June 13, 1878] 



NATURE 



171 



able,r\vhen the approach of winter makes the fishing 

 industry of the Dominion coasts hazardous or impracti- 

 cable, to start at once for the southern grounds, where 

 they can pursue their calling through the winter months. 

 This is so great an advantage, that it frequently renders 

 a northern summer fishery remunerative, which would not 

 be so if the fishermen were dependent upon it alone. 



The fish which frequent the United States coast-waters 

 south of the 39th parallel are chiefly of the "anadro- 

 mous" kind — that is, they live for most of the year in the 

 sea, where they attain the greatest part of their growth, 

 running up into fresh waters for the purpose of spawning. 

 The chief among these are the shad, the alewife or fresh- 

 water herring, the rock-fish, and the striped bass. On 

 the other hand the "commercial " fishes — the cod, her- 

 ring, haddock, hake, halibut, and mackerel — are found 

 in greatest abundance where the temperature is kept 

 down by the Arctic current, which at the same time fur- 

 nishes their great store-house of food, and the temperature 

 congenial to them. On the fishing banks of the open sea, 

 th e abundance of hake and cod depends essentially upon the 

 resort of herrings; but it is by the "anadromous" fishes 

 that the cod is attracted in-shore. And the destruction 

 of the cod-fisheries which formerly existed on the 

 New England coast is attributed by the United States 

 Fisheries' Commission to the comparative annihilation of 

 the " anadromous " species, through the obstruction and 

 contamination of the river-waters by the various land- 

 industries established along their banks. Below the 

 39th parallel, however, the "anadromous" fishes find 

 an accessible winter' s home in the warm water off the 

 coast of the Southern States, and enter its rivers to 

 spawn as early as February, The United States fisher- 

 men being privileged to follow them thither, are thus 

 placed in a position of great advantage as compared with 

 those of the Dominion ; the enterprise of the former 

 being stimulated, while that of the latter is cramped, by 

 the Fishery-clauses of the Treaty of Washington, which, 

 as Mr. Hind points out, " place an obstructive boundary 

 on the operations of the British-American fishermen far 

 more limited and confined than formerly existed under the 

 Reciprocity Treaty, while in the same breath they remove 

 every impediment to perfect freedom of action to the 

 United States fishermen throughout an area of great 

 productiveness and practically unlimited extent." 



The Physical conditions under which marine life exists 

 on the coasts of British North America, differ in this 

 important particular from those which prevail in the 

 seas of Northern Europe — that while the great modify- 

 ing influence of the latter is the warm N.E. flow, popu- 

 larly known as the Gulf Stream, the former are chiefly 

 dominated by the Arctic Current, which brings down 

 glacial sur/ace-\iAiQr from the coasts of Greenland and 

 Labrador. The existence of a low bottom-ttm'peratnre, 

 wherever the basin is deep enough to admit the Arctic 

 under-flow, is common to both : but while, on the European 

 side — to take as an example what I have called the 

 " Lightning" channel that lies N.E. and S.W. between 

 the Orkney and Shetland Islands and the Faroes — the 

 glacial under-flow from the N.E. is overlaid by a com- 

 paratively warm upper-flow from the SuW., on the 

 American side the glacial under-flow from the N.E. is 

 overlaid by a cold upper-flow from the same quarter, urged 

 southwards by the prevalence of northerly winds along 

 the Greenland and Labrador coasts. And alike in the 

 upper and in the under south-moving strata is there a 

 westerly tendency (caused by the deficiency of easterly 

 momentum which they bring from latitudes higher than 

 60° into lower parallels) which causes them both to "hug 

 the shore " along the whole coast-line not only of British 

 North America, but of the United States. The super- 

 ficial Arctic wind-current cannot be distinctly traced 

 further south than New York ; but none the less is there 



a band of cold Avater intervening between the coast-line 

 of the Southern States and the Gulf Stream; and the 

 Challenger soundings have distinctly shown the con- 

 tinuity of this band with the deep Polar under-flow which 

 underlies the Gulf Stream, and surges up on the western 

 slope of the Atlantic basin. 



The course not only of the superficial Arctic current, 

 but probably also that of the deep under-flow, is greatly 

 modified by local conditions ; that of the former chiefly 

 by the strong tides and local winds of the coast, especially 

 in estuaries, straits, or inlets ; and that of the latter by 

 variations in depth — the effect of a shallowing bottom 

 being to bring the cold under-flow nearer to the surface. 

 And thus, as Mr. Hind observes, the extraordinary varia- 

 tions which present themselves on the Dominion Coasts 

 are specially worthy of study in their relation to Fish-life. 

 No such peculiarity is more remarkable, than that which 

 seems almost constant in the Strait of Belle Isle, sepa- 

 rating the north end of Newfoundland from Labrador ; 

 for here, in the latitude of London, the sea has a glacial 

 temperature all the year round. Pack-ice remains in 

 these Straits through the early summer, with a compara- 

 tively high air-temperature ; and they are never clear of 

 bergs. Sometimes the surface freezes over again at 

 Midsummer after the breaking up of the winter ice. In 

 1873 the surface- temperature of the sea in these Straits 

 on four consecutive days in the latter part of June was 

 found to range from 36° to 28° ; the air-temperature 

 during the same time ranging between 43° and 68°. The 

 extremely little influence which this comparatively high 

 air-temperature' had upon the temperature of the surface 

 water, clearly shows that the latter must be constantly 

 kept down by melting ice, and also by the surging-up of 

 the deep glacial underflow. Numerous cases are cited by 

 Mr. Hind of the influence of winds and tides in lowering 

 the surface-temperature by mixing the deep cold stratum 

 with the superficial ; the general rule being that easterly 

 sea-winds generally raise the temperature of the surface- 

 water, while westerly winds cool it. That such changes 

 (as from 52° to 38° in a single day) have no relation to the 

 temperature of the winds themselves, is clearly shown by 

 comparative observations of the sea- and air-thermo- 

 meters ; the moist easterly sea-winds being generally 

 colder (at least during summer) than the dry winds crossing 

 from the land ; while the influence of a shoaling bottom,, 

 lying in the course of the deep glacial flow, is shown by a 

 sudden descent of the surface-temperature to 33°. So, 

 again, a mixing of the different strata produced by cur- 

 rents along the shoaling waters of the Labrador coast, 

 particularly among the islands, rapidly reduces the tem- 

 perature ; so that, in a cold calm after a storm in 

 December, all the conditions are present for that forma- 

 tion of "anchor-ice," of which Mr Hind gave an account 

 in a former communication. " The sea on the shoals is 

 uniformly cooled ; a clear sky and a north wind assist the 

 radiation of heat ; and ice-spicules form with great 

 rapidity in the Labrador current, often increased in local 

 intensity by tides." It has been lately stated, on the 

 authority of Prof. Mohn, as a fact well known to the 

 Norwegian fishermen, that the deep water is often so cold 

 that it freezes if disturbed, although it continues liquid so 

 long as it remains perfectly still ; fishes passmg into such 

 a glacial stratum being frozen, and coming to the surface 

 as lumps of ice. 



Mr. Hind draws attention to a remarkable series of 

 observations of temperature and specific gravity, taken 

 by Dr. Kelly, of Quebec, during the Admiralty Survey of 

 the Gulf of St. La'wrence in 1830-36; which show that a 

 very curious temperature-stratification exists in that vast 

 estuary, obviously produced by the mixing of the great 

 body of fresh water brought down by the river St. Law- 

 rence with the cold Labrador current. A zone of water 

 of a certain degree of warmth is superimposed upon a 

 zone sometimes of lower and sometimes of higher temper- 



