64 



NORTH AMERICAN FAUNA 68 



completed a 180° reversal of course, and escaped before I could 

 pull the net from the water. 



DIVING 



Duration of food dives 



In water depths ranging from about 2 to 25 m. food dives were 

 timed with a stop watch from observation points on the cliffs of 

 Amchitka. Several factors render such observations somewhat 

 difficult to obtain and evaluate. Usually several otters were diving 

 for food in an area under observation. Although an otter may make 

 several food dives in a rather limited area, perhaps 15 m. in diam- 

 eter, the animal may unexpectedly move 100 m. or more beneath 

 the surface to a new feeding location. Also, a nearby otter may 

 move to the vicinity of an animal that is being timed, causing con- 

 fusion. The positive identification of the sex of a diving otter is 

 sometimes difficult to ascertain at the distances and with the 

 frequent poor visibility caused by weather conditions. 



General observations indicate that the duration of food dives 

 by adult males exceeds that of adult females. The following data 

 probably exaggerate this difference because the females' dives 

 were, to a greater extent than the males', in shallow water : 











Duration of food dives (seconds) 









Number 



Timed 



Average 











of animals 



food 



duration 



Maximum 



Minimum 







observed 



dives 



of dives 



duration 



duration 



Adult 



male 



4 



20 



100 



160 



72 



Adult 



female 



6 



41 



49 



82 



15 



The few observations presented are not strictly comparable, 

 because water depth varied and the animals under observation 

 may have had differing food preferences which caused some of 

 them to search longer for a particular item. Males feed on fish to 

 a greater extent than females. Among 50 stomachs of adult males 

 which contained food, 82 percent contained fish, and 62 percent 

 of 178 stomachs of adult females contained fish. The search for 

 and capture of fish would probably require more time than the 

 gathering of invertebrates. 



The best data on the duration of dives of the female were ob- 

 tained on 20 and 21 August 1955. On these two days a mated pair 

 of otters remained in a small cove at Amchitka and no other otters 

 fed in the area. During the period of mating the two otters dived 

 and emerged from their food gathering dives simultaneously. Be- 

 cause the male followed the female closely, the duration of her 



