PROGRESS IN BIOLOGICAL INQUIRIES, 1938 19 
611,000,000 pounds annually, of which 487,000,000 pounds consisted 
of the various species of groundfish. Fluctuations in the abundance 
of haddock, which comprised about 45 percent of the catch during 
the above period, have been determined as part of a biological study 
of the species, but no information has been available concerning the 
other species—cod, pollock, hake, cusk, wolffish, whiting, halibut, 
rosefish, and the various flounders. During recent years the industry 
has been developing markets for all species, bringing about a marked 
change from former years when boats sought only haddock, and 
took other species but incidentally. This means that the total catch 
of any one species is now partially dependent on the abundance and 
market value of the others. 
Various other factors must be considered in an analysis of ground- 
fish abundance. For example, in a fishery that draws upon several 
species, the relative abundance of any one species is not necessarily 
indicated by the average catch of that species per unit of fishing 
effort. The average catch must be qualified by such information as 
the depths and grounds fished and the quantities of other species 
caught, so that it is clear whether the fishing effort was directed to- 
ward the catching of the species in question, or whether the average 
cited is merely of catches made incidental to the pursuit of another 
species. For example, the vessels seeking rosefish trawl exclusively 
in the deeper waters, around 70 to 100 fathoms. Only an occasional 
rosefish is taken in shallow water, and these fish are not caught in 
commercial quantities at medium depths. Therefore, a low catch of 
rosefish per unit of effort in shallow-water zones would not indicate 
a low abundance of rosefish in general. As another example, al- 
though the gray sole is taken to some extent at lesser depths, the 
bulk comes from certain types of bottom in the deeper water. The 
lemon sole, on the other hand, is abundant only in shallower areas. 
These differences in habitat have raised several problems of analysis, 
the solution of which is treated more fully below. 
Another major problem is the study of the changes in the fishing 
fleet in respect both to numbers and to size and type of vessel, in 
order to gain a measure of the total fishing effort expended. For a 
great many years nearly all of the groundfish were taken with hook- 
and-line, but in the last 20 years there has grown up a huge and 
expanding otter-trawl fleet. At the same time, the number of line 
trawlers has gradually decreased until they are now a minor factor 
in the fishery. Changes in the vessels affect not only their efficiency 
in respect to their chosen type of gear but also their adaptability to 
other gears. Many vessels are so constructed that it is possible to 
shift to whatever gear is producing the greatest monetary reward at the 
moment. This adaptability means that there exists a great potential 
capacity to take any particular species. Although this capacity is 
seldom exercised to any great extent, owing to an economic balance, 
the ability to shift fishing effort from one species or fishing bank to 
another must be realized and fully considered before judging the 
effect upon any species of changes in the abundance of another. 
The total catch during this period of expansion has remained at a 
high level, owing principally to two developments in addition to the 
increase in number and efficiency of the fishing vessels. One impor- 
tant factor in maintaining the poundage has been the shift to other 
species, such as the rosefish. From 1930-35, this species contributed 
