Michigan Department of Natural Resources
Fisheries Research Report No.1854, 1977
Effects of DDT And PCB's on Survival of Lake Trout Eggs and Fry in a Hatchery and in Lake Michigan, 1973-1976
Thomas M. Stauffer
Abstract.-In the early 1950's lake trout in Lake Michigan were near extinction. Beginning in 1965, 1 to 3 million yearlings were stocked annually to reestablish the lake trout. Survival to maturity was good and significant numbers of young were expected by 1970 or 1971. However, no natural reproduction has been found, despite extensive sampling. The role of DDT and PCB's in the apparent failure of lake trout reproduction was determined. Mortality of Lake Michigan eggs and fry that were relatively high in contaminants was compared with that of Marquette Hatchery eggs and fry, that ore very low in contaminants, under normal hatchery incubation, during incubation in enclosures on the bottom of Grand Traverse Bay, and under stress of starvation or limited food in a hatchery.
In normal hatchery incubation, lake trout were reared from the green egg stage to 6 weeks after swim-up. In 1973-1974, overall mortality (80% ±
16) of Lake Michigan eggs (2. 7-5. 2 ppm DDT and 5.3-9. 9 ppm PCB's) and fry was about twice that (46% ±
14) of Marquette Hatchery eggs (not more than 0. 2 ppm DDT and 0. 3 ppm PCB's) and fry. However, in the similar 1974-1975 test, mortality (50% ±
9) of Lake Michigan eggs (2. 6-4. 0 ppm DDT and 4.8-8.3 ppm PCB's) and fry was the same as that (47% ±
9) of Marquette Hatchery eggs (0. 2 ppm DDT and 0.3 ppm PCB's) and fry. In Grand Traverse Bay, for eggs placed in enclosures when "green" there was no significant difference between percentage mortality of Lake Michigan eggs (2. 6-4.0 ppm DDT and 4.8-8.3 ppm PCB's) and fry and Marquette eggs (0. 2 ppm DDT and 0.3 ppm PCB's) and fry at the eyed stage (41% ±
19 and 62% ±
22), swim-up (average, 63% and 66%) and 3 weeks after swim-up (66% ±
14 and 78% ±
17). For eggs placed at eye-up in Grand Traverse Bay, mortality (30% ±
13) of Lake Michigan eggs at swim-up was significantly greater than that (10%±
5) of Marquette Hatchery eggs, but at 3 weeks after swim-up there was no significant difference (87% ±
20 and 92% ±
13). In starvation tests, mortality of unfed Lake Michigan fry was significantly less (65% ±
6) than that (89% ±
6) of Marquette fry after 11 weeks of starvation. Under stress of competition with similar-sized brown trout for a limited food supply for a period of 10 weeks after swim-up, mortality (53% ±
11) of Lake Michigan fry was not significantly different from that (61% ±
11) of Marquette Hatchery eggs and fry.
DDT and PCB's were not the cause of reproductive failure by lake trout in Lake Michigan. This conclusion was based primarily on the absence of greater mortality for Lake Michigan eggs and fry than for Marquette Hatchery eggs and fry when the two groups were reared in the hatchery in 1974-1975, when they were reared in Grand Traverse Bay (except for one instance), when they were starved and when they were subjected to stress of competition with brown trout for limited food. Also, for Lake Michigan eggs and fry incubated in the hatchery in 1973-1974 and 1974-1975, mortality was linearly correlated with DDT and PCB content in only one time period. Finally, in the hatchery experiments, no distress symptoms that were characteristic of DDT or PCB poisoning were observed.
Some data were not in accordance with the conclusion of little effect. First, in 1973-1974, mortality of Lake Michigan eggs and fry was significantly higher than that of Marquette Hatchery eggs and fry. However, difference in treatment of the eggs of the two groups before placement at the hatchery is suspected of causing the higher mortality (70-100%) of all lots of Lake Michigan eggs which obscured any possible effect of DDT and PCB's. Mortality from fertilization to eye-up in the 1974-1975 test in the hatchery was linearly correlated with amounts of DDT and PCB's which suggested an adverse effect of PCB's in this particular instance.