54 DEPARTMENT OF THE NAVAL SERVICE 
7 GEORGE V, A. 1917 
were not utterly transformed so as to pass beyond favourable limits. If the northern 
coast has been sinking, it is possible that this has perm’ tted cold arctic currents to enter 
some of the bays, or to influence the adjacent water that enters on the tides, so that the 
temperature necessary for summer propagation (68° F.) is not attained. The extensive 
shallow flats of Richmond bay and other noted oyster-producing bays of the gulf of 
St. Lawrence offer the conditions favourable to the warming of the water to the point 
needed for propagation. 
As regards salinity, we know that oysters flourish best when situated where there 
is a tidal increase and decrease in the salinity of the water; but oysters do grow in 
waters of very different degrees of saltness; and also in places where there is remark- 
able uniformity in density. While too much emphasis has been laid on this factor, yet 
it remains highly desirable that further study be made of the relation of salinity to 
oyster feeding; but temperature, oxygen, and currents are of much greater significance 
in oyster growth and propagation. 
A study of the temperature of the waters where oysters are now extinct would dis- 
cover the cause of their extinction. From the tables of temperature! determined by 
Professor Copeland for Passamaquoddy bay, it is evident that oysters can not propa- 
gate in those waters; but there is less evidence that oysters flourished there in early 
times than for some of the bays of Maine. Even in Prince Edward Island there are 
fossil oyster beds in the vicinity of living beds; thus we conclude that there must be 
also other causes for the extinction of oyster life. 
In respect to frost, it is remarkable to what extent oysters survive exposure to 
freezing, when partially imbedded in mud and thawed out gradually. It is asserted 
that where the water is so shallow that the ice rests on the bottom, at low tide, the 
oysters are killed by the pressure, unless they lie on a soft bottom, where, however, 
they are in danger of being buried. On the other hand, a heavy fall of snow before ice 
forms, clogs up shallow waters and kills oysters and even clams, according to the testi- 
mony of intelligent and experienced oyster planters. The effect of melting ice, and 
especially snow, upon animal life has yet to be studied in a scientific manner. 
We are confronted with two opposing influences. Shallow waters, especially 
when so free from grass as to be swept by currents, favour oyster propagation in the 
summer, but are most unfavourable to oyster life in winter. Just here is a situation 
that can be advantageously handled by the art of man, so as to greatly improve upon 
nature; for the young oysters produced on the flats can be moved to deeper water 
on the approach of winter. This is never done under the conditions of a free or 
public fishery. It is in the interest of conservation that oyster farming be introduced 
to supplement natural production. The foremost difficulty encountered in this con- 
nection is not our inexperience and our ignorance of the proper way to raise oysters, 
so much as the opposition of those who believe in harvesting what nature produces 
without contributing the labour of cultivation. It takes many years of education 
and the observation of the increased harvest resulting from oyster farming, as well 
as the annually decreasing product secured by free fishing, to teach the oyster 
fishermen that it is to their interest as well as that of the general public, to promote 
scientific oyster culture. 
Man has been the oyster’s greatest enemy; although, if he will use remedial 
measures, he can more than counteract the destruction. It is supposed that the 
disappearance in recent historic times of some of the natural oyster beds is due in 
large degree to the increased amount of sediment carried into bays by rivers, on 
which saw-mills have been erected, or whose drainage areas have been cleared and 
ploughed. Sawdust and sand are the most injurious of the forms of silt; light mud 
is more readily handled by the ciliary feeding apparatus of the oyster; yet when silt 
is present as a nearly continuous suspension in the tidal currents, it seriously 
1 Contributions to Canadian Biology 1906-10, p. 286, ete. 
