The exposed parts of the stumps were par- 

 tially encrusted with living organisms such as 

 coralline algae, bryozoans, and sponges, but 

 much of the exposed wood surface was barren of 

 organisms. There was no visible evidence of any 

 biological degradation of the wood, that is, no 

 borer holes or indication of decay. The surfaces 

 of the wood appeared to be shaped principally 

 by mechanical weathering or erosion. Unlike 

 new wood exposed in a marine environment, the 

 wood of the stumps appears to have been 

 immune to the usual attacks of wood-boring 

 organisms. During the period of total encase- 

 ment in the rock substrate, the wood probably 

 underwent chemical changes that resulted in 

 immunity to biodegradation. 



As stated earlier and as shown in Figure 4, 

 the substrate in direct contact with the stumps 

 was undisturbed bedrock. Rock samples we 

 obtained from fresh rockfalls along the cliff face 

 containing the stumps were identified as coming 

 from volcanic breccia of the Chitka Point For- 

 mation of the Miocene age (L. M. Gard, pers. 

 comm.). The Chitka Point Formation is com- 

 posed of subaerial lava flows, breccias, tuffs, 

 and conglomerates derived from a volcano 

 which must have been located on western 

 Amchitka and eastern Rat Islands (Carr et al., 

 1971; L. M. Gard, pers. comm.). Potassium- 

 argon dates obtained on lavas of the upper part 

 of the Chitka Point Formation indicated an age 

 of at least 12.4± 1.1 million yr (Carr et al., 1971). 



Amchitka and all of the Aleutian Islands are 

 now devoid of naturally occurring trees. Evi- 

 dence that trees once grew on Amchitka does 

 exist, however. During Miocene time, trees and 

 other carbonaceous material were often incor- 

 porated into volcanic mudflows and debris flows 

 of the Chitka Point Formation, as evident by 

 the presence of this material in many of the out- 

 crops of breccias, tuffs, and conglomerates along 

 the Bering coast of Amchitka (Powers, Coats, 

 and Nelson, 1960; L. M. Gard, pers. comm.). 



The significance of the tree stumps reported 

 in this paper derives from their in situ location 

 23 m below present sea level. Because of the off- 

 shore and submerged location of these stumps, 

 they represent a time when the island was not 

 only forested but larger and at least 23 m higher 

 in relation to sea level. 



Acknowledgments 



L. M. Gard, Geologist, U.S. Geological Survey, 

 assisted by supplying background information 

 on the geologic history of Amchitka Island and 

 by reviewing a draft of this manuscript for 

 accuracy and aptness of interpretation. Theodore 

 R. Merrell, Jr. assisted in the fieldwork and in 

 the preparation of this report. 



Literature Cited 



Carr, W. J., L. M. Gard, G. D. Bath, and D. L. Healey. 



1971. Earth-science studies of a nuclear test area in 

 the western Aleutian Islands, Alaska: An interim 

 summary of results. Geol. Soc. Am. Bull. 

 82:699-705. 

 Powers, H. A., R. R. Coats, and W. H. Nelson. 



1960. Geology and submarine physiography of Am- 

 chitka Island, Alaska. U.S. Geol. Surv. Bull. 

 1028-P:521-554. 



Louis Barr 



Robert J. Elus 



John H. Helle 



Auke Bay Fisheries Laboratory 



National Marine Fisheries Service, NOAA 



Auke Bay. AK 99821 



ESTIMATION OF RATES OF TAG 



SHEDDING BY NORTHWEST ATLANTIC 



BLUEFIN TUNA> 



A joint experiment was initiated by the Fisheries 

 Research Board of Canada (FRBC), the Na- 

 tional Marine Fisheries Service, and the Woods 

 Hole Oceanographic Institution (WHOI) in 

 1971 under the leadership of F. Mather to 

 estimate the rates of tag shedding by bluefin 

 tuna. Five hundred and eighty bluefin tuna 

 were double tagged with one of four types of 

 dart tags off the east coast of the U.S. during 

 the 1971 fishing season. Two types of darts, 

 metal and plastic, were used and tags supplied 

 by FRBC were slightly different from tags sup- 

 plied by WHOI. Tags and tagging procedures 



I Contribution No. 3010, Woods Hole Oceanographic 

 Institution, Wdods Hole, MA 02543. 



1103 



