mainly Arctic Cod. Boreogadus saida (table 

 V). The methods used by various predator 

 species to capture their prey, and the depths at 

 which they feed, differ (table VI), so that they 

 may not be in competition for the same food 

 resource. It is not known, however, whether 

 predation by higher vertebrates constitutes a 

 significant factor that might limit populations 

 of invertebrates and fish in the Chukchi (Quast 

 in preparation). 



ABUNDANCE 



We have not yet attempted to convert our 

 line transect counts of the birds and mammals 

 we observed into estimates of total population. 

 Such estimates from line transect data of at- 

 sea observations are frought with hazards 

 (Yapp 1955, Bailey 1966). The major prob- 

 lems are the near impossibility of estimating 

 distance from a moving ship and the diflferen- 

 tial visibility of various species. For instance, 

 a Walrus or seal on a cake of ice is visible at 

 a greater distance than one in the water. A 

 single adult Ross' Gull flying is far more difl^- 

 cult to see than a Glaucous Gull or a flying loon. 

 Small auklets may be virtually invisible when 

 swimming in rough water, but are conspicuous 

 during flat calms. This makes both our counts 

 of birds seen, and any estimates of birds per 

 unit area based on them, somewhat suspect. 

 Secondly, in order to convert line transect data 

 to absolute density, one needs to assume that 

 birds are distributed at random. This is pre- 

 sumably so for species that pay little attention 

 to ships, such as alcids or loons, but is not so 

 for birds that are attracted to ships or follow 

 in the wake, such as gulls. We used only the 

 largest count of gulls on each station or each 

 20-minute transect interval for just this rea- 

 son. The same is true if the environment is not 

 uniform as in the study area where some 

 species were more common near shore than far 

 out at sea, while others congregated near ice. 

 Migrating flocks passing through an area, like- 

 wise, do not constitute random distribution. 

 Some of the large flocks of Oldsquaw and eiders 

 that we saw were probably migrating and were 

 a part of the local population one hour and 

 gone the next. Good statistical methods have 

 not yet been devised to account for all of these 

 variables. 



On the other hand, it should be possible to 

 compare line transect counts made under 

 similar environmental conditions at different 

 times in the same area in order to obtain esti- 

 mates of relative abundance in different sea- 

 sons (.see also Bailey 1966, appendix). One can, 

 therefore, compare abundance between species 

 such as the Kittiwake and Ross' Gull, or be- 

 tween areas. Such analyses are being pursued 

 by DivokJ^ 



At any rate, it is apparent that considerable 

 numbers of birds and mammals of some species 

 are present in the Chukchi Sea at this time of 

 the year. A significant fraction of the world 

 population of Ross' Gull probably migrates 

 through or winters in the Chukchi. We saw 

 numerous large pods of Walrus. In one re- 

 stricted area we are sure that over 500 were 

 present (October 4) because we saw almost all 

 of them at the same time. Estimates of the 

 combined total population of Pacific Walrus, 

 both Siberian and Alaskan (0. r. divergens) 

 range between 30,000 and 70,000 (King 1964, 

 Johnson et al, 1966). Our observation that day, 

 therefore, may have included between 1/60 and 

 1/140 of all the individuals of the subspecies in 

 the world. 



The resident populations of birds and mam- 

 mals in the Chukchi may be neither large nor 

 concentrated, except in inshore waters or near 

 the cliffs at Cape Lisburne during breeding. 

 On the other hand, the Chukchi serves as an 

 important migratory pathway for the marine 

 species and many ducks, geese, and shorebirds 

 that breed east of Point Barrow and migrate 

 to the Bering Sea or Pacific Ocean. In addition, 

 it serves as a temporary post-nuptial feeding 

 ground for some species that breed further 

 south. Even during September and October we 

 found that considerable numbers of some 

 species of marine birds and mammals were 

 using the area and we conclude that large scale 

 pollution in the area, in any season, could have 

 an important effect on the higher vertebrates. 



ACKNOWLEDGMENTS 



We are grateful to the Oceanographic Unit 

 of the U.S. Coast Guard and its director Dr. 

 Merton C. Ingham, for extending the invitation 

 for our participation in WEBSEC-70. We are 

 indebted to Capt. Theodore L. Roberge, the 



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