almost 100% Pacific herring. Only one early fetus of the Pribi- 

 lof fur seal had previously been known. Kenyon's trip brought 

 to light 31, some of which were later used in describing fetal 

 pelage and dentition. 



A positive correlation between size of fetus and size and age 

 of mother was clearly indicated. Pelagic collections since 1950 

 have repeatedly confirmed this relationship. So far as we 

 know, however, no one has studied the relationship between 

 size of the newborn and size and age of the mother. 



Kenyon documented, perhaps as fully as it will ever be, the 

 Tlingit methods of sealing (Kenyon 1955). An Indian fisher- 

 man told him that "in shallow water, about 30 fathoms [55 

 m], a fur seal will swim along a line and rip strips of skin from 

 hooked fish" (Kenyon 1952:246). 



The next winter, Wilke went to Crawfish Inlet and examined 

 107 seals taken by natives between 16 and 27 January 1951. 

 Again all were adult females and again the stomach contents 

 were over 99% Pacific herring (Wilke and Kenyon 1952). 

 Wilke collected here the first series of adult skulls for taxo- 

 nomic comparison with those of Asian seals (Wilke 1951:12). 

 After the 1951 Sitka expedition, no further attempt was made 

 to exploit aboriginal sealing for research purposes. The inter- 

 national pelagic research programs launched in 1952 provided 

 a better way to obtain information. 



The summer of 1950 on the Pribilofs was a busy one. Ken- 

 yon and others made a full-scale test on all rookeries of the 

 "reconnaissance" method of estimating pup populations. 

 During the last 14 d of July, living pups were estimated on 

 both islands. (For St. George Island, this was the first pup 

 count since 1924.) Dead pups were counted individually on 

 most of the rookeries and were estimated by reconnaissance on 

 the others. The reconnaissance technique was tried again in 

 1951 and never thereafter on a large scale. The results obtained 

 in 1950-51 seem to have been well within the limits of possi- 

 bility, however, and the technique should perhaps be re- 

 studied. 



The 1951 totals were (Kenyon et al. 1954:29, with corrected 

 arithmetic): 



St. Paul Island 



Living Dead All Percentage 

 pups pups pups dead 



280,400 76,300 356,700 21.4 



Extrapolated to the Pribilof Islands on the basis that the St. 

 Paul harem bull count is 0.829 of the Pribilof count, the num- 

 ber of pups born in 1951 was about 440,000. 



The highest pup mortality, 39%, ever estimated for a rook- 

 ery was on Polovina in late August 1950 (Kenyon et al. 1954, 

 table 12, p. 31). 



In 1950 the returns from the first all-out tagging program 

 were studied. In 1947, 19,183 pups of both sexes had been 

 marked with A-series tags. In 1950 there were recovered 1,264 

 A-tagged 3-yr-oId males, representing 13% of those tagged 

 (Kenyon et al. 1954:71). The first estimate, by the Petersen- 

 index method, of a fur seal year class indicated that 530,000 

 pups were born on the Pribilofs in 1947 (Kenyon et al. 

 1954:22). 



It was also the first estimate based on tooth-ridge counts, 

 rather than body length, as an index of age. Daily throughout 

 the killing season on St. Paul Island 20 right upper canine teeth 

 were analyzed. 



A crude hut (blind) was erected above Kitovi Amphitheater 

 on the site of the present concrete structure, and photographs 

 of the rookery were taken at 5- or 10-d intervals from 15 May 

 to 27 September 1950. The results were useful in 1952 to 

 George A. Bartholomew when he studied the Kitovi Amphi- 

 theater harems in detail (Bartholomew and Hoel 1953). The re- 

 sults also showed that all harem bulls were on station by early 

 July. This in turn led, in 1951, to an advance of 5 din the start- 

 ing date of the annual bull count (Thompson 1954:61). By 

 starting on 10 rather than 15 July, the counting crew now has 

 more leeway before the late July breakup of harems. 



In 1950, 100 fur seal hearts and 100 salted, dried diaphragms 

 were sent to the Bureau of Animal Industry Laboratory at 

 Beltsville, Md., to be examined for filariid worms and trichinid 

 worms. None was found. 



The testes of about 150 seals, ages 3, 4, and 5, and those of 

 about 20 bulls were preserved in Bouin's solution and sent to 

 Richard G. Blandau, of the University of Washington School 

 of Medicine, in 1950 and 1951. His findings were summarized 

 by Kenyon et al. (1954:49-50). Evidently sperm formation may 

 begin in a few precocious 3-yr-olds but is not routine until the 

 fifth year. All healthy bulls, whether "idle" or "harem" are 

 evidently producing sperm throughout the summer. No study 

 of male fecundity has subsequently been made. 



During the killing season of 1950, Kenyon weighed the testes 

 of 222 tagged 3-yr-olds. 14 He reasoned that, because older 

 males arrive on land in summer ahead of younger ones, the 

 sexually more mature members within an age class may arrive 

 ahead of the sexually less mature ones. He found, however, no 

 important difference in testes weights of earlier arriving and 

 later arriving males, as follows: 





Number of 



Mean and range of 



Date killed 



seals 



weights (g) 



17-28 June 



90 



27.93 (9-74) 



22-26 July 



132 



27.03 (10-78) 



The 3-yr-olds were screened for size by the killing crew. If a 

 random sample of 3-yr-olds had been taken it might have 

 shown the effect that Kenyon postulated. 



The bacula of a few known-age seals collected in 1950 were 

 sectioned and stained by a technician at Providence Hospital, 

 Seattle. The slides did not show evidence, as had been hoped, 

 of annual growth layers. 



Kenyon and Scheffer identified the sex of 1 ,000 seal pups on 

 St. George Island on 4 August 1950 and found 505 males to 

 495 females. (Ten years later, Niggol (1960) reported that the 

 ratio in 6,729 fetuses and pups was 51.7% males.) 



On 3 October 1950, Kenyon supervised the killing of 100 

 female seals on Northeast Point Rookery. He sent the genital 

 tracts to Oliver P. Pearson and Anita K. Pearson. The Pear- 

 sons had worked with Enders and were now continuing their 

 studies of mammalian reproduction at the University of Cali- 

 fornia. The Pearsons' report ( 1 950) ' 5 confirmed the fact of 

 delayed implantation in the fur seal. 



"Kenyon, K. W. 1950. Analysis of tagged 3-year-old fur seal tested samples. 

 1950 kill. Unpubl. manuscr., 2 p. Northwest and Alaska Fish. Cent., Natl. Mar. 

 Mammal Lab.. Natl. Mar. Fish. Serv., NOAA, 7600 Sand Point Way NE., 

 Seattle, WA 98115. 



"Pearson, A. K., and O. P. Pearson. 1950. Delayed implantation in the 

 northern fur seal. Unpubl. manuscr. Northwest and Alaska Fish. Cent., Natl. 



36 



