham, 1929). The year-class progression 

 becomes less valuable when the outstanding year 

 classes cease to be dominant and when the scales 

 of the older fish become difficult to read. 



In general, dominant year classes remain domi- 

 nant in an age-frequency histogram for the first 

 few years. Unfortunately, the stronger year 

 classes appear to lose their dominance (in age fre- 

 quency) in later years. This is due, no doubt, both 

 to errors in scale reading and to differing mortality 

 rates. 



Year-class progression is demonstrated in the 

 graph of the catch per day, by age, of Georges 

 Bank haddock landed at Boston from 1948 through 

 1957 (fig. 5) and represents scale readings from 

 •12,000 haddock. The relative strengths of several 

 year classes are also shown. For example, the 

 1948 year class of haddock was very large and is 

 well represented by the catch of 2-year-old fish in 

 1950. The 1948 year class also dominated the 

 landings as 3-year-olds in 1951 and were well 

 represented as 4-year-olds in 1952. However, in 

 1952, the 1948 brood is about equal in strength 

 to the less successful 1949 brood, and by 1953 it is 

 subordinate to the 1949 brood. 



Similarly, the 1950 year class formed a large 

 part of the catch as 2-year-olds in 1952 and as 3- 

 year-olds in 1953. The 1951 year class was rela- 

 tively poor, but the 1952 year class appeared in 

 large numbers in the landings as 2-year-olds in 

 1954 and as 3-year-olds in 1955. 



These observations tend to support the validity 

 of our age readings. It will be noticed, however, 

 that these strong year classes appear to lose their 

 dominance after about the fourth year. Wliether 

 this is due to differential mortality or to age 

 reading error, or both, remains to be resolved. 



Comparison of Scales and Otoliths 



A detailed study of haddock scale-otolith com- 

 parisons was reported by Kohler and Clark (1958) 

 who examined material from 764 Georges Bank 

 and Nova Scotia fish 1 to 13 years old. The two 



