SEA LAMPREY OF CAYUGA LAKE 



613 



Predators 



Numerous mammals and birds, a few reptiles, 

 amphibians, and fishes were cited as predators on 

 the sea lamprey by Surface (1899) . He gave defi- 

 nite evidence of predation on the sea lamprey for 

 the little green heron, the common water snake, 

 and minnows of the genera Rhinichthys and 

 Notropis. In Michigan, Applegate (1950) re- 

 ported that walleye, northern pike, brown trout, 

 raccoon, dogs, great blue heron, and sea gulls 

 preyed on sea lampreys. The sea gull was the 

 only predator of importance. 



Daily excursions along Cayuga Inlet through- 

 out the sea lamprey migratory and spawning sea- 

 son of 1951 and numerous visits during the 1950 

 and 1952 seasons, revealed amazingly little evi- 

 dence of predation on spawning lampreys. Lam- 

 preys are especially vulnerable to predation while 

 in the shallows of the tributary streams. It would 

 be easy for almost any of the common predaceous 

 animals to capture them. Nevertheless, the only 

 animal actually witnessed devouring a sea lamprey 

 was the common water snake, Natrix sipedon. 

 In addition, six partially eaten lamprey carcasses 

 were found along Cayuga Inlet during the three 

 seasons of study. They appeared to have been 

 killed by carnivores. 



The only evidence of predation on sea lampreys 

 in Cayuga Lake by fish was an unconfirmed report 

 by a fisherman that he had found a sea lamprey 

 in the stomach of a lake trout. Stomach analysis 

 of hundreds of fish from Cayuga Lake, especially 

 lake trout, have not produced a single instance of 

 predation on the sea lamprey. 



The only important predators on the sea lam- 

 prey in Cayuga Inlet are the small minnows that 

 feed on the eggs. At the time of egg deposition, 

 groups of these small fish gather just below the 

 downstream rims of the nests. When the eggs 

 are emitted, they quickly dart into the nest and 

 seize as many eggs as possible before being fright- 

 ened away by the spawners. Spawning lam- 

 preys never make an effort to drive these intruders 

 from the nest, but the spawning actions seem to 

 frighten the minnows. On June 4, 1951, the 

 stomachs of six blacknose dace, Rhinichthys 

 atratulus, contained numerous lamprey eggs. 



CONTROL METHODS 



Interrelationships between the sea lamprey and 

 their host species in Cayuga Lake are only par- 



498325 O— 59 8 



tially understood. In Lake Michigan and Lake 

 Huron this parasite is very destructive to food and 

 game fishes, and the sea lamprey is undoubtedly 

 the cause of the destruction of many lake trout 

 in Cayuga Lake. Their depredation on this fish 

 in Cayuga Lake is compensated in part by their 

 usefulness as an extraordinary, primitive creature 

 for study by students in neighboring educational 

 institutions. It is the writer's view that a pro- 

 gram for reduction of numbers of sea lampreys in 

 Cayuga Lake may be desirable, but that a supply 

 should be maintained for scientific use. 



Trapping operations in Cayuga Inlet have indi- 

 cated the feasibility of reducing and possibly 

 eradicating the Cayuga Lake population of sea 

 lampreys by capturing spawning-run migrants. 

 Also, the importance of extensive breeding and 

 nursery areas as a factor in the abundance of the 

 sea lamprey suggests the possibility of lowering 

 the population level by reducing the spawning 

 area available to them. Three methods of con- 

 trol appear to be practical: 



1. Construction of a small barrier dam across 

 Cayuga Inlet, 3 miles upstream from Cayuga 

 Lake, would cut off extensive spawning areas. 

 The initial expenditure would amount to several 

 thousand dollars, but in the long run the dam 

 would be more economical than traps or weirs 

 since a barrier dam requires little or no mainte- 

 nance. It blocks the migration of sea lampreys, 

 but permits migration of game fishes. A head of 

 1 }i to 2 feet should be effective under normal water 

 conditions. A dam similar in design to the U.S. 

 Geological Survey dam (fig. 11) would be suitable. 

 A better but more expensive structure was de- 

 scribed by Applegate and Smith (1950). An over- 

 hanging lip on the downstream side of the dam is 

 essential. 



2. An electromechanical weir and trap, similar 

 to the one operated on the Kewaunee River, Wis. 

 (Applegate, Smith, and Nielson 1952), should be 

 the most efficient. The major disadvantage of 

 this method is the expense. The device would 

 cost several thousand dollars to purchase and 

 install, and operational expenses would amount 

 to several hundred dollars each spring. 



3. Construction of a lamprey trap on the 

 downstream side of the U.S. Geological Survey 

 dam would provide an inexpensive control. This 

 method would limit the lamprey to about 3 miles 

 of spawning territory and bar it from 7 miles of 



