HARD SUBSTANCES EATEN BY SEALS. 65 



The most frequent feeding grounds, as indicated by tbe logs of pelagic sealers, lie 

 from 75 to 150 miles to the southward and eastward and to the northward and west- 

 ward of the Pribilofs, some little distance outside the 100-fathom line, or where the 

 bottom of the sea dips abruptly downward from 500 to 5,000 feet. Few seals are 

 taken or recorded in the comparatively shallow waters to the north and east of the 

 seal islands, and although there are some indications that a portion of the herd fre- 

 quents this region during the summer, yet the map giving the distribution of the seals 

 ill August and September is practically a map of the feeding grounds. 



An examination of the chart will show that there seems to be a direct relation 

 between the 100-fathom line and the localities where the seals obtain food, but the 

 conditions affecting the feeding grounds can only be learned from a long and careful 

 study of the depth and temperature of the water and set of the currents, since these 

 are the prime factors in determining the presence and distribution of the minute 

 plants and animals, which may be called food units, and on which all higher animal 

 life ultimately depends. 



As the principal feeding grounds, large as they are, seem to lie within certain 

 more or less definite boundaries, it follows that in going to feed the traveling seals do 

 not radiate from the islands like the sticks of a fan, but go and come in parallel lines 

 or lanes. Still, it should be borne in mind that our knowledge of these points 

 depends on the catch of sealers on certain known dates, and the movements of the 

 sealing fleet are largely determined by the catch of a few vessels, since if A and B 

 know that C is taking seals they and others do not like to leave the vicinity, leaving 

 a probability for a possibility. 



From the condition of the contents of the stomachs it is apparent that everything 

 is swallowed entire, a pollock 18 inches long being bolted, head and all. This is 

 evident from the fact that the bones of the head are always present when the quan- 

 tity of bones is large, but they may be regurgitated, together with the other bones 

 of the anterior portion of the body, leaving only the tail vertebrae. 



The indications are that digestion is extremely rapid, since even on the feeding 

 grounds it is almost impossible to obtain stomach contents sufficiently well preserved 

 to admit of identification from external characters. Hard parts — such as fish bones, 

 the beaks and crystalline lenses of the eyes of squids — are regurgitated somi'thing 

 after the manner in which the skin and bones of mice are ejected by birds of prey. 

 In this manner the seals also eject the small i)ebbles and other hard substances, such 

 as shells and bones, whi(;h they swallow for problematical purposes; and it is by this 

 method that the sea lion must get rid of the stones, sometimes of large size, which it 

 swallows in considerable quantities. There are plenty of theories as to why these 

 things are swallowed by seals, the most reasonable of which is that they are to aid 

 digestion by grinding up such substances as fish bones and the hard parts of crabs. 

 But while this seems plausible enough when applied to the sea lion, which eats many 

 crabs and swallows quantities of stones, some weighing 2 or 3 pounds, it fails with 

 the fur seal, as this animal is not known to feed upon Crustacea, and the pebbles found 

 in its stomach are of small size and not mixed with food. The stomachs of nursing 

 pups are quite as liable to contain pebbles as are those of adult seals, but in this case 

 they are probably swallowed instinctively. On August 20 a pup was seen meandering 

 about Lukanin, stopping now and then to pick up a pebble; and on the same date a 

 pup, full of milk, was killed in the water whose stomach contained 13 large and 2G 

 5947— PT 3 5 



