AGE OF YOUNG HADDOCK 



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AG E 



Figure 5. — Catch por day of haddock taken in Georges 

 Bank Fishery. 



methods agreed in 6*2 percent of the cases, but 

 closer agreement (73 percent) was obtained when 

 only fish 2 through 5 years old were examined. 

 M. Graham (1929) has stated that scale-otolith 

 comparisons do not prove the validity of either 

 method unless it is demonstrated that the periodic 

 zones are formed simultaneously on both the scales 

 and otoliths. Such comparisons may serve as 

 indices to the validity of one method if it is sup- 

 ported by tlie other method. 



Confirmation from Tagging 



Tlie I'ecapture of marked fish of known age is 

 the most direct means to validate age determina- 

 tions, since the time parameter is precisely known. 

 The technique is essentially this: the fish are 

 marked and, before they are released, scales are 

 removed for age determination. When a marked 

 fish is recaptured, a second age determination is 

 made and compared with the first. Since the 

 time at liberty is known, ajiy growth can be 

 directly compared to time. 



To examine this growth, scales were taken at 

 the time of recapture from 32 tagged haddock and 

 compared with scales taken from the same fish at 

 the time of tagging. The fisli were at liberty 

 from 9 to 150 weeks. The scales were examined 

 as follows : "at return" and "at tagging." Scales 

 from each fish were impressed on plastic slides (64 

 in all). Each slide was identified only by a code 

 number and the month in which the scale 

 sample was taken. All of the slides were exam- 

 ined independently by two experienced scale read- 

 ers, who marked the annuli for each scale on a 

 card. Wlien the readings were completed, the 

 markings on the cards were compared to determine 

 whether both readers had interjireted the same 

 zones as annuli. Both sets of scales were identi- 

 cally interpreted for 29 of the 32 fish (table 5) ; 

 the 3 questionable sets M-ere re-examined by both 

 readers together. Two of the fish in question had 

 not formed identifiable annuJi for one of their 

 years at liberty ; one was at liberty for 105 weeks 

 and the other for 150 weeks. On the scale of the 

 third fish, a zone was identified as an annulus by 

 one of the readers but not bj' the other. This zone 

 was formed immediately following tagging and 

 perliaps lesulted from interruption of growth 

 caused by capture and tagging. It is significant 



