SALMON AND SALMON FISHERIES OF SWIFTSURE BANK 
737 
newer vessels have been fitted out with better engines and equipment, and in 
recent years Diesel engines have been used almost exclusively by the larger vessels. 
These engines, allowing a far greater range of operation and greater economy than 
had been possible with gasoline engines, contributed much to the efficiency of the 
larger vessels. 
The average horsepower of engines has also gradually increased. For example, 
the average power of vessels in the 10-14 net-ton class has increased from 22.4 hp. 
in 1915 to 30.9 hp. in 1934. Larger vessels show a lesser increase in the case of gasoline 
engines, but the many Diesel engines are of much greater power. The maximum 
power of the largest vessels prior to 1918 was 55 hp., whereas vessels above 45 net tons 
now average 132.5 hp. The present averages for the 7 size-classes of vessels between 
10 and 40 net tons are 36.5, 46.0, 56.6, 68.1, 88.1, 97.0, and 109.8 hp., respectively. 
The relatively greater power of the larger vessels undoubtedly adds to their efficiency. 
An important difference in earlier years existed in the size of the seine carried. In 
general, the larger seines were more efficient than the smaller ones and, since the size 
of the seine was necessarily limited by the space available for handling and stowing, 
it was generally proportional to the size of the vessel. 
Throughout the years the human factor, although difficult of measurement, has 
always been of great importance. The most successful fishermen have constantly 
built larger and better vessels, while the older, smaller craft ha ve usually been manned 
by less active men or by newcomers to the fishery. For these reasons the present 
analysis of vessel efficiency has been confined to a study of the relation of vessel size 
to size of catch. 
In order to facilitate vessel-catch comparisons, the fleets of all years from 1916 
to 1934 have been divided into size classes of 5 net tons each. The annual numbers 
of vessels in each class, for the summer and fall fleets, are given in tables 12 and 13. 
Theoretically, any difference in efficiency between vessels of varying size should 
be reflected in a proportional difference in the average size of their catches. In order 
to determine such differences and to measure their degree, the average catches, over 
a considerable period of time, of vessels of different size classes were compared. Catch 
data used were from the years 1916-19, 1922-25, and 1928-34, in order to include 
the various building periods of the vessels and the fluctuations in fleet size. The 
size class of vessels from 10 to 14 net tons was selected as the unit of relationship 
since this class was well represented throughout the period of years covered. 
Direct comparisons of annual average catches could not be used because of the 
seasonal fluctuations in abundance of the various species of salmon, with the resultant 
influence that the presence of one species might have on the size of the catch of another. 
Therefore, data for different species were used for comparison during different parts 
of the fishing season. Sockeye catches were used for determining averages for the 
summer fishery of even years, pink-salmon catches for that of odd years, and coho 
and chum catches for the fall fishery in all years. 
Data for individual species were limited to the part of the season when they 
were sufficiently abundant to warrant fishing, and when other species were less 
numerous than the one sampled. Pink-salmon catches for most years were those 
from a period between July 29 and September 15. This period was shifted one week 
earlier in 1929 and one week later in 1933 in accordance with the time of appearance 
