Xo. 499 J 



NOTES AND LITERATURE 



493 



barrier between the American and European eels (AnguUla 

 cJn-ijspa and A. nihjaris > . Eels of European streams approach- 

 ing sexual maturity and migrating seaward must travel to the 

 edge of the continental shelf to reach suitable spawning grounds. 

 The Baltic and North Seas are too shallow, and waters to the 

 west of Norway are deep enough but their temperatures are 

 too low. 



The eels, as they migrate, undergo a considerable change in 

 appearance, passing from the stage known as the yellow eel to 

 that of the silver eel, in which feeding is suspended, the digestive 

 tract is shrunken and sexual glands show some enlargement. 

 The direction of migration in the Baltic in the autumn is out 

 toward the open sea. The paths of migration are usually paral- 

 lel to the coast and in shallow water, though eels have been known 

 to cross channels 60 meters in depth. The direction and rate of 

 migration was worked out by Dr. C. G. Joh. Petersen, the director 

 of the Danish Fisheries Laboratory, by means of marked fish. The 

 rate of movement in the migratory season is about 15 kilometers 

 per day. The eels in these shallow waters, where their presence 

 is revealed by commercial fishing, are none of them sexually 

 mature. Their further movements are unknown but the pre- 

 sumption is that they continue their course toward the open sea 

 and to the edge of the continental shelf. A single capture in 

 the English Channel twenty miles from land confirms this con- 

 jecture, as do also the captures made by Grassi and Calami ruccio 

 in the whirlpools at Messina, where occasional specimens of the 

 common eel are brought to the surface, which differ materially 

 from those taken in shallow waters. They are silver eels in 

 which the breeding dress is further accentuated by darker color, 

 the anterior border of the gill openings and the pectorals become 

 an intense black, the eyes also become enormously enlarged and 

 the sexual organs show greater maturity. Maturing eels have 

 also been taken from the stomachs of the sword-fish and in the 

 collection of Prince Albert of Monaco is a large eel taken from 

 the stomach of the cachelot. These facts in conjunction with 

 certain testimony on the part of fishermen suggest the possibility 

 of a pelagic or bathypelagic habitat of the eel in its migration 



