on the stream bottom . The type of device is 

 chosen according to stream conditions, and ad- 

 justments of equipment are made in accordance 

 with experiences in each stream . 



Chemical control. --The reduction of 

 sea lamprey stocks by the prevention of spawn- 

 ing has the disadvantage that benefits are not 

 to be expected until the program has been un- 

 derway 4 to 6 years . At any one time the 

 stream contains the larvae from that number 

 of previous spawnings . A procedure that can 

 kill all larvae in a single operation, on the 

 other hand, gives almost immediate benefit 

 (only the parasites in the lake remain). In 

 recognition of the need for shortening the time 

 needed to reduce the numbers of sea lampreys, 

 the Hammond Bay Fishery Laboratory in 1953 

 started a screening program in an attempt to 

 find a compound lethal to ammocoetes in con- 

 centrations harmless to fish. 



Among the 4,600 compounds tested in 

 the original screening program, 8 were dis- 

 covered that exhibited strong differential tox- 

 icity toward larval lampreys, and of these, 2 

 gave particular promise. These 2 chemicals 

 were subjected to detailed testing to learn 

 their effects under different physical and chem- 

 ical conditions and on species of fish other than 

 the rainbow trout and bluegill employed in the 

 original screening. Toxicity studies of structur- 

 ally related chemicals brought to light 4 

 additional compounds of promise. 



The progress of these chemical studies 

 to the field-testing stage was slow and burdened 

 with numerous setbacks --some expected, others 

 unexpected. A major difficulty has been the ar- 

 rangement for the synthesis of various chemicals 

 and the development of satisfactory standards 

 of purity. Tests had to be made (by contract 

 with the Wisconsin Alumni Research Foundation) 

 of the effects of the compounds on birds and 

 mammals. Formulation s (emulsions, solvents) 

 had to be developed and metering devices ob- 

 tained and checked. Still further delays were 

 occasioned by the unanticipated sensitivity of 

 some compounds to changes in water conditions, 

 the nature of which has not been exactly deter- 

 mined. Despite all these problems raceway 

 tests were started in late 1956 and large-scale 

 field testing is scheduled for 1957. 



Growth of the control program 



After the researches at the Hammond 

 Bay Laboratory had led to the development of a 

 practical electrical barrier for blocking sea 

 lamprey runs, it was decided that the initial 

 control experiments should be made on Lake 

 Superior, the only lake that still carried a suf- 

 ficiently large population of lake trout to support 

 a commercial fishery. This strategy was in- 

 tended to serve two purposes: prevention of the 

 collapse of still another fishery; preservation 

 of lake trout stocks that could be used in the 

 restoration of Lakes Huron and Michigan. In 

 accordance with this plan, barriers were in- 

 stalled in 10 Lake Superior tributaries before 

 the start of the 1953 run and the control activities 

 were transferred from the Hammond Bay Labor- 

 atory to the Marquette field station, under the 

 direction of Erkkila. 



Whatever benefits might have accrued 

 from the small-scale control programs of 1953 

 were lost when operations had to be suspended 

 in mid-June, the barriers dismantled, and the 

 equipment stored. The threat of ruinous budget 

 cuts in fiscal year 1954 that forced this suspen- 

 sion of operations fortunately did not materialize. 



The lamprey runs on the U.S. shore of 

 Lake Superior were brought under "full" control 

 in 1954 when the 44 barriers in operation (table 2) 

 blocked all known spawning runs . Actually, the 

 control was not complete. A few short break- 

 downs occurred, and the discovery of new runs 

 in later seasons indicates that some spawning 

 may have been overlooked. It can be said, 

 nevertheless, that very little lamprey spawning 

 has taken place in U. S. tributaries of Lake 

 Superior subsequent to 1953. 



The records of the rate of increase in the 

 abundance of sea lampreys in Lake Superior em- 

 phasize the urgent need for effective control. 

 The numbers of spawning-run individuals cap- 

 tured in 30 streams that contained barriers in 

 1954-56 were: 



1954 

 1955 

 1956 



- 4,922 



- 8,823 



- 15, 753 



These figures make it seem likely that the lake 



