32 U. S. BUREAU OF FISHERIES 
Great Lakes waters. Continued study has supported this earlier sug- 
gestion. In a series of comparisons, no significant differences could 
be found between abundance curves prepared from data that ignored 
the time element and curves prepared from data that included con- 
sideration of fishing time. The knowledge that the consideration of 
fishing time need not enter in the computation of fluctuations in 
abundance has made possible a great simplification of statistical 
procedure. 
Methods have been developed whereby fluctuations in the abund- 
ance and production of fish and in the intensity of the fishery may 
be expressed in terms of simple index numbers. These indexes of 
abundance, production, and fishing intensity are all computed with 
reference to average conditions over the 6-year period, 1929-34. <A 
convenient feature of the method lies in the fact that the basic data 
for the different statistical districts can be combined readily by a 
simple process of summation. 
Statistical data on the fluctuations in abundance and production 
of the yellow pike-perch have proved of great value in connection 
with problems concerning the effectiveness of artificial propagation 
of the species. For the past several years yellow pike-perch have 
been exceptionally plentiful in Saginaw Bay, the chief production 
center of the species in Michigan waters. Many fishermen believe 
this increase in abundance to be the result of the intensive artificial 
propagation that was begun in 1924. However, the fluctuations in 
abundance and production of yellow pike-perch in Saginaw Bay 
over the period 1929-85 showed no correlation with the variations in 
the numbers of fry planted in earlier years. Statistical data for 
other areas revealed that the abundance of pike-perch increased 
simultaneously throughout the State of Michigan waters of Lake 
Huron and Lake Michigan. Although no fry were planted in 
southern Lake Huron, southern Lake Michigan, nor Green Bay, the 
relative increase in the abundance of yellow pike-perch was as great 
in each of these areas as in Saginaw Bay. A report of this study 
appears in the 1986 Transactions of the American Fisheries Society. 
PIKE-PERCHES OF LAKE ERIE 
A manuscript entitled, “Morphometric and Life History Studies of 
the Pike-Perches (Stizostedion) of Lake Erie,’ was completed by 
Dr. H. J. Deason during 1936. Most of the conclusions of these 
studies have been presented in Progress in Biological Inquiries for 
1933, 1934, and 1935. There are, however, two additional major 
conclusions, not previously reported. In order to determine the rela- 
tion between age and growth rate and various characters and body 
proportions of the blue and yellow pike-perches, ages were deter- 
mined from the scales of specimens employed for the taxonomic 
study. Within a single population the morphometric characters 
varied according to age and growth rate. The differences in age or 
rate of growth between the yellow and the blue pike-perch of Lake 
Erie, however, could be only partially responsible for the observed 
differences in the average values of certain morphometric characters. 
Because of the fact. that the ranges of variation of the characters of 
the blue and yellow pike-perch overlap to a considerable extent, that 
the habitats are not mutually exclusive, and that individuals inter- 
