to latitude, these animals have maintained their anadromous habits or have found shelter in 

 fresh waters. 



Along the Pacific coast, from Alaska to Oregon, the mighty elTort required to ascend the 

 rivers to the spawning grounds and the misery attending the return to the sea can well be under- 

 stood. The American salmon having gorged themselves in the waters of the ocean, and wearing 

 the silvery coat of pelagic fishes, migrate towards the fresh waters. Now their appearance 

 changes. Dark spots multiply over the skin, the belly turns pink or red and sometimes, as in 

 the humpback, a humj) of food reserves is formed on the back. The salmon then enters the 

 great rivers of North America ; the Yukon, the Skeena, the Fraser and the Columbia. They 

 make their way into these rivers much swollen with melted snow between banks lined by 

 centuries old conifers — into the gigantic heart of the Rocky Mountains. This journey is very 

 long and often exceeds 1,200 miles. During this time the fishes must struggle against the 

 currents to leap waterfalls before arriving at propitious gravel-strewn grounds in clear running 

 water. Now they pair and the females hollow out furrows with strokes of the tail and lay their 

 eggs in them. The males stay close to the spawn, immediately fertilise it and cover it with 

 fine gravel. At intervals of several minutes for two whole months the pair ceaselessly renew 

 their ellorts. When these amorous gambols come to an end the salmon are exhausted. Quite 

 inert, they passively drift down-stream towards the sea. But their battered bodies are attacked 

 by fungal diseases and in a marked state of decay they die as they drift, their bodies piling up 

 on the banks. Not one of them will see tlie Pacific Ocean again. 



Only the steelhead trout escapes this miserable death, just like the salmon of our country. 

 Renewing its strength in the sea it makes several journeys into the rivers during the course of 

 its life. 



These anadromous habits can be influenced by external causes, particularly when the 

 fishes withdraw on the eiuroachment of salty water over the continental shelf. But there 

 are also internal factors, which were revealed so clearly by Fontaine. These depend on variations 

 in the physiological condition of the organism and this is influenced by hormones from the 

 complex of endocrine glands. 



The banks of Newfoundland and the north. 



Between Nova Scotia and Newfoundland, the St. Lawrence River, the outfall of the Great 

 Lakes, emerges into a spacious bay and hollows oul a canyon right to the edge of the continental 

 shelf. This majestic river runs in an immense valley that once held a great glacier of eastern 

 America — a glacier which levelled down the Canadian landscape during many glacial periods. 

 Great areas of subsidence mark the limit of ancient rivers. The outlines of high places lying 

 under water have become " banks " separated by channels which represent fjords, and of these, 

 the thalwegs (or valley lines) are now found at a depth of about 50 fathoms. To the west of the 

 St. Lawrence channel extend the banks of Nova Scotia and Maine and towards the east the 

 Newfoundland Banks cover a submarine area nearly as large as France. The most westerly 

 bank is that of St. Peter, which carries over its northern part the islands of the old French 

 colony, Saint-Pierre-et-Miquelon. Then come Green Bank, Whale Bank and the Grand Bank, 

 with a summit (Ic Platier) rising to within 20 fathoms of the surface. 



.Ml these banks are covered by the polar waters of the Labrador Current, which arises from 

 the melting of the Great Ice Barrier after its break-up on the east coast of Greenland. Numerous 

 icebergs drift to the south in this current, which hugs the coasts of the United States. It is 

 subject to strong incursions of the Gulf Stream or Florida CurnMit, tliis bordering the .Vtlantic 

 transgression towards the east. This antagonism of cold polar and warm equatorial waters 

 takes much of the power from the two currents. The Labrador Current stops at Cape Hatteras 

 and the Gulf SI ream, having lost both speed and heat, dies away not far from the .Vzores, towards 

 40°W. This struggle has profound repercussions on the life of aninuds populating the Banks. 

 During a number of cruises in these regions I was able to discover the hydrological conditions 

 that are favourable ni- inaus|iiii()us for the cod-lishing. 



38 A freshly caught remoTa or shark-sucker. 



A tiger-shark (Galeocerdo) stranded on a beach in the 

 Comoro Islands. Photographs by J. Millot. 



