Page 843 - The Toxicology of Fishes
P. 843

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
   838   839   840   841   842   843   844   845   846   847   848