unqualified success of all four trials permitted 

 the release of the compounds for use in an 

 experiment to reduce stocks of sea lampreys, 

 first in Lake Superior and then in the lower 

 Lakes. Of the two compounds, TFM was 

 selected for general use because of the lesser 

 quantities required to achieve concentrations 

 lethal to sea lampreys. 



The discovery and development for practical 

 field use of toxicants that could destroy sea 

 lampreys without inflicting significant damage 

 on other fishes was the culmination of 4 years 

 of research at the Biological Station in Ham- 

 mond Bay (established in 1950) on northern 

 Lake Huron, Thousands of chemicals were 

 evaluated. When the selective properties of 

 halogenated nitrophenols were discovered, 

 these properties of physiological effects of 

 the compounds were studied in series of de- 

 tailed bioassays. Next, tests were completed 

 in raceways before trials in natural streams 

 were undertaken. 



The development and subsequent field use of 

 a selective larvicide placed the staff of the 

 sea lamprey unit temporarily in the unhappy 

 position of operating at considerable cost along 

 two lines, one of which almost certainly would 

 be abandoned. Before the selective toxicant 

 was discovered, the one available method that 

 gave promise of effective control was the 

 blocking of spawning runs of sea lampreys by 

 electrical barriers installed in streams below 

 the spawning areas. This control method had 

 the major shortcoming that no results interms 

 of a reduction of parasitic-phase sea lampreys 

 in a lake could be expected until all spawning 

 streams of a lake had been blocked 4 to 7 

 years, the apparent length of larval life in the 

 stream. The barriers also had operational 

 weaknesses. Their effectiveness was in- 

 fluenced greatly by details of installation that 

 had to be worked out stream by stream; on 

 occasion, extensive and costly modifications or 

 new installations were required. The barriers 

 also rarely blocked the run completely. Opera- 

 tions were interrupted occasionally despite 

 the precaution of standby generators intended 

 to start autonnatically when the regular power 

 source was interrupted. More damaging were 

 abnormally high stream levels which could 

 nnake the traps on structures ineffective from 

 a few hours to as long as several weeks. Still 

 another difficulty that required much attention 

 was the mortality of fish at some barriers. 

 These kills were reduced somewhat by im- 

 provements of barrier design but more im- 

 portantly by the development and installation 

 in the more troublesome streams of a direct- 

 current (DC) diversion device situated just 

 downstream fronn the main alternating-current 

 (AC) barrier. 



During nnuch of the period when the con- 

 struction and operation of electrical barriers 

 were being improved toward maximum effi- 

 ciency and new units were being added to the 



barrier systems, the work was carried on with 

 full knowledge that electrical control might 

 soon be superseded by chemical control. The 

 extensive equipment, except that required to 

 monitor changes in sea lamprey stocks, would 

 then be surplus hardware. Yet, no choice ex- 

 isted; a control method of known promise could 

 not be abandoned until the soundness of the 

 alternative chemical control could be estab- 

 lished beyond reasonable doubt. 



As the chemical treatments of streams ex- 

 panded, barrier operations were reduced (table 

 1). After 1960, the electric barriers served 

 solely as monitoring devices. Barriers on 

 Lake Michigan were reduced to three to save 

 money for use in chemical treatments. Now 

 that treatments are well advanced on Lake 

 Michigan the number of barriers is to be in- 

 creased to at least six to provide broader 

 coverage. 



The chemical treatments did not proceed 

 without certain difficulties and failures. The 

 development and handling of proportioning 

 equipment raised problems, and field pro- 

 cedures had to be worked out for pretreatment 

 surveys and bioassays, the actual treatment, 

 and the posttreatment check. Causes of failures 

 needed to be learned and remedies developed, 

 A few of the early treatments had to be re- 

 peated, but continued experience largely elimi- 

 nated failures and led to a highly efficient 

 routine. Among the major advances were the 

 construction of mobile bioassay laboratories, 

 the development of rapid and accurate proce- 

 dures for determination of the concentration 

 of larvicides in stream water, the fabrication 

 of equipment for the automatic recording of 

 the passage of dye used in studies of stream 

 flow, and the establishment of effective radio 

 communication among groups engaged in the 

 treatnnent of large stream systenns. 



The personnel of the control unit, indeed the 

 entire staff of the Biological Laboratory at 

 Ann Arbor awaited anxiously the final proof 

 of the effectiveness of chemical control on Lake 

 Superior in the form of sharply reduced catches 

 of spawning-run sea lampreys at the electric 

 barriers. Enough streams had been treated by 

 1961 to raise Sonne hope of a decrease of the 

 run that year; the 1961 run actually was at a 

 record high of 67,230 lampreys (table 2), The 

 real drop came in 1962 when the total catch of 

 lampreys (9,122 individuals) declined 84,4 per- 

 cent from the preceding year. This new low 

 level continued in 1963 and 1964. 



Even though the sea lamprey stock of Lake 

 Superior should be and, it is hoped, can be re- 

 duced further, the present control clearly has 

 benefited the lake trout populations. The lake 

 trout stocks, bolstered by large-scale planting 

 of fingerlings, have reached levels of abundance 

 in some parts of Lake Superior equal to those 

 in years preceding the lamprey's penetration 

 into the Lake. Abundance of lake trout is not 

 equally great in other areas but is increasing 



