MIGRATIONS OF WHALES — KELLOGG 469 



food for the sei whale {Balmnoptera horealis). The stomach con- 

 tents of several sei whales (Collett, 1886, p. 261) killed off East Fin- 

 mark in July consisted entirely of the copepod, Galanus fimnarchi- 

 cus, but along West Finmark they were feeding on euphausids. The 

 bowhead often feeds on pelagic mollusks (Lilljeborg, 1866, p. 308) 

 such as the pteropods, Clio and L/'macina, in addition to copepods of 

 the genus Calanus. 



While the available data seem to indicate that the migrations 

 of whales are governed to some extent at least by the plankton 

 supply and hydrographic changes, their annual journeys take them 

 to localities favorable for reproduction and growth of young. It 

 is also possible tliat the food prerequisites of any given area may 

 remain favorable, but that the whales for some inexplicable reason 

 have gone elsewhere. The seasonal north and south migrations 

 may also under certain conditions extend east and west. If this is 

 confirmed, the fact will further complicate the study of the biology 

 of these pelagic mammals. 



The underlying causes for the marked seasonal fluctuations in 

 the abundance of whales on many of the whaling grounds is little 

 understood at present. By tracing the movements of waters sur- 

 rounding the feeding grounds of whales it may be possible to dis- 

 cover the physical and biological factors that regulate these fluctua- 

 tions. Oceanographic investigations have repeatedly shown that 

 there is a direct connection between the physical and biological 

 conditions of the feeding grounds and the presence or absence of 

 pelagic animals. It has been shown that there are certain mass 

 movements of water which may alter any set of conditions. The 

 chemical content of sea water varies from time to time and from 

 place to place according to the influence of ocean currents and ocean 

 drift. Sufficient quantities of certain kinds of food necessary to 

 support the long-continued presence of large numbers of whales 

 require favorable hydrographic conditions. An excellent illustra- 

 tion of the influence of hydrographic factors on the propagation of 

 plankton is brought out by the observations of Hardy (1928, p. 

 771) in the vicinity of South Georgia. 



It is generally accepted that ocean currents result from differences 

 in the specific gravity of water, and that masses of water will flow 

 from the place where it is relatively light to another region where 

 it is proportionately heavy. Prevailing winds, rotation of the earth, 

 and tides also exert an influence on the movement of masses of water. 

 Some of these currents are cold and others warm. Physical differ- 

 ences such as salinity and temperature make oceans a complex of 

 water masses. Observations have shown that there is an upper layer 

 of cold fresh water and a lower layer of salty water at the entrance 

 24034—29 31 



