LAKE TROUT BREEDING HABITS 



71 



A check of the natural spawning of lake trout 

 in Otsego Lake provided further evidence that 

 natural reproduction is efficient. On December 28, 

 1941, about 25 days after the trout were observed 

 on the spawning area, a sample of 309 eggs was 

 collected from under the rocks along shore with 

 a small rubber bulb and tube. Of these 309 eggs, 

 18, or 5.8 percent, were not fertihzed, and 47, 

 or 15.2 percent, had died. Seventy-nine percent 

 of the eggs were ahve and apparently entirely 

 normal after having been on the lake bottom nearly 

 a month. This probably represents a near mini- 

 mum figure for the survival (exclusive of those 

 eaten by predators) inasmuch as the eggs were of 

 necessity collected in only a few inches of water 

 where they were subject to heavy wave action. 

 The vast majority of the eggs were laid in deeper 

 water out of reach of available collecting appara- 

 tus and where they should have been better 

 protected. 



TEMPERATURE REQUIREMENTS 



Lake-trout eggs appear both to require and to 

 withstand slightly lower temperatures than the 

 eggs of other trout. Embody (1934) found that 

 brook- and rainbow-trout eggs suffered excessive 

 mortaUty and developed at a different rate when 

 the water temperature was below 37.4° F.' He 

 found, also, that lake- and brown-trout eggs 

 followed the same rate of development down to 

 35.2° F., and he judged that development pro- 

 ceeded normally. Brook trout usually spawn in 

 spring water so that their eggs are not subjected 

 to near-freezing temperatures during the winter 

 (Greeley 1932, Hazzard 1932, White 1930). Rain- 

 bow trout normally spawn in the spring when the 

 water is warming (Rayner 1941). Cook (1929) 

 reports that lake-trout eggs develop satisfactorily 

 at the Duluth, Minn., hatchery where water 

 temperatures remain about 32.5° F. throughout 

 the winter. The 140-day incubation period of 

 lake-trout eggs in Otsego Lake indicates an 

 average temperature of 36° or 37° F. in the egg- 

 development tables of Embody (1934). At the 

 Rome, N. Y., State hatchery high mortality 

 occurred in lake-trout eggs developing at water 

 temperatures above 50° F. when other trout eggs 

 developed normally. In other hatcheries, lake- 

 trout eggs from the same source developed nor- 



* Rainbow-trout cpgs suiterod hiph mortality at temp(?raturcs below 43° F., 

 but Emtwdy thought that in some cases this was due to inferior eRjts. 



mally at lower temperatures. These facts would 

 indicate that lake-trout eggs can develop success- 

 fully in a lake in the winter, so long as they do not 

 freeze, and that they do not require spring water. 

 No data arc available on the temperature 

 requirements of the alevins. In the spring of 

 1941 they left the spawning area in Otsego Lake 

 when the water temperature was about 55° F. 

 It seems likely, therefore, that they avoid tem- 

 peratures above 60° F. 



EFFECTS OF PREDATION 



The data on the survival of eggs in Otsego 

 Lake do not indicate the true value because 

 they do not consider the removal of eggs by 

 predators. Predators are an ever present danger 

 to lake trout from the egg stage almost to maturity, 

 and cause a loss which is exceedingly difficult 

 to evaluate. No precise measurements have 

 ever been made on the effects of predation at any 

 stage in the growth of wild trout. 



Many are the potential predators of eggs and 

 alevins. Table 6 lists the animals captured 

 within 100 yards of the lake-trout spawning area 

 in Otsego Lake during April and May 1941. 

 Many of these would destroy eggs if eggs were 

 availabe to them. Atkinson (1931) and Greene, 

 Hunter, and Senning (1932) found that numbers 

 of lake-trout eggs were eaten by suckers {Cat- 

 ostomus commersonii) and bullheads {Ameiurus 

 nebulosus). Both of these species occur in Otsego 

 Lake although they were not captured in the 

 immediate vicinity of the lake-trout spawning 

 area. Greeley (1936) states that a fisherman 

 reported finding lake-trout eggs in the stomachs 

 of Otsego Lake whitefish. Rayner (1941) found 

 many lake-trout eggs in the stomachs of adult 

 lake trout. A female taken by the writer on the 

 Otsego Lake spawning area had 13 lake-trout 

 eggs in its stomach. Small lake trout may be 

 even more voracious predators. W. C. Senning, 

 in a letter to me, reported finding lake-trout eggs in 

 every one of 31 small lake trout taken on the 

 spawning grounds in Seneca Lake in the fall of 

 1942. These lake trout ranged from 6K to 13 

 inches in length, and one 12-inch individual 

 had eaten 147 eggs. White (1930) found large 

 numbers of brook-trout eggs in brook-trout stom- 

 achs. Metzelaar (1929) reported that rainbow 

 trout ate numbers of their own eggs. Greeley 

 (1932) found brooks, browns, and rainbows to 



