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FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Other things must be considered in evaluating 

 these analyses. The data are few, only 6 years in 

 one instance and 8 in the other, and the Weather 

 Bureau data on air temperature and cloudiness 

 cannot be a precise measurement of the tempera- 

 ture and the light actually affecting the fish. 

 Furthermore, the period during which the light 

 and the temperature changes are influential can 

 only be surmised, and other factors may be 

 important. For example, in Raquette Lake in 

 1938 the notably high water level was suspected 

 of being the cause of almost no lake trout being 

 caught. However, it was not certain whether this 

 affected the migrations or prevented the nets from 

 operating effectively. 



Considering that a significant relation was 

 established in one instance, and that other data 

 were inconclusive but showed a similar tendency, 

 it is probable that both light and temperature do 

 influence the spawning time of lake trout. 



Lake trout in Raquette Lake (Oliver R. Kings- 

 bury, report to the New York Conservation De- 

 partment, November 1935) spawn at about the 

 time of the lake turn-over. In the middle of the 

 1935 spawning season, temperatures taken at the 

 surface and at depths down to 56 feet revealed 

 no more than a 3° F. difference between top and 

 bottom. This seems to be more important than 

 the actual surface temperature in influencing 

 spawning, for the surface temperature on the day 

 the first eggs were taken was 58° F. in 1933, 52° F. 

 in 1934, and 50° F. in 1935. Merriman (1935) 

 reports lake trout spawning in Squam Lake, N. H., 

 when the surface temperature was 42° F. In 

 Otsego Lake in 1940 the lake trout were observed 

 spawning December 5, when the surface tempera- 

 ture was 37° F. No facilities were available for 

 taking deep-water temperatures at that time, but 

 in 1941 the fish were observed late in their spawn- 

 ing season on December 3, when the water tem- 

 perature was uniformly 43° F. from the surface 

 down to 60 feet. These wide variations in surface 

 temperature indicate its slight value as a deter- 

 minant of the date of spawning. 



Such differences in the progress of cooling in 

 different lakes are probably associated with the 

 depths of the lakes, and it appears that the depth 

 of a lake is associated with the time of lake-trout 

 spawning. Table 5 presents data from the files of 

 the New York State Conservation Department on 

 the time and duration of lake-trout spawn taking 



Table 5. — Duration of lake-trout spawn taking operations 

 by State Conservation Department in some New York 

 lakes 



' Data not available. 



 Same dates were reported (or each year. 



' Data depended on hatchery schedule rather than lake-trout migrations. 



operations in some New York lakes. Figure 2, 

 which incorporates information from table 5, from 

 Rayner (1941) for Skaneateles Lake, and from my 

 observations on Otsego Lake, shows this relation 

 graphically. 



It appears that the lake trout spawn early in 

 the shoal lakes and later in the deep lakes. If, as 

 indicated previously, they spawn at about the 

 turn-over time of the lake, this would be expected, 

 as the deeper lakes cool off more slowly. 



Like so many rules, the one that the deeper 

 the lake the later the lake trout spawn has an out- 

 standing exception. In Seneca Lake, the deepest 

 lake in New York State (625 feet maximum 

 depth), the lake trout spawn the earliest. They 

 start in late September and continue through 

 October, spawning in water from 100 to 200 feet 



