518 U. S. BUREAU OF FISHEEIES 



In order to determine the effect of the various environmental fac- 

 tors on the toxicity of copper sulphate, temperature, salinity, and 

 hydrogen-ion concentration were controlled or varied with interest- 

 ing results. A series of experiments where starfish 3 to 7 centimeters 

 in size were exposed to 500 parts per million of CuSOi, at tempera- 

 tures ranging from 10° to 35° C, show that exposure necessary to 

 kill decreases from 8 minutes at 10° C. to 1^ minutes at 35° C. 



A number of experiments were run testing the effect of pH within 

 the normal range, 7.5 to 8.4. There was a slight tendency for the 

 water with originally lower pH to be more toxic in a given concen- 

 tration. Individual susceptibility is so varied and the differences 

 so small that the results wer^ quite inconclusive. However, as soon 

 as the pH were artificially lowered below 7 the toxicity became much 

 more pronounced. Whether deaths were due to the copper ion alone 

 could not be determined, for the animals die upon prolonged exposure 

 to water high in hydrogen ions. Copper sulphate lowers the pH of 

 sea water due to its carrying out in the precipitate carbonate and 

 hydroxyl ions. When copper salts are added to acidified sea water 

 no precipitation occurs, and although the toxicity is greatly increased 

 we are dealing with an entirely different phenomena. 



The above factors are of considerable importance when practical 

 application of the salt is considered. There is variation in salinity 

 and hydrogen-ion concentration during each tidal cycle. Tempera- 

 ture varies with the seasons, depth of water, river discharge, and solar 

 radiation. A correlation of these factors, together with a lethal 

 concentration of the copper salt and a knowledge of the habits of the 

 starfish, may produce a workable method for control. 



Experiments vising coppe?' sulphate on the oyster teds. — Several 

 methods were attempted in order to see whether it would be prac- 

 ticable to use copper sulphate as a killing agent for starfish on the 

 beds. The first question was concerned with the method of applica- 

 tion. The following experiments were tried, and the results are 

 listed under each discussion. 



Experiment No. 1 was conducted on the Bluepoints Oyster Co. 

 grounds at Centerport, Long Island, August 4 and 5, 1931. One acre, 



6 to 10 feet deep, 300 feet from low-tide line, was chosen for the 

 experiment. A small hand dredge dragged for one minute caught 

 in three hauls an average of 13 starfish 6 to 8 centimeters in size. A 

 concentrated solution of copper sulphate in acidified sea water was 

 prepared by adding 80 pounds of copper sulphate to a barrel holding 



7 cubic feet of water. Using a hose, this solution was slowly pumped 

 over the bottom for 20 minutes at slack low tide. The entire acre 

 was covered by circles of the boat. The initial copper content of the 

 water was 0.05 part per million and the pH 7.8. Immediately after 

 the treatment there was 0.6 part per million of copper and a pH of 

 7.2 at the bottom. The next day there were virtually no starfish on 

 that area, in eight dredges there were three live starfish and no dead 

 ones. Oysters, scallops, and Crustacea showed no ill effects. The 

 water, pH, and copper content of the water were normal. Some of 

 the tops of the sea weed and grass were killed, but the roots were 

 unaffected and the grass survived. 



Experiment No. 2 was conducted on the Andrew Eadel Oyster Co. 

 grounds at Oyster Bay, L. I., August 16 and 17, 1931. The area 



