Lake Michigan surface area is 22,400 square miles and its main depth is 276 ft. Its fauna is generally typical of North American oligotrophic lakes. The original fish populations included 10 coregonines and one salmonine. The lake whitefish, the lake herring, and the lake trout were most abundant.Man's activities have caused great changes in the lake in the past 120 years. Although changes in water chemistry and in the lower biota have been generally modest (except locally), those in salmonid communities have been vast. Exploitation, exotic fish species (especially the sea lamprey and alewife), and accelerated eutrophication and other pollution, all have played a role in bringing about the modifications (mostly marked declines in abundance) in salmonid communities.Commercial exploitation was largely responsible for the changes in the salmonid communities before the invasion of the lamprey (1936), although eutrophication and other pollution, and alterations of spawning streams, also were important. The lamprey and alewife (first reported in 1949), however, have exerted a greater impact than the other factors in recent decades.
Alternating-current el.ectromechanical devices instal.led in the mouths of streams have proved effective in stopping the spawning migrations of ,the parasitic sea lamprey (Petromyzon marinus) which has seriously damaged Great Lakes fisheries. In a few streams, excessive mortality has •occurred to other fish at the Xlternating-currem barriers. A direct-current unit was developed in an attorapt to reduce .this mortality. This direct-current "diversion device" consists .o•f a row of suspended negative electrodes which begins at 'the end <)•f a trap wing and extends across the river at a downs.tream angle of 45 ø and a series of p?pes (positive electrodes) driven in, to the s•tream bank. A second array, consisting of horizontal pipes installed downs.tream and parallel to the suspended electrodes and connocted ,to a series of rods driven into the bank near the posRi.ve electrodes, controls {he electrical field and dissipates the collecting influen•ce of 'the positive side of •he circuit. The electrical fiel. d is esd:ablished from the end .of 'the trap wing to the opposite 'bank. Fish are diverted away •from the negative eleCtrodes and toward •he bank near which 4•he trap is located. The array is activiated by pulsated direct current of essentially square wave shape with pulses at a duty cycle ,of 0.66 and a repeti'tion rate of 3 per second. Direct-current diversion devices were ,operated in conjuncti.on wi.th alternafir•g-currer•t barriers during 1956 4n fhe {]l•ocolay River, Marquette County, and the Silver River, Baraga (3oumy, Michigan. A .tota.1 of 15,814 fish .cc•m•prising 21 species was handled at the Chocolay River with a mortali•cy cff 930, or 5.9 perrein. If mor•li•fies of fish moving downstream are disregarded, only 287, or 1.9 percent, of the fish moving upstream were killed in the Clxocolay River. In the Sfiver River, 78,648 fish comprising 21 species were taken [rom qhe trap ,of the direct-current diversion device. The ?total kill of fish moving upstream, including 289 sea lampreys, was 1,016, or 1.3 percerz•. Th.is river 'had presen•:ed a serious problem in .the operation .of an al,tern•fing-current control device during previous seasons. In 1955, 85.5 percent .of three important species of fish were killed at the ,con•:rol structure. During 1956, •l•is mortM•ity was reduced to 8.1 percent by the operation of the direct-current equipment. INTRODUCTION The development and application of control methods to reduce stocks of sea lampreys in the Great Lakes is one of the major objectives of the Great Lakes Fishery Investigations. Several methods of sea lamprey control •Thi's study was eo,nduoted under the direorion of Le,o F. Erkk•la, Fishery Rese,aroh Biologist, .1M[•rquette, Mic•hi•an. 269 27O American Fish eries Society proached. Many had di'fficulty negoti'ating the restricted opening of the Electrical Fish • Barrier 271 trap funnels because their movements were involuntary. Observations of the reactions of fish to various componems of the electrical fields led to the development of the device described ...
Sea lampreys from the Lake Huron basin carried no external parasites and showed a fairly low degree of infection by internal parasites. The material examined represented three life‐history stages of the sea lamprey. Recently transformed downstream migrants (215 specimens) harbored only nematodes belonging to the genus Camallanus. The percentage of infection was 2.3. Active feeders from the lake (29 lampreys) revealed the highest degree of parasitism (31.0 percent) with the following parasites present: Echinorhynchus coregoni Linkins; Triaenophorus crassus Forel; and Camallanus sp. Among the 257 sexually mature upstream migrants (14.8 percent infected) Echinorhynchus coregoni and E. leidyi Van Cleave were the most common. Only occasional nematodes and cestodes were found, which fact indicates a failure of the lamprey to carry these parasites to the end of its natural life. Of the parasites observed, only the nematodes gave evidence of serious damage to the host. The study suggests that the role played by parasites in the natural control of the sea lamprey in its new habitat in the upper Great Lakes is of minor importance.
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