Effect of freshets on Passamaquoddy planklon 323 



zooplanktonts keep, and upon the depths of the two movements, as to whether these 

 will be carried oceanward out of the estuary or riverward to be concentrated at the 

 head of the estuary. The strengths and depths of the movements will depend, not only 

 upon the degree of tidal mixing, but also upon the amount of river water. Any 

 estuarial concentration of zooplankton there may be, will be increased by freshets 

 in the river. 



HOURS OF DAY 



Fig. 2. Vertical distribution of Calanus throughout the 24-hr. day at Prince station No. .'> in the Bay 

 of Fundy, as inferred from vertical tows made on September 20, 1926, through ten metres of water 

 at different depths on three occasions: (1) between 2.50 and 3.55 hr., (2) between 4.35 and 5.25 hr. 

 and (3) between 7.15 and 7.55 hr., as shown by vertical lines. Periods of sunlight and moonlight arc 



shown at the top, and numbers of Calanus arc per tow. 



While the zooplanktonts may be at the proper depth during the day for transport 

 riverward, their migration towards the surface at night may well result in their being 

 carried oceanward. So complex is the situation that, as yet, only their actual distribu- 

 tion can be depended upon to show in which direction particular zooplanktonts have 

 moved. 



