In the day hauls the large larvai^ vfcre not only less numerous than 

 in the night hauls, but also appuared to bo distributed in soraev/hat deeper 

 levels . A greatc-r relative number of larvae at the deeper levels in the 

 daytime than at night might r^jsult from more successful dodging of the net 

 in the t^etter illuminated upper layers of i;ater. A greater absolute number, 

 however, could result only from dovmward migrauion in the daytime, providing 

 the overall concentration •v/ere not greater. Such a dov/n;;ard migration 

 might virell occur as a result of negative phototropism. Comparison of the 

 night and day hauls for stations 2Up2 and ZW^h (fig. h) reveals that there 

 actually were more larvae at the deeper levels in the day hauls. Four lar- 

 vae were taken in the day series at S? meters, and one at 73 meters, Virhilc 

 none virere taken at either of these levels in the night series. The signi- 

 ficance of these differences vias tested by means of Bayes' theorem, (using 

 the formulation of Pearson, 1930, page Ixx) considering a success, the pres- 

 ence of a larva at the indicated depth, ahd assuming the sfuae overall con- 

 centration for day and night (in other v/ords assuraing that the lesser num- 

 bers in the upper layers in the daytime were due to dodging of the net). 

 The computation gave values of P of .06 at S? meters and .$0 at 73 meters. 

 The latter, of course, does not indicate a significant difference betiTeen 

 day and night hauls, but the former, closely approaching the conventional 

 significance level of .05, gives some indication of an actually deeper dis- 

 tribution in the daytime. 



In applying this result to the prediction of vertical distribution, 

 a knov.'lodge of the penetration of light at various tines of day is neces- 

 sary. Unfortunately, no empirical data for the area of our survey are 

 available, and we are forced to argue by analogy with data collected else- 

 v;here. G. L. Clarke (193U) has sho^m in his graphs that submarine irradi- 

 ation in the Atlantic Ocean reaches nearly its maximum value shortly after 

 sunrise, and is maintained there until shortly before sunset-. Accordingly, 

 extension of the regular hauls below 73 meters between sunrise and sunset 

 would seem to bo necessary in order to make svir^ of sampling all strata in 

 which larvae were' to be found. 



SmMiklU Aid CONCLUSIONS 



Analysis of catches of pilchard eggs nnd larvae taken in serial- hauls 

 in 1939 and I9UI indicates the following relationships and effects: 



1. A positive correlation of c one enti-at ions of eggs and larvae 

 With temperature, at least \.-ithin the range of 10° to 17° C. 



2. An apparent dodging of the nets by the larger larvae, in the 

 layers of ii/ater ^vhich are illuminated in the daytime. 



3. A negative phototropism for the larger larvae^ 



Such relationships with physical conditions as have been indicated 

 by the present study may, of course, hold true only for the particular set 

 of occanographic conditions prevailing at the times and places where the 

 data were gathered. For instance, the relationship between the horizont-al 

 distribution of pilchard eggs and temperature as indicated by our regular 

 spavming surveys for 19U1 was quite different from that found in 19U0. 



N 188 



