control technique. Routine stream treatments are carried out with TFM or 

 with TFM plus a small amount (1-4%) of powdered Bayer 73. The addition of 

 Bayer 73 reduces up to one-half the amount of TFM required and greatly 

 reduces the cost of treatments. A granular form of Bayer 73, which settles 

 to the bottom before chemical release, is also used in diff icult-to-reach 

 areas during treatment with TFM, but is more frequently used as a collect- 

 ing tool in surveys. At proper concentrations the chemicals destroy sea 

 lamprey larvae without significantly affecting other fauna and flora. 



A defined range of concentrations, dependent on alkalinity, pH, and 

 temperature, must be maintained for several hours throughout the treatment 

 area. Field bioassays, conducted in mobile units, identify the lowest con- 

 centration of TFM that kills 10U% of sea lamprey larvae in 9 hr or less and 

 the highest concentration that does not kill more than 25% of the test 

 species (usually rainbow trout, Salmo gairdnerii ) in 18-24 hr (Kanayama, 

 1963). These criteria provide safety factors at both extremes. Stream con- 

 centrations are maintained between these limits by controlled applications 

 at several stations on the stream. The defined range can vary between 1.0 

 and 2.3 mg/liter toxicant on low alkalinity streams (10-20 mg/liter as 

 CaC0 3 ) and between 6.7 and 17.0 mg/liter toxicant on high alkalinity 

 streams (163 mg/liter as CaC0 3 ). 



Sea lamprey control with lampricides was initiated in Lake Superior in 

 19b8 and expanded to Lake Michigan in 1960, to Lake Huron in 1966, and Lake 

 Ontario in 1971. The first "round" 1 of treatments was completed in Lake 

 Superior in 1961; in Lake Michigan in 1966; in Lake Huron in 1970; and in 

 Lake Ontario in 1972. The total number of treatments since 1958 exceeds 

 1,000. 



In Lake Superior, where the control program has been in operation for 

 the greatest number of years and where its effectiveness has been most care- 

 fully evaluated, sea lamprey abundance has been reduced by about 90%. A 

 quantitative measure of sea lamprey abundance has been obtained from counts 

 of mature (spawning run) sea lampreys reaching assessment barriers. 

 Numbers of mature sea lampreys in the Lake Superior spawning runs declined 

 sharply in 1962, the year after the first round of stream treatments had 

 been completed (Figure 6). The decrease was accompanied by a marked de- 

 cline in the incidence of fresh sea lamprey wounds on lake trout and later 

 by an improved survival of lake trout to older age and larger size. Equiva- 

 lent quantitative data are not available for Lakes Huron and Michigan, but 

 the responses of sea lamprey and fish populations to control efforts have 

 been similar to those in Lake Superior. 



The Great Lakes Fishery Commission is concerned that the control pro- 

 gram is singularly dependent on chemicals, primarily TFM. Only one chemical 

 manufacturer submits bids. Costs have risen sharply to $13.18 kg, and we 

 use over 45,360 kg a year. Early in the program it was necessary to treat 

 each stream only once every 4 years. However, the average ammocete is now 



*A "round" denotes that all known sea-lamprey-producing streams tributary 

 to that lake have received one chemical treatment. 



224 



