118 ALASKA FISHERIES AND FUR INDUSTRIES IN 1918. 
The percentage of increase in the number of pups ona given rookery 
is dependent upon the choosing of a landing place by the cows: 
Accordingly great variations in the percentage of gain on individual 
rookeries have been recorded during the past few years. Thus in 
1918 one rookery on which a count was made gained 154 per cent, 
while another lost 3 per cent. There is no adequate explanation 
available for these conditions. The gains for the entire herd, how- 
ever, seem to be following closely an autocatylitic curve, as was 
pointed out by Prof. G. H. Parker.* During the past six years the 
percentages of increase have been 12.54, 1.06, 11.02, 12.99, 9.44, and 
11.63, with an average of 9.78 since 1912. For a.rough calculation 
into the future it may be placed at 10 per cent, and taking into 
consideration the conservative errors of the census it may actually 
exceed this figure through a period of years. 
PERCENTAGE OF INCREASE OR DECREASE IN THE NUMBER OF PUPS IN 1918 From 1917. 






Percentage 
Total Total F 
Rookery. pups, pups, Cie 
1917. 1918. crease (—) 
ST. PAUL ISLAND. 
REGO VAs science meet eRe. food eR Lean. at 2. eee 2,520 2,540 + 0.79 
Weyikeetaa ge Soe Se oe 5 saree ele ia wr aje a hoi Bias oleae ata woe re ae re ere 2, 235 2,235 | cseeee tes 
Gorbatchtis 5s. fit eae Fo Ee Pte eae na sae ate 8,649 9, 486 + 9.67 
ATGISTION: sos che Cae washes te once tenhiet a reee eee 726 792 + 9.09 
fa) (eat hae teas ey fea a sy Abe i Eade cps yeu eras ei 17,442 19, 398 + 11.21 
Bivitteh ce'FSs Cg ERLE: Bess PRE a ee eee aes 5,060 6,325 + 25.00 
WGA POON aos ead oot oe see ae ee eae aloe eee ees 466 512 + 9.87 
Tolstoi: “Tihs ee ae ee See 15, 433 16, 725 + 8.37 
Zapadni......... 9, 828 11, 460 + 16.60 
Little Zapadni. 6, 863 9,089 + 32.43 
Zapadni Reef... ae Sars 358 536 + 49.72 
Rolovinae. ease. 4,918 5,343 + 8.64 
Polovina Cliffs; 2.2. sae. Stk ae Ree ote J eee ee eee ae 1,761 1, 882 + 6.87 
Little Polovina : 1, 260 1,491 + 18.33 
INTOYJ OVE. sass ciate oe tec cee oe Dee eee mc eee io naicies see cenae 2,921 3,335 + 14.17 
Viostochmnil: os ed Stet ateeecee shee eae casas ees ce scceetees 28, 249 31, 468 + 11.39 
MOtAMs iP ectectits bine astoe Searle Sect ch ewe wee Mews ssa oro eee 108, 689 122,617 + 12.81 
ST. GEORGE ISLAND. 
IN Ons.) 205 js cle aoae Ste ae Sen en oe awa cea cece Rees 6, 783 7,011 + 3.36 
Biarava Artie. tamen Soe h cee naeaice nance scitemmeaier sere. 5,642 5,440 — 3.58 
iy of¥e bal ae ee Se eee Bd del Se ee eA Od 1,050 806 — 2.32 
SLO] 2 Fae pee 5 RE RN Al tS OR kk SNES FON a tae Sania See Seo e 24 61 +154. 16 
Wasi ROOt ieee tae see See oe oe ne eee ere ae 1, 786 2,120 + 13.7 
Hast Clitts) socutes bh. hase nou saee semit te ae eter eeec ions eemCneciieoesae 4,050 4, 860 + 20.00 
POLARS. Sacha cccdeas eee eure Pe rw a nL Rad seis 2 19, 335 20, 298 + 4.98 
Total sbothyislands. cae o. seen eee ee ee ne eee 128, 024 142,915 + 11.63 

BREEDING COWS. 
By inference the number of breeding cows is the same as the. 
number of pups, 142,915. This is a very creditable increase of 
14,891, or 11.63 per cent from 1917. The increase showed very 
materially on the rookeries. Many of the avenues left for ingress 
and egress to the hauling grounds have closed up or are fast closing. 
Small outlying breeding masses of seals are being joined to larger 
masses and there is a general expansion rearward. ‘The season was 
marked by the establishment of very few new breeding sections. 

«Proceedings, National Academy of Science, vol. 4, p. 169. 
