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Fishery Bulletin 97(2), 1999 



12 



o 

 O 



12 

 10  



8  



6 



4 



2  



- 



PoUachius virens 



2 4 6 8 10 



Age (days after hatching) 



12 



Figure 3 



Number of increments enumerated on the sagittae of 

 haddock and pollock larvae as a function of known 

 age (days after hatching). Numbers represent the 

 number of larvae. The number of increments (NI) cor- 

 responds to the chronological age in d (AGE) of the 

 lar%'ae. Haddock NI = 0.99 AGE. n = 148. r- = 0.96. 

 and pollock NI = 1.09 AG£, n = 9, /-' = 0.82. 



the Aq |Specific growth rate at ^=0) did not vary sig- 

 nificantly (ANCOVA, P>0.05). The 1992 cohort had 

 the higher growth rates during the first 50 d follow- 

 ing hatching. Growth was linear at 0.18 mm/d fol- 

 lowing the predicted hatching size (1992 cohort), 0.13 

 mm/d (1993 cohort) through the first month, and 0.23 

 (1992 cohort) and 0.24 mm/d (1993 cohort) through 

 the second month. 



Discussion and conclusions 



Validation of increment deposition 



The present study shows that growth increments in 

 haddock otoliths are formed daily and suggests that 

 this is also the case in pollock. In both species, the 

 first of the regular increments is formed on the day 

 after hatching, and thereafter an additional incre- 

 ment is added each day up to 1 1 d for haddock and 4 



d for pollock. Otoliths develop before hatching, and 

 in haddock, 1 to 3 irregular increments are depos- 

 ited prior to hatching. These types of irregular in- 

 crements were not observed on larval otoliths of pol- 

 lock. A few embryonic growth increments of a lamel- 

 lar structure (such as I observed in haddock), have 

 also been reported in other species (Brothers et al. , 

 1976; Radtke and Dean, 1982; Watanabe et al. .1982; 

 Nishimura andYamada, 1984;Palomeraet al., 1988). 

 The spacing of embryonic increments is irregular, in 

 contrast to regularly spaced posthatching incre- 

 ments, which indicates that they might not be de- 

 posited at daily intervals. Whereas Radtke and 

 Waiwood (1980) did not observe increments formed 

 prior to hatching in cod (G. morhua), they did ob- 

 serve regular increments that were formed daily 

 starting one day after hatching. Brothers and 

 McFarland ( 1981 ) noted three diffuse increments in 

 the otolith core of French grunt (Haemulon flavo- 

 lineatiim ) and speculated that they were deposited 

 during the embryonic stage. Bolz and Lough (1983) 

 found 1-2 poorly defined increments enclosed by the 

 nuclear check in haddock larvae. According to the 

 above observations, it seems reasonable to infer that 

 the 1-3 irregular increments inside the hatch check 

 of haddock otoliths are formed sometime during the 

 2-3 week egg stage (Laurence and Rogers, 1976; 

 Fridgeirsson, 1978). 



Growth of haddock and pollock otoliths 



The sagittal otoliths of haddock and pollock larvae 

 are circular in shape at the age of 35-40 d. Subse- 

 quent sagittal growth is greater along the antero- 

 posterior plane, so that the otoliths become oval 

 shaped in older larvae. Radtke ( 1989) reported that 

 cod (G. morhua ) sagittae change as they grow, from 

 spherical to elongated to crenulated over a 65-d pe- 

 riod. In haddock and pollock larvae, circular-shaped 

 sagittae were observed until 8 mm SL, correspond- 

 ing to an age of 35-40 d. Then, the sagittal shape 

 begins to elongate as the result of growth of periph- 

 eral primordia, which corresponds to 30 mm SL (75- 

 80 d) in haddock and 23 mm SL (80 d) in pollock. 

 Thereafter the sagittae are not easily broken, and 

 their shape is distinguishable from that of other ga- 

 doid species. The last changes in otolith shape corre- 

 spond to the age when juveniles undergo metamor- 

 phosis to begin demersal life. Koeller et al. (1986) 

 inferred, from a series of midwater and botton trawl 

 surveys conducted in 1983 off southwestern Nova 

 Scotia, that the transition to the demersal habitat 

 by haddock occurs from June to August. 



In most otoliths examined, I observed a well-de- 

 fined, dark and discontinuous zone or ring laid down 



