PROGRESS IN BIOLOGICAL INQUIRIES, 1936 9 
erously provided space and facilities for the work. The cooperation 
of the Woods Hole Oceanographic Institution is gratefully acknowl- 
edged, especially the assignment of the research vessel Atlantis for 
haddock trawling cruises, and the personal advice and interest of 
Prof. Henry B. Bigelow. The assistance and cooperation of fisher- 
men and fish dealers in permitting the use of their records and in 
other ways is also acknowledged with pleasure. 
HADDOCK 
The great New England otter-trawl fishery, a development of the 
past two decades, has depended to a large extent on the extensive 
haddock populations found on Georges and the Nova Scotian Banks. 
The increasing catch of haddock roughly paralleled the increase in 
the number of boats until 1929, when the total catch began to decline 
despite the increased fishing effort. In the fall of 1930 the Bureau 
inaugurated an investigation of the haddock fishery to determine the 
basic causes for the declining catch. The program of investigation 
was designed to obtain an accurate measure of the extent and cause 
of changes in the abundance of haddock and to develop a practical 
plan of management that would maintain the fishery at maximum 
productiveness. 
Owing to the extent and variability of the fishery, the objectives 
required the establishment of a long-period program of observation 
and study. This program has produced results that are encouraging 
although progress has been slow because of limited personnel and 
facilities for work at sea. It has now been shown that the haddock 
populations on the New England and Nova Scotian Banks are sub- 
ject to wide fluctuations in abundance not only from year to year, 
but to an even greater extent over periods of years. Since 1922 the 
greatest increase in abundance in successive years (as shown by 
average catch per unit of fishing effort) was about 40 percent, while 
the greatest decrease was between 40 and 50 percent. However, 
over a period of years the range of variation has been much greater, 
with increases running as high as 220 percent and decreases to the 
extent of 80 percent. Furthermore, analysis shows that since 1914 
there have been two long-period cycles in haddock abundance on 
Georges Bank and adjacent areas. Minima in the abundance curve 
occurred during 1914-16, 1928, and 1930-31; while maxima appeared 
during 1918-19 and 1927. Since 1931, there has been a third upswing 
which by 1936 had increased the apparent abundance of marketable 
fish to nearly twice the 1931 minimum. Even with this increase, 
however, the present peak still is little more than one-third as high 
as the previous peak in 1927. 
The direct cause of both long- and short-period fluctuations in 
abundance appears to be the success of year-class survival; i. e., the 
number of young of any single brood which reach commercial size 
during any year or period of years. It has been demonstrated that 
since 1923, when the records first began listing scrod haddock (114- 
to 214-pound fish) separately, increases in the level of abundance 
invariably have been accompanied or immediately preceded by in- 
creases in the catch of scrod; while decreases in the level of abun- 
dance have been accompanied or preceded by decreases in the scrod 
