286 



Fishery Bulletin 91(2). 1993 



2 - 5 mm 6  8 mm 9 - 13 mm 



75 50 25 25 50 75 150 lOO 50 50 100 1 50 4 30 20 iQ 10 ffl 



J 30 



£40 



143/IOm 2 250/IOm 2 473/IOm 2 483/IOm 2 



9/HW 66/IOm 2 



2  5 mm 6 8 mm 9 13 mm 



.,6420246 30 20 IP 10 20 30 3 2 I 12 3 



7/IOm 2 16/IOm 2 35/IOm 2 58/IOm* 



SAUNITt(psu) 

 3200 2 4 6 8 3300 2 



/10m 2 7/IOm 2 



TEMPERATURES) 



20- 



l 30 ' 



^ 40 - TEMPI 



Q. ] 



° 50- 

 60- 



Figure 7 



Mean day and night vertical distribution tx 'i/lOOm'l of (A) 

 haddock Melanogrammus aeglefinus and (B) cod Gadus 

 morhua size-classes of larvae collected by the 1 nr MOCNESS 

 on well-mixed Site 81-11 following the storm on 24-26 May 

 1981. Estimated water column abundances (»i/10m 2 ) are in- 

 cluded at bottom of plots. Temperature and salinity profiles 

 are plotted as depth stratum means (•) and 95% confidence 

 limits ( 1. 



water column than smaller larvae. However, when the 

 water column was well-stratified on 21 May and 

 weakly-stratified on 28 May, in both day and night all 

 sizes of larvae were located in or above the thermo- 

 cline. The single day and night tows were not suffi- 

 cient to base firm conclusions on diel differences. 



In mid-May 1983, two sites were sampled in weakly- 

 stratified waters across the southern margin of Georges 

 Bank. At Site 83-1 (Fig. 10), mean day and night verti- 

 cal distributions show haddock and cod larvae distrib- 

 uted broadly through the water column on 13-14 May, 

 but each of the three size-classes had a different depth 



B Cod 



SALINITY (psu) 

 3200 2 4 6 8 3300 2 



TEMPERATURECC) 

 5 10 



KH 



10 

 20 



J 30 ' 



t° 

 = 50 



60 



70 



80- 



a 2-5mm I6/I0m 2 



6 6-Smn 2 0/I0m 2 



c 9-l3mm 04/IOm 2 



Figure 8 



Day vertical distribution (.? 'i/lOOm') of 

 size-classes of (A) haddock Melano- 

 grammus aeglefinus and (B) cod Gadus 

 morhus larvae collected by a single 1 nr 

 MOCNESS tow on weakly-stratified Site 

 81-11 following the storm on 28 May 1981. 

 Estimated water column abundances (n/ 

 10m-'l are included at bottom of plots. 

 Temperature and salinity profiles are 

 plotted as depth stratum means (•) and 

 95% confidence limits I ). 



distribution. Recently-hatched larvae (2-5 mm) were 

 most abundant at 10-30 m both day and night. The 6- 

 8 mm size-classes of both species were more broadly 

 distributed and most abundant at 10-50 m depths, with 

 haddock tending to be deeper in the water column by 

 day than cod. The 9-13 mm size-class for both had- 

 dock and cod had a pronounced diel shift in day-night 

 distribution patterns: most larvae were in the lower 

 half of the water column by day but in the upper half 

 at night. The maximum density for both species was 

 at 10-20 m. There were significant (p<0.05) interac- 

 tions for each combination of depth, time, and size 

 (ANOVA; Table 2C). 



A time-series of larval catches in relation to the ther- 

 mocline region at Site 83-1 is shown in Fig. 11. Al- 

 though the mean depth of the thermocline centered at 

 -20 m, its bounds varied between 10 and 40 m, per- 

 haps due to the tides. While the population centers of 

 cod and haddock larvae tended to be associated with 



