Quinonez-Velazquez: Age validation and growth of Melanogrammus aeglefinus and Pollachius virens 



307 



dated whether increments are deposited daily in 

 haddock otoUths (Melanogrammus aeglefinus ) using 

 the same approach. PreHminary results on larval pol- 

 lock (Pollack ius virens ) are also presented. Finally, daily 

 increment analyses are used to estimate age and growth 

 rates of larval and juvenile haddock (M. aeglefinus) and 

 pollock (P. virens) from the Emerald and Sable Island 

 Banks on the Scotian Shelf off eastern Canada. 



Materials and methods 



Study area and collection of larvae 



The Scotian Shelf is a 62,000 km^ area with an aver- 

 age depth of 90 m. It is bounded on the southwest by 

 Northeast Channel entering the Gulf of Maine and 

 on the northeast by the Laurentian Channel and Gulf 

 of St. Lawrence. Several shallow offshore banks along 

 the outer edge of the shelf are separated from one 

 another by deeper channels that open onto interior 

 basins having depths of >100 m (O'Boyle et al., 1984). 

 The general water circulation on the Scotian Shelf is 

 dominated by the Scotian current which flows south- 

 westerly and parallel to the Nova Scotia coast and 

 which carries a mixture of slope water and diluted 

 waters from the Gulf of St. Lawrence (e.g. Sutcliffe 

 et al.. 1976; Drinkwater et al., 1979). 



Eggs, larvae, and juveniles of M. aeglefinus and P. 

 virens were collected during 20 surveys made on 

 Emerald and Sable Island Banks (Fig. 1) from March 

 1991 to May 1993 (Table 1), as part of the program 

 of Ocean Production Enhancement Network (OPEN) 

 (Griffin and Anderson, 1993). Sampling was con- 

 ducted using a grid of 45 stations (Fig. 1) with an 

 interstation spacing of approximately 30 km. A 50- 

 cm bongo frame with 150- and 250-|.im mesh nets 

 (March-May 1991 ) as well as a rectangular midwater 

 trawl (RMT, 2-8 m^) (Baker et al., 1973) with nets of 

 2 m^ (333-|.im mesh) and 8 m- (1600-|.tm mesh) were 

 used. At each station, duplicate oblique hauls were 

 made from near the bottom to the surface at 2.0-2.5 

 knots, with a retrieval time of 30 min. After the stan- 

 dard grid stations were sampled, the area of maxi- 

 mum abundance of larval fish was revisited so that 

 48 h of vertical sampling could be conducted with a 

 BIGNESS sampler (1 m-) (Eastern Marine Services 

 E-Z-Net, Dartmouth, NS) fitted with ten 333-nm 

 mesh nets (June 1991 to May 1993). Ten discrete 

 depths were sampled every 4 h. Deployment sam- 

 pling depths were spaced at 5-m intervals, from the 

 bottom to the surface, and fished for 5 min at 2.0- 

 2.5 knots. Most larval haddock and pollock were 

 - sorted at sea and preserved in 95% ethanol. Tempera- 

 ture and salinity profiles were recorded at each station 



Figure 1 



Study area showing stations where lar\'al and juvenile had- 

 dock and pollock were collected on the Scotian Shelf from 

 March 1991 to May 1993. Isobaths are in meters. 



with a Sea Bird CTD probe (Sea-Bird Electronics, Inc. 

 Bellevue, WA ) connected to the electronics unit of the 

 RMT or BIGNESS sampler, or both. When the RMT or 

 BIGNESS, or both, were not used, independent CTD 

 casts were made at each station. 



A subset of pollock and haddock larvae were vid- 

 eotaped at sea by using a stereo dissecting micro- 

 scope connected to a video camera and a magneto- 

 scope and were then individually preserved in 95% 

 ethanol. One to two months later, each fish was mea- 

 sured in the laboratory to the nearest 0.1 mm with a 

 stereo dissecting microscope with an ocular microme- 

 ter. The unpreserved standard lengths were mea- 

 sured from video images recorded at sea and pro- 

 jected on a television monitor linked to an image 

 analysis system. Linear regression of unpreserved 

 standard length (SL, obtained from the videotape) 

 to preserved standard length (PSL. after preserva- 

 tion in ethanol) for haddock (SL=1.531 -i- 1.005PSL, 

 /! = 129, r-=0.99) and pollock (SL=0.710 -i- 0.969PSL, 



