346 U. S. BUREAU OF FISHERIES 
MORTALITY OF SEALS AT SEA 
There are some indications that mortality rates of seals at sea should 
be increased, The rates naturally fluctuate considerably from year to 
year. For several years there has not been as large an increase in the 
number of killable seals as was to be expected on the basis of using 
the present mortality rates. If this continues it will be an indication 
that with the growth of the herd natural enemies, diseases, or unfavor- 
able conditions at sea increase faster than the seals increase, and larger 
mortality rates will be necessary. 
COMPLETE COMPUTATION 
The following summary shows the number of the various classes of 
animals in the Pribilof Islands herd in 1936. ‘The methods used to 
compute the number of animals in each class are also shown. The 
total number of seals of all classes is estimated to be 1,689,743. This 
is an increase of 8.95 percent over the preceding year. The larger 
percentage increase than in former recent years is due to the smaller 
take of 3-year-old males, which naturally leaves a greater percentage 
of living animals of this class. The estimate, of course, is based on the 
assumption that the usual percentage of 3-year-olds survived but did 
not return to the islands. 
Complete computation of fur seals, Pribilof Islands, as of Aug. 10, 1936 
















St.Paul | St. George 
Class Island Island Total 
PUPS EStimatedeeses_ Aeevys <2 PU AAT AT “eee Fh, oe airy ae ee 9 2 429, 767 97, 081 526, 848 
Breeding cows, 3-years old and over, by inference__________-________- 429, 767 97, O81 526, 848 
HaremEbulls counted lets Lae eS ee en 10, 055 2, 266 12, 321 
Tdletbulls= counted Ses a ed es ee ee 2, 253 480 2, 733 
Yearlings, male and female, estimated 
Hemalesyborn tts 5ha< 2 ed * eR a Le ee ee 198, 996 44, 945 243, 941 
INatinral mortality. 40iperGeni ae a= ee a ae an oe een en 79, 598 17, 978 97, 576 
Weanlinayfemales; Anise On 1O36 2 2aee oe a age eee 119, 398 26, 967 146, 365 
SNE VCEISVT O10) gic gd hallo B49 peter pene a raat haan mea cull yur oe el 198, 997 44,945 243, 942 
Naturalimortality.,40ipercent!-- = 25s ss smens ee eee 79, 599 17, 978 97, 577 
Yiearlingwmaless Aue. 10) NOS6sacen- eee ee ee eee nee. 119, 398 26, 967 146, 365 
2-year-olds, male and female, estimated: 
Wearlinesfemaless Auigs 10198) ee eae 5 eee Ee 110, 556 24, 970 135, 526 
INaturalimortality; Voipercemtisese: =— 9 es eee ene 16, 583 3, 746 20, 329 
2-year-old females; Aire. 10193 6ss-5 en ee ee 93, 973 21, 224 115, 197 
Viearlinsymaless Aue sOv1935e2222 "2. See. 2 See tS 110, 555 24, 970 135, 525 
INaturalimortalityali-pypercenta=.- esa + eae eee 19, 347 4, 370 23, 717 
2-Vear-Olaenalesipeeinmineel O36a ss. an aes 8 2. eee nee ee 91, 208 20, 600 111, 808 
2-year-oldnalesikilledsin! 1936-65-20. - see ee eee eet 923 380 1, 303 
2-vear-oldwmales Atos 1 Om1G36 lene. pe eee oe 90, 285 20, 220 110, 505 
3-year-old males, estimated: 
2-year-old males, tAnio~ 10; 31935528 8 a eee ee eee Sea 83, 575 18, 980 102, 555 
Naturallmortality,.12-5 percent=s=--o-s2e— = 2 eee = Se 10, 447 2, 372 12, 819 
3=V.ear-old malessbeeinming 193 60 eee ee eee ee oe Cee 73, 128 16, 608 89, 736 
3-Vear-old males tilled! ini 936 ha eee ee 41, 394 8, 172 49, 566 
3-Veal-Oldwn ales PAuIpe el 0 e193 haan: eee eee eee eee 31, 734 8, 436 40, 170 





