Effect of freshets on Passamaqiioddy plankton 325 



at 50 metres depth, which is deeper than the Bay in general, were for example on 

 October 12, 1933: 30-99 and 31-73 respectively. Also, the salinities at the same 

 depths on the same day at Station No. 5 outside Head Harbour Passage were: 31 ^X 

 and 32-32° , respectively. Ket( hum and Kkhn (1953) have calculated that in August 

 of 1951 the mixed water moving out of the Bay near its mouth was over 100 times as 

 great as that of the discharge from rivers, and that outside the Passages it had 

 increased to nearly 600 times. 



Owing to their shallowness, the Letite Passages do not permit much movement 

 of water through, so that the principal outlet for mixed water and the principal inlet 

 for salt water is Head Harbour Passage. Also, movement through the Letite Passages 

 is more inward than outward, as determined through a complete tidal cycle in 1951, 

 But, there is very definite passage out of mixed water through Letite and passage in 

 of salt water, as well as very heavy mixing of the two. 



RAINFALL AND PLANKTON INDRAFT 



Calanus is not produced to any particular extent in the Passamaquoddy region, 

 but is there as an immigrant from the Gulf of Maine (Wright, 1929; Fish, 1936). 

 It was very abundant at Prince Station No. 5 just outside Passamaquoddy Bay in the 

 late summer of 1933. Vertical hauls with the No. (bolting cloth measure) net from 

 90 to metres gave the following quantities in cubic centimetres of settled plankton 

 (chiefly Calanus) on the dates indicated: 13 on July 10; 9 on August II; 22 on 

 September 15. 



The quantity of Calanus at Station No. 5 varied greatly from September 23 to 

 October 3. Deep tows were made on the former date, giving large quantities at from 

 100 to 50 metres and at about 90 metres. On October 2, a vertical haul gave only 

 2 cu.cm. Yet, deep tows made the next day revealed even greater abundance than on 

 September 23. 



During the night of September 17-18 there was a very heavy rainfall o\er the 

 basin that drains into the head of Passamaquoddy Bay, over 5 in. falling at St. Andrews 

 and 4-81 in. at St. George on west and east sides of the Bay, and 3-25 in. at Mc.Adam 

 at the head of the drainage into the Digdeguash River. Three days later, another inch 

 of rain fell over the area. It is estimated that these rainfalls more than doubled the 

 amount of fresh water being discharged into the Bay. 



Ketchum and Keen (1953) have calculated that the mean flushing time for the 

 removal from Passamaquoddy Bay of freshwater discharged into it is I5-S days, 

 and they conclude that "it seems probable that a flushing time of about 15 days 

 should be approximately correct ". In late summer of 1933, there were three heavy 

 rainfalls recorded, on August 25, September 18 and October 7. Weekly determina- 

 tions of bottom salinity in the middle of Passamaquoddy Bay showed that higher 

 salinity returned between 5 and 13, 9 and 16, and II and IS days respectively, if 

 such return has a constant period, it will, therefore, lie between 1 1 and 13 days after 

 the rainfall. After the freshet of September 18, salinities were measured for Prince 

 Station No. 9, which is ofT Clam Cove Head at the mouth oi Passamaquoddy Bay 

 where it joins Head Harbour Passage, on September 23, 26 and 29, and on October 3. 

 The values at 50 metres depth were 31-78 , 31-67 , , 31-85 and 31-89 ;., 

 respectively. This shows that Salter water was entering the mouth of the Bay 1 1 days 

 after the rainfall. What relation this has to the flushing lime is not clear. It may 



