December 27, 1912] 



SCIENCE 



897 



The ground also presents difficulties. Long 

 stretches of unstable bowlders are interspersed 

 with jagged lava potholes. There are cinder 

 slopes and basaltic benches. In places the 

 rocks are worn smooth as glass by the fric- 

 tion of innumerable seal bodies and the 

 bowlders near the water line are always treach- 

 erous with slime and slippery sea growths. 

 Over all is the unspeakable Bering Sea 

 weather— without sunshine and alternating 

 between thick and thin fog accompanied by 

 rain, flying spray and howling wind. 



The result, however, repaid the effort. 

 For the first time the breeding stock of the 

 herd has been brought within the range of 

 exact figures. The herd is shown to be in bet- 

 ter condition than was expected. Its recup- 

 eration will be more rapid. The splendid 

 body of pups disproves absolutely the conten- 

 tion which has recently played so important a 

 part in discussions of the herd's condition, 

 namely, that the stock of breeding males has 

 been reduced too low or become invirile and 

 impotent through the operations of land kill- 

 ing. The immediate response of the herd to 

 its release from the drain of pelagic sealing 

 as certainly proves this to have been its sole 

 cause of decline. 



George AEcnrBALD Clark 



U. S. BuEEAXJ OF Fisheries, 

 St. Paul Island, Alaska, 

 August 31, 1912 



TSE FUB SEAL MORTALITY OF TEE 

 PBIBILOF 1.00KEEIES IN TEE AB- 

 SENCE OF FELAGIC SEALING^ 

 The breeding season of 1912 for the Pribi- 

 lof fur seal was the first in many years un- 

 affected by pelagic sealing. The herd has 

 promptly responded to the removal of this de- 

 termining check to its increase. The deaths 

 on the rookeries reflected not only the arrest 

 of pelagic sealing but the drop in the rate of 

 natural mortality which has been much more 

 rapid than the rate of decrease of the herd. 

 The question of mortality was investigated in 

 1896 and 1897 by the Fur Seal Commission, 



^Published by permission of the Commissioner 

 of Fisheries. 



and during the past season by the writer, the 

 death of the young being the chief concern 

 in both cases. The loss during the entire sea- 

 son, until the migration of the cows and pups 

 late in the fall, has never been covered, but 

 the major portion occurs earlier and indicates 

 the proportions of the mortality from natural 

 causes. In 1896 and 189 Y, putting aside the 

 heavy loss from pelagic sealing by using only 

 the data prior to August 15, the approximate 

 date on which starvation caused by the pelagic 

 catch began to be fatal to the young on the 

 rookeries, the two chief causes of mortality of 

 pups were uncinariasis (hookworm disease) 

 and natural starvation, the former leading and 

 placing a heavy incubus on the herd. The 

 seal mother bears a single pup each year, and 

 will nurse no other than her ovm offspring. 

 Pelagic sealing therefore caused the starva- 

 tion of the young by an artificial interference 

 with the herd, while natural starvation is due 

 to accidental deaths of females which have 

 nursing pups and probably also to their fail- 

 ure to find their offspring after returning 

 from trips to sea. It was estimated at 30.8 

 per thousand in 1896. The total loss from all 

 causes in 1896 before the middle of August 

 was about 90 per thousand. 



The data obtained in 1912 make necessary 

 some readjustment. The total natural loss to 

 August 22 on St. Paul Island is 880, or 12.5 

 per thousand. From starvation to the middle 

 of August a death rate of 4.3 per thousand is 

 indicated, and from uncinariasis for the whole 

 season a rate of much below 1 per thousand. 

 Uncinariasis has thus become a minor and 

 insignificant cause of loss, ranking not 

 nigher than fourth, a result which must be 

 due solely to the thinning out of the herd, for 

 no artificial measures against Uncinaria have 

 been applied. The worm could not be found 

 on Polovina, Gorbatch and the Northeast 

 Point rookeries, all formerly well infested. 

 The old rookery strongholds for this disease 

 in the sands of Zapadni, Eeef and especially 

 Tolstoi, are alone now occupied and they 

 yielded only 17 uncinariated pups, 5 of which 

 were associated with starvation, out of a total 

 of 175 examined. By making these sandy 



