AGE AND GROWTH OF THE CISCO 
297 
Haakh (1929) in his study of the age and growth of several species of fisli in the 
Bodensee found that net selection led to inaccurate determinations of the average 
length of some age groups. 
Wagler (1927, 1930a, 1930b, 1932, 1934) in his investigations of the coregonids 
of Bodensee and other north alpine lakes mentioned repeatedly the distorting effect 
of the selective action of the gill nets used in taking his samples for the study of age 
and growth. The effects of the selection were noticeable particularly in the high 
average lengths determined for the younger, smaller age groups and in the great 
variation in the relative abundance of the different year classes as determined from 
the various gill nets used. Wagler held that a close relationship exists between net 
selection and maximum girth of the individual fish (cf. Lechler, 1929). Elster (1934) 
in his study of the Blaufelchen ( Coregonus wartmanni ) expressed opinions similar to 
those of Wagler. 
Van Oosten (1929b) in his discussion of the problems of the commercial fisheries 
of the Great Lakes pointed out the complex nature of the question of selectivity in 
the gill nets of the commercial fishery and included a small amount of data on the 
number and size of small trout ( Cristovomer namaycush) and several species of chubs 
(. Leucichthys spp.) taken in 2/- and 2%-inch mesh nets. 
In a later paper Van Oosten (1933) published a preliminary report of experimental 
chub net investigations conducted by the United States Bureau of Fisheries in Lake 
Michigan waters, 1930-32. The data presented included average catch per net, 
expressed in pounds and number of fish, for the lake trout and the chub in five different 
sizes of mesh. The meshes used were all of commercial fishery size, and varied from 
2% to 3 inches, stretched measure. The variation in the catch of chubs in nets of 
different size mesh was striking. In lower Lake Michigan nets of 2%-inch mesh 
caught more than twice as many chubs as did nets of 2 /(-inch mesh, and eight times 
as many as nets of 3-inch mesh. 
In view of the marked disagreement that the preceding review shows to exist among 
some authors as to the nature and scope of the selective action of gill nets, it appears 
probable that each species and each locality offers its own special problem of gear 
selection. 
The selective action of gear as size of mesh affects the amount of total catch (with 
respect both to numbers and weight) is particularly noteworthy. The existence of an 
intensive commercial fishery employing a more or less standard size mesh can, how- 
ever, exaggerate the differences of catch between two different sizes of mesh. Ordi- 
narily all the commercial gear of the same type used in a region for the capture of a 
species or group of species of similar size will meet approximately the same specifica- 
tions particularly with reference to the size of mesh. Consequently there tends to be 
a great reduction in numbers in that portion of the population most liable to capture 
by the standard commercial gear. The withdrawal of large quantities of commercial 
size fish produces an abnormal condition in size distribution of the population as a 
whole. The introduction of nets of other, noncommercial sizes of mesh may then 
lead to comparisons that do not describe accurately the fishing action of the nets in 
question. Data based on catches from a population unaffected by commercial 
fishing might be expected to show somewhat less sharp selectivity than those from a 
population subjected to heavy fishing. It will be seen that the data of the present 
investigation tend to support this view. 
