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No. 1034.

HAMILTON INLET

OBSERVATIONS ON THE FAUNA AND FLORA.
By C. TATE REGAN, M.A., F.R.S., Keeper of Zoology in the British Museum (Natural History).*

1.—SALINITY OF WATER IN HAMILTON INLET.

Dr. Kindle's report on the fauna and flora of the Hamilton Inlet is so incomplete that, in order to arrive at any conclusion, it is necessary to consider the conditions in this area, and what happens in similar conditions elsewhere. As regards the salinity of the water there are available, for the inner part of the Inlet, west of the Narrows, the salinity determinations made by the Canadian Hydrographic Survey in September, 1921. The salinity of the surface water was determined at five points, at which the figures found (10·57 to 15·57) have been inserted on the chart (fig. 3, p. 4 ; the salinities at various depths were also determined, and I have attempted to represent the results obtained by means of a diagrammatic vertical section, which is, so far as concerns the region west of the Narrows, based entirely on these determinations.
There are also a number of determinations of the density or specific gravity of the water, of which those made in 1923 are summarized by the Senior Tidal and Current Surveyor (C. pp. 2333-4). This gentleman writes of water having a density of 13 per cent., 21 per cent., etc., of that of sea-water, but as the density of fresh-water (1·000) is 97·6 per cent. that of the sea-water taken as a standard (1·024) this is obviously a mistake alternatively he writes of water with a certain percentage of sea salinity, but the percentage system does not give true values for salinities. Sir John Murray (The Ocean, p. 54) gives the figures of specific gravity at 60° F. corresponding to salinities of 0, 10, 20, 30, 32·5, 35, 37·5 and 40 per 1,000. I have plotted these and connected them by a line, to form a diagram by means of which the specific gravity determinations can be converted into approximate salinities (fig. 1, p. 2).
It will be noted that compared with the salinity of water of specific gravity 1·024, the salinity of water with specific gravity 1·006 is not 25 per cent., but 31 per cent., and that of water of specific gravity 1·012, not 50 per cent., but 55 per cent.

*This report has been prepared by me in my time and in my private capacity as a zoologist who has studied problems of distribution; it must not be considered to represent an official view.—C. T. R.

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Taking the region west of the Narrows it will be seen that the density determinations made in July and August, 1921 (C. p. 1946) confirm the salinity determinations made in September, corresponding to surface salinities of ca. 15 at Pelter's Cove and 8 miles west of Caravalla Point, ca. 10·8 in Mulligan's Bay. Those of surface water made on August 21st and 22nd, 1923, are lower (e.g., salinity ca. 9 instead of 14 off St. John's Island), but the drop at Rigolet from S.G. 1·0205 (flood) and 1·0168 (ebb) on August 17-18 to 1·0170 (flood) and 1·0125 (ebb) on August 26th is sufficient indication

FIG 1.—Diagram showing the relation between salinty and specific gravity at 60° F.
that heavy rainfall was responsible for this. The general average of the density determinations in the Narrows justify the figure 23 on the map, indicating the approximate average salinity of the surface water at about that point ; the exact location at the surface of the figures 26 and 28 is unimportant.
No doubt the salinity of the water in Hamilton Inlet would be higher during the winter, as in the Norwegian fiords ; in these, melting snow and ice and rainfall swell the rivers and produce a surface layer of water of low salinity during the summer ; but in the winter this layer tends to disappear and the surface water has a much higher salinity.

HYDROGRAPHY OF THE BALTIC

The account given by the Canadian hydrographers recalls the conditions in the Baltic, where we have also the decreased range of the tides, the lowered
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FIG. 2.—Baltic Sea (after Petterson)—

(A) Chart, showing average salinity of the water at the surface.
(B) Vertical Section, showing the salinity of the water at different depths.

p. 2512

FIG. 3.—Hamilton Inlet. Chart and Diagrammatic Vertical Section. In the chart the salinity of the surface water at different points is indicated, and the 50 fathom line (approximate) has been inserted. The section represents the salinity of the water below the surface.

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salinity, the fresher water at the surface and the salter water below, the outflow greater than the inflow, etc. The hydrography of the Baltic has been described by Petterson (Scottish Geographical Journal, 10, 1894), who states that it receives by rainfall and rivers much more water than it loses by evaporation ; hence there is a surface current outwards and the surface water is fresher than that nearer the bottom ; his chart and diagrammatic representation of the salinity of the water (fig. 2, p. 3) may be compared with those given for the Hamilton Inlet ; the lesser salinity of the Baltic is very evident.

FISHES OF THE BALTIC.

The Baltic is a marine area, with a marine fauna and flora. Such typically marine fishes as herring, sprat, garfish, cod, plaice, turbot, sandlaunce, lump-sucker, gobies, etc., are widely distributed in the Baltic and are permanent residents ; in some years mackerel enter the Baltic in large schools and may range to the Gulf of Finland. There are other marine fishes such as whiting, gurnard, brill, sole, etc., that inhabit the southern Baltic, and others again that are found only in the south-west corner. The number of species of fishes resident in the Skaggerack that never enter the Baltic is relatively small. The cod ranges to the lower part of the Gulf of Bothnia, where the salinity of the water at the bottom is about 7. This fish is the object of extensive fisheries. The capture of spawning fish, and modern investigations of the distribution of the eggs and larvae, leave no room for doubt that the cod breeds in the Baltic (cf. Strübberg, Medd. Komm. Havunders. Fiskerei, VII, No. 1, 1922).
Some marine fishes enter fresh-water to breed, or for other purposes ; these may form freshwater colonies—which in time may become fresh-water species of marine genera ; but the great majority of the fresh-water fishes of the world belong to families that are restricted to fresh-water. There are many species of such true freshwater fishes, pike, roach, dace, perch, etc., in the countries round the Baltic. Several of them extend into the fresher parts of the Gulfs of Bothnia and Finland and into the slightly saline water inside the island belt off the coast of Sweden. The perch is generally considered to be most tolerant of some salinity of the water, and on the east coast of Sweden it is found not only between the mainland and the island belt, but sometimes outside the island belt.
In Mr. Prince's memorandum it is stated that the specific gravity of the water in Lake Melville is such as to prevent cod eggs from floating or to enable them to develop normally. It is also stated that cod eggs and fry find favourable conditions in water with specific gravity 1·021, and that if the specific gravity be reduced to 1·019 nearly the whole of the eggs sink to the bottom. The breeding and development of the cod in the Baltic require some explanation in face of these statements. Mortensen in 1897 discovered that in the Baltic the eggs of the sprat were 1·2 to 1·5 mm. in diameter and had a specific gravity of 1·006 to 1·007, whereas in the Limfiord they measured 0·9 mm. and had a specific gravity of over 1·017 ; he regarded


[1927lab]



 

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