306 



Abstract.— Daily growth increments 

 on otoliths were used to estimate the 

 age of larval and juvenile haddock, 

 Melanogrammus aeglefinus. and pol- 

 lock, Pollachius virens, collected on 

 Emerald and Sable Island Banks, east- 

 ern Canada, between March 1991 and 

 May 1993. The daily periodicity of the 

 increments was validated from obser- 

 vations of reared larvae. For both spe- 

 cies, the first increment was deposited 

 the day after hatching and thereafter 

 one increment was added daily. A Laird- 

 Gompertz growth curve was fitted to 

 length-age data for each species. 

 Growth rates in haddock and pollock 

 larvae varied significantly in different 

 years. For haddock, the lowest growth 

 rate was for the 1993 cohort, and 

 growth rates in 1991 and 1992 cohorts 

 were similar. For pollock, the 1993 co- 

 hort had the highest growth rate. The 

 average growth rate was 0.21 mm/d for 

 the first month and 0.42 mm/d for the 

 second month for larval haddock and 

 0.18 mm/d for the first month and 0.23 

 mm/d for the second month for larval 

 pollock. Growth continued exponen- 

 tially after the transition from a pri- 

 marily pelagic life to a predominantly 

 demersal one, which occurred at an age 

 of about 40-.50 d. No indication of a ces- 

 sation in growth was observed. Analy- 

 sis of length-age data indicated that 

 the accelerated growth of juveniles af- 

 ter 50 d in age could have reflected the 

 exploitation of a more abundant food 

 resource after settlement. Thus, pelagic 

 and early demersal growth appear to 

 represent distinct stanzas in the growth 

 history of these gadoids. 



Age validation and growth of larval and 

 juvenile haddock, Melanogrammus 

 aeglefmus, and pollock, Pollachius virens, 

 on the Scotian Shelf 



Casimiro Quiiionez-Velazquez 



Centre Interdisciplinano de Ciencias Marinas 



Playa El Conchalito s/n 



PO Box 592 



La Paz, BCS, Mexico 



E-mail address cquinone a vmredipn ipn mx 



Manuscript accepted 24 June 1998. 

 Fish. Bull. 97:306-319 ( 1999). 



A central problem in fisheries re- 

 search is understanding mechanisms 

 determining year-class strength. 

 Growth, which is considered critical 

 to the survival and subsequent re- 

 cruitment of larval marine fishes 

 (Houde, 1987), is likely strongly af- 

 fected by temperature and food 

 availability (Ricker, 1979). Food 

 limitation can affect survival di- 

 rectly by causing starvation (Lasker, 

 1975) or indirectly by retarding 

 growth rate which in turn increases 

 mortality from predators (Roths- 

 child and Rooth, 1982). In addition, 

 feeding conditions may change 

 markedly owing to density indepen- 

 dent factors, such as temperature, 

 which can directly affect growth 

 rates (Laurence, 1978). 



Ware ( 1975 ) suggested that growth 

 and mortality rates interact to deter- 

 mine survival offish populations, A 

 prediction of this hypothesis is that 

 predation is a major factor affect- 

 ing year-class strength and that 

 mortality due to predation is in- 

 versely related to growth rate 

 (Ware, 1975; Shepherd and Gushing, 

 1980). This hypothesis assumes that 

 average growth is below the maxi- 

 mum and that feeding conditions 

 that maximize growth are associ- 

 ated with minimal mortality. 



Galculation of reliable rates of 

 growth and mortality of larval fish, 

 and determination of when loss due 

 to recruitment is greatest, requires 



accurate determinations of age. Ac- 

 curacy and precision of growth es- 

 timates for larval fishes have been 

 greatly enhanced by the discovery 

 of daily growth increments on 

 otoliths (Pannella, 1971; reviewed 

 by Gampana and Neilson, 1985). 

 Ageing by counting otolith growth 

 increments, along with measure- 

 ments of the width of the incre- 

 ments, provides a means of estimat- 

 ing the relation between length at 

 age. In this way, growth curves, and 

 even individual growth rates, have 

 been calculated for a variety of spe- 

 cies (Brothers et al,, 1976; Struh- 

 saker and Uchiyama, 1976;Taubert 

 and Goble, 1977; Radtke and Wai- 

 wood, 1980). 



Daily increments have been 

 shown to occur in most species, nev- 

 ertheless validation of the fre- 

 quency of increment deposition is 

 required before larval age can be 

 estimated from otolith measure- 

 ments. To validate increment depo- 

 sition, Geffen (1987) recommended 

 sampling reared larvae throughout 

 the larval stage. This approach had 

 previously been used for a number 

 of species, for example, to determine 

 when the first increment is depos- 

 ited in Atlantic cod (Gadus morhua) 

 larvae ( Radtke and Waiwood, 1980) 

 and to validate the daily increment 

 formation in Pacific herring (CY (/pea 

 pallasi) (Moksness and Wespestad, 

 1989). In the present study, I vali- 



