BULLETIN NO. 94 Freshwater Vertdbrates of the Arctic and Subarctic BY V. C. WYNNE-EDWAHDS Aberdeen University, Scotland PUBLISHED BY THE JirISHERIES RESEARCH BOARD OF CANADA UNDER THE CONTROL OF THE HON. THE MIN1[STER OF FISHERIES "I TA.WA, 1952 'i� L�JI ____ �� ________ � BULLETIN NO. 94 Freshwater Vertebrates of the Arctic and Subarctic BY V. C. \VYNNE-EDWARDS Aberdeen Flliversity, Scotland PUBLISHED BY THE FISHERIES RESEARCH BOARD OF CANADA UNDER THE CONTROL OF THE HON. THE MINISTER OF FISHERIES OTT A \VA, 19.52 Printed in Canada by University of Toronto Press for the Fisheries Research Board of Canada CONTENTS INTRODUCTION 1 PHYSICAL CONDITIONS 2 THE FRESHWATER VERTEBRATE FAUNA 4 (A) Lampreys and Fishes 5 (i ) Petromyzontidae- Lampreys 5 (ii) ACipenseridae- Sturgeons 5 (iii) Salmonidae- Salmon, trout and char 6 Salmon (Salmo and Oncorhynchus) 6 Trout and char (Salvelinus, CTistivomer, H ucho and Brachymystax ) 7 (iv) Coregonidae- Whitefish, ciscoes, etc. 9 Inconnu and nelma (Stenodus) 9 Tullibee, "herrings" and ciscoes (Leucichthys ) 10 Whitefish (Coregonus) 12 Round whitefish (Prosopium) 16 (v ) Thymallidae- Graylings 16 ( vi) Osmeridae- Smelts 17 ( vii ) Catostomidae- Suckers 18 ( viii ) Cyprinidae-Minnows 18 (ix ) U mbridae- Alaska blackfish, etc. 19 (x) Esocidae- Pike 19 (xi) Percopsidae- Trout-perch 20 (xii) Percidae- Perch, pike-perch 20 (xiii ) Cottidae- Sculpins or bullheads 21 (xiv ) Gasterosteidae- Sticklebacks 22 (xv) Gadidae-Ling, burbot or methy 23 ( B) Amphibia 24 Northern wood frog (Rana Sylvatica cantabrigensis) 24 Northern swamp tree-frog (PseudacTis nigrita septentTionalis ) 25 (C) lvIammalia 25 White whale or beluga (Delphinapterus leucas) 25 Ringed seal (Phoca hispida) 25 Harbour seal (Phoca vitlllina ) 26 CONCLUSION 26 REFERENCES 26 INTR ODU CTIO N THE MAJORITY of vertebrates dealt with here are fishes. A few amphibia, but no aquatic reptiles, extend into subarctic regions; and of aquatic mammals, two species of seal and one cetacean Delphinapterus occur in arctic fresh waters. Semi-aquatic mammals, for example beaver Castor (circumpolar), muskrat Fiber (nearctic), water-rat Arvicola (palaearctic) , and otter Dutra (circum­ polar) , are excluded, together with numerous aquatic birds, many of them typically boreal and arctic, for example, loons (Gaviidae) , geese, swans and many ducks (Anatidae ). Roughly one-seventh of . the land area of the world drains into the Arctic ocean and adjacent ice-bearing seas, and many of the larger rivers have their sources far to the south in the temperate belt of Europe, Asia and North America. Five of them are two thousand miles or more in length, namely the Ob (2,700), Yenisei (3,300) , Lena (2,800 ), Yukon (2,000) and Mackenzie (2,525); and in summer they carry collectively an incalculable volume of relatively warm, usually mud-laden water to or beyond the Arctic circle, forming nahll'al channels for the dispersal of the temperate-zone continental aquatic fauna and flora into high latitudes. Within the area of Pleistocene glaciation in North America and Europe there is also a series of great lakes, the more northerly including Athabaska, Great Slave and Great Bear Lakes in the Mackenzie system, Nettilling and Amadjuak in Baffin Island, Ladoga and Onega in Russian Karelia; and because of impedi­ ments to drainage by glacial drift and permafrost, the frequency of smaller lakes and ponds is without parallel in other parts of the world. Parts of these freshwater systems either were covered by continental ice at some stage of the Pleistocene, so that their pre-glacial fauna was exterminated, or endured a climate so severe that few or no freshwater vertebrates survived. The post-glacial period, up to the present day, has been characterized, therefore, by recolonization of surprising speed and extent; and realization of this confers upon the study of the distribution of the freshwater fauna a deeper significance. Recolonization has, of course, taken place from refugia little or not at all affectedby glaciation. In North America, for example, the Mississippi basin is the most important; and in ,Asia several of the great freshwater systems, including Lake Baikal on the Angara-Yenisei, and probably the Ob, Lena and others, eVidently sustain an important part of their pre-glacial faunas. The spread of fishesfrom one river system to another has occurred in two ways : either through the sea' to enter the new river by its mouth; or through the headwaters,. where changes in the interior drainage, most commonly resulting from temporary block­ age by continental ice or glacial drift, have diverted the waters from one system into another. 1 The first method is generally possible only to fishes able to live either in the sea or in fresh water, that is "euryhaline" species; it appears to be the most frequent method of recolonization, and it has the result that these fishes are usually debarred from the upper waters of a system because they cannot ascend impassable waterfalls. The second method has been important where transitory dams of ice or boulder-clay have formed lakes draining now into one system, now into another, as has occurred so commonly in North America. The resulting alternation of isolation and communication is certainly connected with the origin of species­ s\v,umsin Salvelinus, Coregonus and Leucichthys (see below ) in some American and European lakes. As an agency of recolonization it has been successful to an unexpected degree; for example, it may have permitted the little trout-perch PCJ'copsis to pass, from the Great Lakes- �lississippi refugium, far to the north and west via the low-lying Canadian shield into the Mackenzie, and thence to its mouth, and over the (lowest) divide into the Yukon, where it was discovered by us in the Porcupine River at Old Crow, Y. T., in 1945. Percopsis may pOSSibly have had a second refugium during the Pleistocene in the far north-west, together with the only cyprinid now known in the Yukon, COHesius plumbeus, and several other fish, including the lake-trout Cristivomer, the round whitefish Prosopiurn cylindracewn, the northern sucker Catostornus catostomus, the black­ fishDallia, pike Esox lucius and burbot Lota lota. The northwestern distribution of Percopsis is restricted to a very narrow "route" which rather indicates present recolonization; in any case, however, whether this and the other species survived in one or in two isolated refugia, separated by two thousand miles, the repopu­ hUlon of the glaciated area has taken place with surprising rapidity. The most important families of arctic and subarctic freshwater fish contain many euryhaline species, for example, the sturgeons (Acipenser), salmon, trout and char (Salmonidae ), whitefish (Coregonidae ), inconnu (Stenodus ), smelts (Osmeridac ), sticklebacks (Gasterosteidae ), and sculpins (Cottidae ). The sea­ going SaZmo and Oncorhynchus, which enter fresh water only to spawn, have distributions centred on particular oceans, and may be divided into Atlantic and Pacific series; whereas the more strictly freshwater coregonines and others, which feed and grow freely in fresh water, belong rather to continental series, either palaearctic or nearctic as the case may be. It is interesting to find in the \!ackenzie and Yukon that, whereas the headwater colonists al=e of course American or nearctic types, several of the euryhaline al1adromous colonists are essentially palaearctic, including the inconnu and two or three coregonids. PHYSICAL CONDITIONS All the peculiar features of arctic freshwater habitats may be attributed to the effects of low temperature. Few or no cold-blooded vertebrates can survive the arctic winter except in fluid water; and the prevailing low summer temperature tends to retard growth and development. This retardation is to some extent compensated by adaptation, permitting faster growth at low temperature: thus Miller (1947, pp. 39-41 ) found little difference between the growth-rate of pike Esox lucius in Great Bear Lake and its growth-rate in Lesser Slave Lake 2 FIGUHE 1. The Arctic and Subarctic regions. An approximate southern boundary of the'lrea is indicated by the Northern Limit of Cereals (shown here by the fine dotted line; after Larousse's Atlas, Hachette, Paris). 10° further south; the same appeared to be true of whitensh. Coregonus and tullibee Leucichthys, but not of lake trout Cristivomer. The physical effects of temperature are somewhat different in running-water and standing-water environments, and these are treated separately. (a ) Several of the great rivers, as mentioned already, gather much of their water in temperate latitudes between 50° and 600N., where annual precipitation is higher than it is in the Arctic. In summer the upper waters are relatively warm, and during the two to four weeks required to carry these warm tributary waters down to the Arctic Ocean they retain their heat to an important extent. The Mackenzie, for example, may be inferred to have summer maxima in the main channel of the delta at 68°N. of 15° to 18°C., whereas in large lakes in the same latitude the temperature of the open water may never exceed 10°e. at the surface. Nansen (1914, p. 164 ) records a water temperature of 9.9°e. as late as September 7 in the Yenisei at 67°43'N. The great rivers are all characterized by extreme muddiness or turbidity, with the exception of about one hundred miles of the Mackenzie immediately below its outlet from Great Slave Lake, which serves as a mud-trap, and the Angara which similarly discharges the waters of Lake Baikal (Nansen, 1914, p . .305) . Visibility in the water is commonly less than 0.5 m., and this makes the habitat unsuitable for grayling Thymallus and freshwater trout Salt;elinus etc., which by habit take much insect food from the surface. The rivers are frequently several miles wide, shallow, and full of bars and alluvial islands. They also re­ semble one another in having remarkably even pronles, without falls or serious rapids to form barriers to shipping or migratory fish in their lower 1,000 to 1,500 miles.