FISHERY BULLETIN: VOL 76, NO. 1 



Figure 6. — Distribution of Scomber scom- 

 brus eggs and selected surface isotherms 

 (°C) during June 1966. 



ATLANTIC MACKEREL 

 EGGS/STATION 



CRUISE D-66-7 

 JUNE 17-29, 1966 



no° a 



\ 



X 



\ 



\^ 



w 



«e" 



above the thermocline as reported by Sette ( 1943). 

 During Sette's study the thermocline occurred be- 

 tween 17 and 19 m. During this survey, at stations 

 where S. scombrus eggs or larvae were caught, the 

 thermocline was situated so that the surface 

 mixed layer was sampled by net 1 and was rarely 

 deep enough for the surface layer to be sampled by 

 net 2. 



I tested the two hypotheses that the mean 

 lengths (SL) were equal in catches from net 1 and 

 net 2 during both day and night tows, and found in 

 both cases that the mean lengths were not sig- 



nificantly different between the paired catches. In 

 another analysis I tested for differences in mean 

 lengths between day and night tows. In this case 

 the pairs tested were adjacent stations either on 

 the same or adjacent transects. The result of the 

 test was not significant, i.e., there was no sig- 

 nificant difference between the means. I used 

 analysis of variance in these tests for differences 

 in mean lengths between the two nets and be- 

 tween light regimes because this procedure segre- 

 gates the known differences in lengths observed 

 over the geographical distribution. 



106 



