MEMORANDUM FROM DOMINION COMMISSIONER OF FISHERIES
re UNFAVOURABLE CONDITIONS FOR COD IN THE WATERS OF LAKE MELVILLE.
June 23rd, 1924.
The results which were obtained in regard to temperatures and salinities in Labrador waters, included in the work of officers of the Hydrographic Survey, during July, August and September, 1921, are sufficient to satisfy an expert Marine Biologist that the conditions existing in Lake Melville are so unfavourable for cod that neither their spawning, nor their life-development, nor their adult life would be possible in the waters referred to.
Biologists have determined that the presence of cod requires abundance of food, appropriate temperatures and favourable conditions for schooling and for breeding purposes, dependent especially upon salinity and consequently specific gravity. Specific gravity of sea water in certain areas, such as those under consideration, is such as to prevent cod eggs from floating and to enable them to develop normally. In the records attached, the decision, as to the bearing of existing conditions on the presence or absence of cod fish, is complicated by the fact that the specific gravity of sea water varies with the amount of salts dissolved, and this depends upon temperature. With a rise in temperature, sea water expands and becomes lighter, but the reverse takes place when cold conditions prevail and the water increases in weight down to the freezing point, but the freezing point also varies with the salinity. If, therefore, a series of specific gravity observations are recorded at the same temperature, it is evident that any difference found in this specific gravity is due to salinity alone.
The cod is not a surface fish, but spends most of its life near the bottom at depths from 15 to 50, or 100 fathoms. It is important to notice that the salinities recorded at these depths in the attached salinity determinations are all far below the 35 parts of dissolved salts, which occur in solution in normal sea water, at freezing point.
It must be remembered that in such inlets, lakes, or lagoons, as Lake Melville, there is a restricted entrance or “ narrows ” admitting inflow or outflow from and to the ocean, and especially submarine ridges, which usually occur in such narrows, either as remains of a former barrier to the sea, or as accumulations of material of a glacial or aquatic origin, that is
deposited either by ice sheets in former times and, therefore, of the character of “ Moraines,” or as material deposited where the outflow meets the inflow of the tidal water, and the specific gravity is found to decline, and it may sink to so low a salinity as 20, which is that observed in the Baltic Sea and in the Black Sea. The addition of large quantities of fresh water poured down from rivers, ice sheets, or vast areas of deep snow, also tends in the same direction.
In the records attached, the salinities noted, as already pointed out, at depths of from 15 to 50 or 100 fathoms are chiefly interesting because they are practically prohibitive of the presence of large schools of cod and prevent, therefore, the development of fisheries on any commercial or extensive scale. The conditions limit the amount of food on the bottom, which is essential for cod fisheries. The famous Dr. Johan Hjort, one of the greatest fishery experts in the world, and formerly Director of Fisheries for Norway, states in his report on the Canadian Fisheries Expedition, organized in 1914–15 under the auspices of the Dominion Government, that “ the cod is a bottom-feeding fish, belonging essentially to the strata near the sea floor where its food is found and where its spawning takes place ” (Canadian Fisheries Expedition 1914-15, page 36).
Professor A. P. Coleman, who has published one of the recent scientific reports on Labrador, particularly referring to the geology of the coast, states that cod do not appear to go far into any of the fiords on the Labrador coast, and on his visit to Hamilton Inlet, he saw no cod being taken, and saw not even in fishing schooners, though the waters outside were swarming with fishing craft. In a private letter he agrees that “ cod are far less numerous in narrow brackish and shallow waters, is a correct view,” and he adds that he doubts if any cod go so far inland as the waters of Lake Melville.
There is uniformity amongst the leading experts upon sea fisheries that the cod is a typical salt water fish and is a bottom fish and that it occurs normally in salt water. Exceptionally it resorts to inshore shallows, but only spasmodically, when such fish as the “ capelin ” go inshore for spawning purposes in immense schools. Cod follow the capelin, but the period of spawning lasts a very short time, and the capelin do not enter brackish or fresh water. After the capelin run is over the cod return to their ordinary feeding grounds, where (as Professor Hind in his report published in 1877 on the fisheries of British North America, states) “ they are caught with long lines, or baited trawls actually at the bottom of the sea during December, January, February and March, but from July to September they are often found a few fathoms above the bottom.” The whole cod family (Gadidae), as Dr. Günther, Head of the Fisheries Section, British Museum, London, said in his “ Study of Fishes,” page 539, that only two or three species inhabit fresh waters, and the cod family includes nearly sixty different species.
Dr. Richard Parnell is even more emphatic in his well-known work on the “ Fishes of the Firth of Forth, Scotland,” and said nearly a century ago, that cod are never found but in salt water and remain habitually in the depths of the sea. They never ascend up the rivers or even generally frequent the
shores, excepting for the purpose of depositing their spawn, or attracted by migrating hordes of small fish, such as herring and launce. Dr. Theodore Gill, the eminent United States Authority on fish, as quoted by Dr. Starr Jordan (“ The Study of Fishes,” Vol. II, page 534), said “ the ocean banks of moderate depth are the favourite resort of the cod. . . .” It is found up the estuary of the St. Lawrence, though how far has not been definitely stated, probably not beyond the limits of brackish water.” Dr. Jordon himself adds “ that along the coasts of New England, the Middle States and British North America, and upon all the off-shore banks of these regions, cod are usually found in great abundance during part of the year at least. Some recent investigations in the Bay of Fundy show bow marked and definite is the limit of the distribution of cod, as influenced by salinity and temperature, and Dr. A. G. Huntsman, one of our best authorities on the Atlantic Fisheries, recently reported that his investigations in the Bay of Fundy show that cod have a very marked and definite limit in those waters, and that above this limit they practically do not occur.
Dr. Huntsman states in a recent paper on “ The Fishes of the Bay of Fundy ” (contributions to Canadian Biology, 1921, Nos. III to XII, page 20) “ Cod are abundant at Grand Manan, but decrease in abundance towards Passamaquoddy Bay ” and he further states on page 5 “ in the Bay of Fundy proper, viz., the main portion exclusive of the tributary, the fish fauna shows on the whole what would be expected from its long funnel shape.” Outer deep water with a depth of more than 50 fathoms ends at the mouth of the St. John River and the large catches of the important bottom feeding salt-water fishes, viz., the cod, herring, and hake, are restricted to the shoal water bordering this deep basin, the catches decreasing rather abruptly above this basin.” Such a sudden cessation of cod at definite limits where the water begins to change from normal sea water to brackish water has been noted in many localities.
Scientific observations have shown that cod eggs are buoyant and float lightly within a few fathoms of the surface, but they will float only in layers of water of the same specific gravity as their own. Experiments have shown that cod eggs, and newly hatched fry, find favourable conditions in strata whose specific gravity is 1.021 with a salinity of at least 30 to 35. When the specific gravity is reduced to 1.020, no less than 50% of the eggs and young have been found, by actual experiment, to sink to the bottom and with the specific gravity reduced to 1,019 nearly the whole of the eggs sink to the bottom. No great fishery like a cod fishery can exist if the conditions are unfavourable for the breeding and for the development of the eggs and fry, for upon this depends the abundance of adult fish essential to an important cod industry.
It is true that Dr. Hjort found cod eggs near the bottom in the Gulf of St. Lawrence at a temperature below freezing (i.e. 32° F.) but this low temperature was demonstrated to be most unfavourable, for it prolonged the development of the eggs to such an extent that the early cleavage stages and very early embryonic condition showed little development even so late
as July and August and the spawning season there apparently commences in April and May.
For favourable development and production of young cod in abundance, the period should not exceed from three to six weeks.
The observations in European waters have shown that cod spawn as early as March and April ; indeed those are the chief months, and all the spawning is over by May. This has been abundantly shown to be true of the cod in Norway. A temperature of 37° F. to 43° F. seems to be the most favourable, although cod will hatch out up to so high a temperature as 54° and 57° F. ; but there is always a loss of eggs and fry by too rapid development, and the same applies to a development which is too slow and prolonged. Proof of this is furnished by the high degree of mortality in cod eggs and young fry reported in Dr. Hjort’s investigations in the Gulf of St. Lawrence. The causes of this mortality are no doubt complex, but the low temperature and extremely prolonged development must have been a principal cause. Continuous and extreme cold, and still more, the existence of brackish conditions are detrimental to the breeding of cod, and involve loss of eggs and young fish. There can never be abundant cod supplies if the conditions are fatal to the depositing of eggs, and their development into fry.
Some sea fishes are able to endure a variety of conditions, such as extreme variations in temperature, salinity and specific gravity, and such fish as flounders and other flatfish, shad, alewives or gaspereaux, etc., can endure a wide range of such conditions. Shad and alewives, like salmon and sea trout, have indeed acquired the habit of migrating into fresh water for spawning purposes, but it is doubtful if typical sea fish such as flounders can really breed in fresh water. All observations tend to show that this is important, and even more emphatically does this apply to cod. It is a deep sea type of sea fish and for its food, and growth, and for favourable spawning, and life-development conditions, it must have the normal physical and chemical environment which the open sea provides, and it can only live and grow favourably in inlets or lagoons or shores of the sea where the salinities, specific gravity, temperature, &c., are those of the sea outside.
These conditions, as shown on the attached record of determinations by the Hydrographic Survey, are very unfavourable in Lake Melville.
(Signed) EDWARD E. PRINCE,
Dominion Commissioner of Fisheries.