218 
BULLETIN OF THE BUREAU OF FISHERIES 
were mounted. On the label of each slide were recorded the field number, laboratory 
number, date and locabty of collection, species, sex, maturity, length, weight, and 
gear. The scales were studied by means of the projection apparatus described by 
Van Oosten (1923). The magnifications used were Xl9 for scales of the Clear 
Lake ciscoes and X40.5 for scales of all other fish. 
MISCELLANEOUS CONSIDERATIONS 
It is the policy' throughout this paper to apply toward the solution of each par- 
ticular question all suitable data available. As a result of this procedure there appear 
certain discrepancies in the number of specimens listed in the tables pertaining to 
different phases of the general problem of the life history of the cisco. Since dis- 
crepancies of this sort, if unexplained, may prove a considerable annoyance to a 
reader, attention will be called to the causes for at least the most important of them. 
Table 2 lists the fish upon which determinations of age were made. These 
specimens, with the exception of the 1932 Muskellunge Lake collections, separated 
into age groups and year classes, appear in the growth tables 3 to 7. The tables of 
general growth in length (10 to 14) are based on fewer specimens than tables 3 to 7 
since certain indicated age groups were eliminated because of selection by gear. 
(The 17 0-group Trout Lake ciscoes were also omitted in the computation of the 
general growth curve.) The tables for growth in weight (15 to 18) are based on fewer 
specimens than those for growth in length since part of the preserved fish used in the 
growth study were not weighed before preservation. Of course, the study of the 
length-weight relationship and of condition was based only on specimens weighed in 
the field. 
In the listing of catch per unit effort of gill nets (section on the relationship 
between density of population and rate of growth) it v/as, of course, valid to include 
fish that had not been aged. Similarly in the determination of the average length of 
all fish taken in a particular size of gill net (section on selective action of gill nets) it 
was also valid to include unaged fish. Further, the grand average length used for 
comparing the average length of an age group as determined from the combined 
catch of several different sizes of mesh with the average lengths of the same age 
group as based on the catch of individual sizes of mesh may include certain fish for 
which net records were not available. (Net records were lacking for a large part of 
the preserved fish.) The data of tables 40 and 73 are based in part on catches of 
Muskellunge Lake ciscoes taken in 1932 for morphometric investigations and included 
only incidentally in this study. None of the 1928 data is included in the analysis of 
net catches. 
The 1928 data also lacked records of sex and maturity and hence could not be 
included in the sections on sex ratio and age at maturity. 
Although some of these discrepancies are mentioned in the general discussions, a 
general statement of their origins was considered advisable. 
THE SCALE METHOD 
ASSESSMENT OF AGE AND CALCULATION OF GROWTH 
The treatment here of the growth data of the cisco is based upon the use of the 
scale method. Van Oosten (1929) established the validity of the method for this 
species in his study of the life history of the Lake Huron herring. It is assumed that 
