Orig. Ms. 500
PASSAMAQUODDY DAMS AND THE FISHERIES
A.G. Huntsman
The fisheries of the region, more particularly that for the herring,
which is the principal one, reach their maximum value in the vicinity of
Campobello island, and possibly extending to Grand Manan.
There is a rapid
drop in volume going east to Saint John and north to st. Stephen, and a slow
drop going west to Portland and south to the western end of Nova Scotia.
The
chief fishery is for young herring, which are taken by weirs operating within
two hundred feet of the beach.
The summer distribution of the coldest surface
water of the region shows a close parallelism to that of the best weir
fishery, or, to express it differently, the distribution of the weir fishery
corresponds with that of the coldest surface water along the ·coa s t , the weir
fishery being less and less successful as it is extended to regions with
warmer surface water.
This cold water is the result of local factors, not of an arctic
current.
The local influences, which actually keep the surface water so cold,
are two in number and these are closely connected in their action.
The more
obvious one is the churning that the strong tidal currents cause in the
channels and over the shoals, which mixes the warm surface water with the
deep colder water.
Associated with this is upwelling, which particularly
results from a deep current striking a bank.
Upwelling is shown at the
entrance to Passamaquoddy bay by the surface water at that point as compared
with other places in the region having (1) the lowest temperature, (2) the
highest content of phosphates, and (3) quantities of deep-water animals, on
which large numbers of sea birds feed.
The upwelling brings the cold water
from below to be mixed with the warm water of the surface and so to lower the
temperature of the latter.
It also brings to the surface the fertilizing
salts required for the continuous growth of the floating and attached
vegetation of the upper well lighted waters.
While churning and upwelling to a greater or less degree occur at
many places in the region and in fact quite generally along the coast from
Saint John to Portland, the most important ten-mile stretch for these processes
on the whole coast is to be found at the entrance to Passamaquoddy bay.
It
is here that the churning is most active and that the greatest amount of
water is involved.
It is practically certain that the mouth of Passamaquoddy
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2.
bay sees much more upwelling and from deeper water than any other restricted
part of the coast line of the Gulf of Maine and the Bay of Fundy.
These
processes are so pronounced at this place because of the peculiar bottom
configuration and the great volume of the moving water.
The installation of the dams will reduce the flow of water to a
low value of from one-fifth to one-quarter the present amount.
It is
inevitable that the amount of churning and upwelling will be greatly reduced
even if not precisely in the above proportions.
As a result the cooling
effect will be greatly lessened and the surface water will warm to a higher
temperature 'unde r the summer sun than is now the case.
The general dominant
drift of the water is from northeast to southwest along this coast.
Therefore,
any stoppage in the present chilling effect of this Passamaquoddy bay
churning and upwelling will result in a rise in temperature of the surface
water next the coast that will extend to the southwest, so that the warming
effect will be felt generally in the region of important weir fishing.
The success of these weirs depends upon there being a marked con­
centration of young herring close to the changing tide line.
The herring,
both old and young, have a narrow temperature range, and what is known of
its natural history suggests that the present summer temperature of the
waters of the coast from Passamaquoddy bay to Mount Desert is about the upper
limit for this fish.
There is every reason to believe that, if this region
were much warmer than it now is, the young herring would move out into some­
what deeper water during the summer months as they now do both to the south
and to the north.
Anything that will permit the surface waters to warm to
a greater extent than they now do will damage the weir fishery.
Although the
data are not sufficient to establish quantitatively the relative importance
of the Passamaquoddy mixing in the general mixing mechanism along the coast,
yet it is certainly much the most important part.
Its stoppage becomes very
important when the strong evidence that the present temperature is near the
critical point for the herring makes even a slight warming a dangerous thing.
A stoppage in the bringing up of deep water with its load of
nutrient salts will correspondingly impoverish the marine vegetation of the
neighbouring regions and thus render the latter less fertile as pastures
for fishes.
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3.
Inside Passamaquoddy and Cobscook bays the weir fishery for herring
will be entirely ruined because the surface water will become so brackish
and warm in summer that such herring as may enter these bays will be forced
to remain in the deep water.
There is a very good precedent for estimating
the extent to which the surface water will warm from what actually happens
in the Kennebecasis bay above Saint John.
In place of a full tidal surge
in and out of that bay as in Passamaquoddy, the water falls in and falls out,
as would be the case in the latter with the .dams installed.
As a result the
surface water is warm and of very low salinity and the sea fish are limited to
the deep water.
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