326 



A. G. Huntsman 



represent merely the beginning of heavy interchange at the mouth of the large mass 

 of fresh water. 



In Head Harbour Passage, particularly the outer part, heavy tidal action and 

 irregular bottom keep the water quite thoroughly stirred, so that the plankton present 

 can easily be obtained in tows at any depth. Tows were made at two Stations (H.F. 50 

 and 35) in the outer part of the Passage on September 18 (at 50 only), 23, 26, 29 and 

 October 3. The quantities (cu.cm. after settling) of plankton (chiefly Calanus) were : 

 12; 8 and 16; 18 and 12; 180 and 95; and 80 and 27 respectively. There was thus a 

 very marked increase in quantity between 8 and 1 1 days after the rainfall. It would 

 seem to be possibly significant that, following the heavy indraft of Calanus into the 

 Passage, as found on September 29, there was a low amount outside on October 2, 

 but not on October 3. The movement outward of the mixed water from the freshet 

 might be expected to have such temporary effect in carrying outward much of the 

 plankton. 



10 



15 



DAYS 



20 



Fig. 3. Height above low water of surface of Digdeguash River at the Stillwater bridge in August, 



1951. 



The very definite result was that a dearth of Calanus in Head Harbour Passage was 

 changed to abundance when the water from the freshet worked its way out. Calanus 

 had been abundant in deep water outside, but the freshet made it abundantly available 

 to birds and to herring and other near-surface fishes by bringing it into the Passage, 

 where vertical currents lift it rather steadily toward the surface, overcoming its tendency 

 to descend from daylight. As far as the facts went, this was coincident with entrance 

 of quite salt water into the Passage, presumably from the depths outside where Calanus 

 was known to be abundant. 



RAINFALL AND SHIFTING OF PLANKTON 



On August 8 and 9, 1951, heavy rain (4-66 to 1-39 in.) fell over the drainage basin 

 of the Digdeguash River. The course of the discharge from the River into the head 

 of Passamaquoddy Bay was measured with a gauge at the first bridge above the point 

 where the River falls into the tidal Digdeguash Basin (Fig. 3). The heaviest discharge 

 was on August 10. 



The progress of the outflow of fresher water was determined, beginning at different 

 points on August 12, 13 and 14, by getting the salinities of surface samples taken 



