THE SEA OTTER IN THE EASTERN PACIFIC OCEAN 263 



hibited a degree of malocclusion caused by the growth of the 

 permanent postcanine teeth. In the early stages of eruption of the 

 permanent teeth, the deciduous teeth are pushed upward, so that 

 occlusion is impaired. When the deciduous teeth are finally lost, 

 the permanent teeth are still below the level of adjacent teeth 

 (see Dentition). Adults having poor teeth comprised 78 percent 

 of the total found dead. The attrition of teeth appears to be an- 

 other result of the reduction of soft-bodied invertebrates. Hard- 

 shelled organisms are probably eaten to a greater degree by this 

 crowded Amchitka population than in less densely populated areas. 

 Animals having good teeth not only compose a minority (17 per- 

 cent) of the dead adults on beaches but healthy adults spend less 

 time on shore (as indicated by animals captured there) during 

 periods of storm surf than do emaciated juveniles and old adults. 



Weather and sea conditions 



In the fall of 1959, the U.S. Weather Bureau began to record 

 weather conditions in the outer Aleutian Islands. Before this time, 

 no such records were available. Thus, during the 21 January to 

 20 May 1959 study period I kept a daily record of weather con- 

 ditions. These data demonstrated that the increased mortality 

 coincided with the period of greatest storm activity. 



Complete weather records are now available for the years after 

 1960. These data were recorded at Shemya Island, which is 200 

 miles west of Amchitka, but radio reports of weather at Shemya 

 received while I was on Amchitka indicated that a few hours after 

 weather conditions were reported at Shemya similar weather 

 reached Amchitka. The annual cycle of weather conditions in the 

 outer Aleutians is quite uniform. 



The average seasonal mortality observed on Amchitka from 

 1955 through 1963 and the mean monthly wind velocities recorded 

 1960 through 1963 are shown in figure 102. This graph demon- 

 strates that the period of greatest mortality, when 75 percent of 

 the annual mortality occurs, coincide annually with the period of 

 maximum wind velocities in the late-winter, early-spring period. 

 It also shows that the period of least mortality occurs during the 

 summer period of minimum wind velocities. In the fall, when the 

 season of storms begins, a slight increase in mortality occurs. 

 Most animals, however, emerge from the summer, early-fall period 

 in good physical condition and the mortality remains low until 

 after a period of sustained stormy weather reaches a peak in 

 March. 



The general coincidence of high mortality and stormy weather 



