Huron a large population of trout and other 

 predators existed in 1930, but sea lampreys 

 virtually eliminated them by the early 1940s. 

 Alewives were abundant in Lake Huron by the mid 

 1950s. In Lake Superior, they are not yet abun- 

 dant because of the large number of predators 

 remaining and because of the cold water. 



In Lake Michigan large predators were almost 

 gone when the alewives were first found there in 

 1949. By 1956, they were abundant throughout 

 the Lake and, during the early 1 960s, the number 

 of adults more than doubled each year. The 

 population reached a peak in 1966-67. As they 

 increased, yellow perch were crowded from off- 

 shore areas. 



The best control for alewives is the predator. 

 The introduction of coho salmon in Lakes 

 Michigan and Superior suggests this species may be 

 the most effective predator the lakes have ever 

 known. The coho, introduced by the Michigan 

 Conservation Department in 1966, has had a 

 surprising growth rate. The mature fish average of 

 12 pounds may be reached in one year. Lake trout 

 normally require 1 1 years to reach 1 2 pounds. 



However, the introduction of salmon may 

 result in a further imbalance of the ecology of the 

 Great Lakes. 



C. Eurasian Milfoil (Myriophyllum Spicatum) 



This species of aquarium plant, probably intro- 

 duced into Chesapeake Bay by discarding a house- 

 hold decoration, becomes a nuisance when it 

 forms extensive beds that interfere with boating, 

 swimming, and fishing. Dense beds of milfoil 

 create muddy bottoms by serving as setthng basins 

 for silt particles. Extensive beds damage oysters 

 and clams by reducing water circulation and 

 cutting oxygen supplies to them. It was estimated 

 in 1964 that about 100,000 acres of the Bay and 

 its tributaries were infested with milfoil, although 

 some estimates ran as high as 200,000 acres.*" 



Milfoil usually grows in depths less than eight 

 feet, but has been found at 12 feet. It grows best 

 in fresh water but has shown a tolerance of up to 

 15 parts per thousand sahnity, or half the concen- 

 tration of seawater. 



The Rivers and Harbors Act of 1965 designated 

 Eurasion Milfoil a major noxious aquatic plant and 

 authorized the Corps of Engineers to investigate 

 methods of control and eradication. 



The University of Maryland'" has conducted 

 experiments to test milfoil as poultry or cattle 

 food. Results so far show it to be unfavorable as 

 poultry food, but as good as high-quality hay for 

 cattle. However, beginning in 1964 a disease has 

 infected the milfoil in Cheasapeake Bay which 

 threatens to eliminate it as either a nuisance or a 

 use. As the milfoil recedes in Chesapeake Bay, 

 other aquatic plants such as water chestnuts 

 (Trapa nutans) and sea lettuce (Ulva ulvaceae) 

 appear to be taking its place. 



D. Water Hyacinths (Eichornia crassipesj 



For several years the growth of water hyacinths 

 has been an acute problem in South Atlantic and 

 Gulf Coast States. These floating plants choke 

 waterways and obstruct navigation, recreation and 

 fishing. Added nutrients to coastal and estuarine 

 waters appear to increase the plant's proliferation 

 and that of a similar pest, alligatorweed. 



Figure 14. Water hyacinth jam in a Florida 

 waterway. (U.S. Army Corps of Engineers 

 photo) 



In 1958 legislation'*^ first provided for control 

 and progressive eradication of the water hyacinth, 

 alligatorweed, and other obnoxious aquatic plant 

 growths from the navigable waters, tributary 

 streams, connecting channels, and other allied 

 waters in the States of North Carolina, South 



Chesapeake Bay Case Study, report by Trident 

 Engineering Associates to the National Council on Marine 

 Resources and Engineering Development, Oct. 20, 1967. 



42 



Rivers and Harbors Act of July 3, 1958. 



ni-47 



