Page 843 - The Toxicology of Fishes

Reproductive Impairment of Great Lakes Lake Trout by Dioxin-Like Chemicals 823

8000
Great Lakes Lake Trout
Commercial Harvest 1885–2000

6000 Lake Michigan
Lake Ontario
Commercial Catch 4000 Lake Huron
Lake Superior

2000

0
1880 1900 1920 1940 1960 1980 2000 2020
FIGURE 21.2 Great Lakes lake trout populations over the 20th century based on commercial catch per unit effort (CPUE).
(Data are from Baldwin, N.A. et al., Commercial Fish Production in the Great Lakes 1867–2000, Great Lake Fisheries
Commission, Ann Arbor, MI, 2004; http://www.glfc.org/databases/commercial/commerc.php.)

The lake trout once had self-sustaining populations in all of the Great Lakes (Figure 21.2); however,
populations of adult lake trout were extirpated from the Great Lakes by the middle of the 1950s, except
for the stocks in Lake Superior. Overharvesting by commercial fishermen and the accidental introduction
of the sea lamprey in to the Great Lakes through the Erie Canal have been classically blamed for the
demise of the populations of lake trout in the Great Lakes. Sea lampreys entered the Great Lakes in the
early 1900s and have a certain proclivity for the lake trout. Sea lamprey populations grew in the Great
Lakes and were considered abundant in Lakes Ontario, Erie, Huron, and Michigan by the mid-1940s
(Eshenroder and Amatangelo, 2002).
Reestablishment of lake trout populations in the Great Lakes has been a major effort of the resource
managers in this region. Stocking programs for the lake trout have been maintained by the U.S. Fish
and Wildlife Service for the past 40 years. These programs have resulted in lake trout juveniles (100,000
annually) and fry (1.25 million annually) in the U.S. and Canadian waters of the Great Lakes (Hansen,
1999). The other major program that was initiated by resource managers around the Great Lakes to
protect and restore lake trout populations was a sea lamprey control program that focused on the use of
chemical control agents (specifically toxic to the larval stages of the sea lamprey) and the use of physical
and electric barriers to stop the migration of adult sea lamprey up rivers to their spawning areas (Jude
et al., 1981; Marsden et al., 1988). The lampricide that had the greatest use was 3-trifluoromethyl-4-
nitrophenol (TFM), which was sprayed in the shallow, backwater, spawning grounds of rivers known
to have sea lamprey spawning runs. TFM is toxic to the larval (amneocete) stage after the sea lamprey
emerges from the bottom sediments, while resident fish are not affected (Applegate et al., 1961). Other
rivers were fitted with mechanical weirs capable of stopping the adult sea lamprey from migrating
upstream to spawn. Both of these programs continue in the Great Lakes today. These extensive programs
have been largely successful in reestablishing adult populations of lake trout in all of the Great Lakes
where they had previously thrived.
Although populations of lake trout were reestablished, there was little or no evidence of natural
reproduction in certain lakes of the Great Lakes. The years of stocking fish, control of lamprey popu-
lations, and ban on commercial fishing were successful in the restoration of adult populations of lake
trout; however, even with ample numbers of lake trout of spawning age that produced viable gametes,
signs of natural reproduction in this species in the lower Great Lakes are meager. No signs of natural
reproduction have been observed in Lake Michigan since the stocking programs began over 40 years