190 Conservation Department 



diet, then to grow from five grams to 200 grams in weight — or to 

 increase 195 grams, would require 195 grams divided by 

 29% = 672.41 grams or 1.48 lbs. of this food. But the natural food 

 of the lamprey is fish blood, and from the tables in Lusk's Nutri- 

 tion, p. 579, the average nutritive value of fish flesh is less than 

 half that of the liver and skim-milk, hence it would require at 

 least twice as much blood, probablv much more, for the lamprey 

 to gain 195 grams, that is 672.41x2=1344.82 grams or 2.96 lbs. If 

 there were one thousand lampreys in a lake — and more than that 

 have been caught from Cayuga lake some years — it would require 

 at least three thousand pounds of fish blood to bring them to 

 maturity. Every one would probably agree that this would be 

 a heavy toll to pay, when the only return is a limited amount 

 of fish bait supplied by the ammocoetes ! 



Possibility of Ridding a Lake of Lampreys. — In the economic 

 struggle with insects, and other creatures that claim a part of 

 the products of the earth and waters that man wants for his 

 own sustenance, man's success in overcoming his competitors de- 

 pends largely upon the completeness of his knowledge of their 

 life history. 



With practically every living thing there is some time in the life 

 cycle when they are most easily destroyed. It is evident to every 

 one that it would be hopeless to try to catch and destroy all the 

 lampreys scattered throughout the waters of a lake. It would 

 be equally hopeless to try to dig all the larvae out of the mud- 

 banks along the spawning stream ; but there is one time when 

 the lampreys that have reached maturity are particularly exposed, 

 and that is when they run up from the lake into the small streams 

 to lay their eggs. If weirs or traps are put across those spawn- 

 ing streams and all the lampreys caught and destroyed before 

 any eggs were laid there would be no new generation started. 

 In streams where high dams have been constructed and no 

 fishways arranged for, the fish that ascend the streams to spawn 

 soon disappear above the dams. Also in some streams so much 

 pollution has been poured into them that all the young fish are 

 destroyed. It looks absolutely simple on the face of it to deal 

 with the lampreys. But it is far from simple. If even one pair 

 got through and laid the thousands of eggs carried by the female, 

 enough of the eggs would hatch, and young survive to restock 

 the lake in a few years. 



Again in the mud-banks of the spawning streams there are four 

 to five generations of larval lampreys growing up to enter upon 

 the predatory life, and every year for four to five years a genera- 

 tion would mature and go down to the lake and remain from one 

 and a third to three and a third years. 



If then every lamprey going up to spawn were caught and 

 killed, this must be done for from six to eight years to get the 

 last pair. Of course the more that are prevented from spawning 

 the fewer would the predatory lampreys be, but to eliminate them 

 absolutely would require the time mentioned. Furthermore as the 



