62 U. S. BUREAU OF FISHERIES 
1923 year-class, which as age-group VIII made up 45.8 percent of the 
1931 collection, to the extremely weak 1927 year-class, which as age- 
groups IIT to V contributed only 1.7 to 5.9 percent of the total collec- 
tions of 1930-32. In general, strong year-classes occurred in years 
of good growth—in the second and later years of life—and weak 
year- -classes were produced in years of poor growth. —Peculiarly 
enough, first-year growth and the strength of the year-classes 
exhibited no correlation. 
The analysis of the annual fluctuations in growth rate, and the 
strength of the year-classes of the Nebish Lake rock bass in relation 
to meterological conditions, showed good growth to be correlated 
with high temperatures in June and September, and heavy rainfall 
in June. It was suggested that annual variations in temperatures in 
June and September may produce variations in the length of the 
growing season. The correlation between June precipitation and 
growth may depend on the enrichment of the waters of this extremely 
oligotrophic lake by materials washed in during periods of heavy 
downpour. Substances added in June may be more fully ee 
for utilization than those introduced in other months. Strong year- 
classes were correlated with high temperatures and heavy precipita- 
tion in early season, with conditions in June especially significant. 
High temperatures and an enrichment of the lake by run-off water may 
produce favorable feeding conditions for small rock bass at a critical 
period of their life history. 
Comparisons of the data for the Nebish Lake rock bass with similar 
data for stocks from neighboring lakes suggest that to some extent the 
effects of meteorological conditions on different populations may be 
similar. For example, the 1923 year-class of rock bass was exception- 
ally strong in Muskellunge Lake and Trout Lake, as well as in Nebish 
Lake. Furthermore, ood growth of rock bass and high tempera- 
tures, especially in June, were correlated in Muskellunge Lake, and 
apparently in Silver Lake. On the other hand, a number of dis- 
crepancies suggested that conditions peculiar to the individual lakes 
at times may “modify or obscure the effects of the weather on growth 
rate and the strength of year-classes. There was some evidence also 
that the growth rate and the survival of young in different calendar 
years may be affected by fluctuations in the density of the population. 
Progress during 1939—A. study of the growth of the bluegill, 
Lepomis macrochirus Rafinesque, of Muskellunge Lake, has been com- 
pleted and submitted for publication by Dr. Clarence L. Schloemer, 
who has also made progress with an investigation of the life AOL 
of the wall-eyed pike, “Stizostedion vitreum vitreum (Mitchill), 
Wisconsin waters, and a paper on methods of determining the magni- 
tude of fish populations. Mr. David G,. Frey has nearly completed his 
work on problems related to the carp, Cyprinus carpio Linnaeus, in 
Wisconsin lakes, and continued a creel census on Lakes Waubesa and 
Kegonsa. Mr. Willard A. Van Engel terminated a study of the 
growth of the northern pike, Hsox ‘Jucius Linnaeus, in Wisconsin 
waters, and undertook an investigation of the black crappie, Pomozis 
sparoides (Lacépede), which will be continued for 3 or 4 additional 
seasons. Dr. Schloemer and Messrs. Frey and Van Engel are members 
of the staff of the Wisconsin Geological and Natural History Survey. 
