FLUCTUATIONS IN THE SUPPLY OF HERRING 
19 
utilize it in prospecting for herring schools, running to distant grounds, or tanning 
their seines. Most of the restrictions on gear have been made more with the idea 
of safeguarding against possible abuses than as restrictions. 
CHANGES IN THE UNIT OF FISHING EFFORT 
CHANGES IN THE PURSE SEINE VESSELS 
Of more importance in the study of abundance perhaps than the change in the 
fishing season has been the change in the unit of fishing effort. Thus the plant at 
Killisnoo employed, from 1882 to 1923, a Norwegian method of seining from oar- 
propelled seine boats (Rounsefell, 1930, p. 230). (See fig. 1.) Besides this method, 
beach seines were also used for a time by other operators. Soon after 1900 the first 
purse seines were employed for herring and so rapidly gained in favor that by 1927 
the last Norwegian type of seine had disappeared. 
No other methods of fishing have been of any importance in southeastern Alaska. 
The Kill isnoo plant twice attempted to use traps but neither attempt was successful 
and their use is now prohibited. Gill nets are used, but chiefly by the salmon trailers 
as a means of obtaining very small quantities of bait. 
As the purse seine has supplanted all other types of gear and has caught the 
bulk of the herring for many years, a study has been made of its changes in efficiency. 
This has been accomplished through a study of the purse-seine fleet rather than of 
the seine, which although it has changed somewhat in size, has not changed in shape 
or in method of use. 
The purse-seine fleet has undergone a great change since 1922, which year 
marked the start of a tremendous expansion of the summer herring fishery. Since 
then there have been radical changes in the size and age of the vessels, the type of 
hulls, the horsepower relative to the size of the vessel, the type of engines, the increased 
use of the power seine roller, and in many less important features, all of which have 
added very materially to the effectiveness of the vessel as a fishing unit. In short, 
the unit of fishing effort — the purse-seine vessel — has changed so materially in the 
short space of eight years that comparisons between catches of earlier and later 
vessels are not valid without a knowledge of the effect of these changes. 
Figure 3 shows the net tonnages of purse-seine vessels that have appeared in 
the fleet at some time from 1919 to 1929 plotted against the year in which they were 
built. It is apparent that there were two distinct periods marked by special activity 
in the building of these boats. The first, from 1917 to 1920, was undoubtedly due 
to the prosperity attending the World War. The second, from 1925 to 1928, was 
due to the phenomenal growth of the fish oil and meal industry. This second period 
of building is characterized by the adoption of the Diesel engine, which bums a very 
cheap semirefined oil, permitting the boats to make long trips at low cost and with 
less actual bulk of fuel than is the case with engines burning gasoline or distillate. 
The vessels built at the beginning of the second period, in 1925, averaged 29.2 
net tons as against 27.9 net tons in 1920, a slight increase. From then on the size 
increased rapidly, reaching an average of 41.3 net tons in 1928. The years 1927 and 
1928 were poor seasons for the herring companies, resulting in the building of only 
three new boats in 1929. The two for which we have the tonnages average 36.5. 
Although this represents a decrease in size from 1928, the number is too small to give 
a significant average. 
The size of the vessels of the fleet each year since 1923 is shown graphically in 
Figure 4, in which the boats are divided into four categories. Boats under 25 net 
