160 



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u. zoo J 



U N K N 



1- 







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i 



U N K N W "N 



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T 



T 



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Feb- Morch April 



Moy 



July 



Aug Sept 



Figure 20.--Depth distribution of herring schools in Passamaquoddy Bay as determined by sonic-sounder recordings (upper) 



day, (lower) night. 



and results of echo-sounder surveys sug- 

 gest that fishing mortality is low, hence 

 there should be no reduction in the abun- 

 dance of herring inside the Bay. 



Herring will be unable to enter Cobs- 

 cook Bay directly from the outside except 

 in insignificant numbers through the nav- 

 igation locks and filling gates. Entry 

 into Cobscook Bay and exit from Pas- 

 samaquoddy Bay will be possible only 

 through the turbines. As a result, move- 

 ment into Cobscook Bay and away from 

 both Bays will be altered both in time 

 and direction. Most of the water entering 

 the Western filling gates will have been 

 discharged from the low pool, whereas 

 inflow through the Letite filling gates 

 will be mostly "new" water from outside 



the dams. Therefore, recruitment of 

 herring to Passamaquoddy Bay is ex- 

 pected to be mainly through the Letite 

 filling gates. 



The predicted salinities of 20 to 30 

 parts per thousand in the upper (10 to 15 

 feet) water layers of the high pool during 

 normal summer conditions are well within 

 limits that herring can tolerate. If tem- 

 peratures in this layer reach or exceed 

 the predicted value of 68° F. and especi- 

 ally if they rise above 70° F., herring 

 mortality might be high. Temperatures 

 of this order may occur only in isolated 

 or sheltered coves, and any mortality due 

 to high temperature and low salinity 

 should be limited in time and extent. It 

 is possible that herring will avoid 



28 



