8 U. S. BUREAU OF FISHERIES. 



sulphuric acid in ?• 0.01 per cent solution, 18 per cent mortality oc- 

 curred in 5 days. Logwood in a 0.1 gram per liter solution exhioited 

 only a moderate fatality — 25 per cent in 12 days — but was evidently 

 more harmful than the rate of fatality indicated, for it proved so 

 obnoxious to the spat that they remained closed a large portion of 

 the time. Such an elfect would be very harmful to oysters in any 

 stage, and probably would be fatal to the larvse. 



LarviB succumb to poisoning more readily than do spat, but they 

 are much more difficult to manipulate and observe. With large 

 larvae, copper-salt solutions in strengths varying from 10 to 0.5 parts 

 of copper per million, and zinc or lead salts in solutions of 10 parts 

 of the metal per million proved fatal in less than a day. In the 

 controls the greater portion of the larA^^e lived into the second day 

 and frequently many of them survived for several days longer. 



Embryos were used in only one poisoning experiment with a 

 copper-salt solution of 10 parts of the metal per million. In this 

 the embryos suft'ered no apparent ill effects for a. little over an hour. 

 The next morning, however, all were dead and disintegrating.^ No 

 marked mortality was observable at this time in the control, in which 

 considerable numbere of the embryos lived until night. 



These experiments make it clear that copper, even in veiy small 

 amounts, is a serious menace to the oyster industry, and especially to 

 that A-ital part of it — seed production. If anything is to be done to 

 bring the estuaries back to their former high productivity the pre- 

 vention of the discharge of copper-containing wastes should be the 

 first step taken. Zinc, lead, strong acids, and logwood, among the 

 substances tested, should also be guarded against. J. W. Sale, water 

 and beverage laboratory. United States Department of Agriculture, 

 while investigating for the bureau, found all of these substances in, 

 or being discharged into, the waters of industrialized rivers and har- 

 bors opening into the Sound. The metals, in particular, have not 

 only been found in the effluents from industrial plants, but have 

 also been revealed by analyses of water samples taken from the 

 rivers and harbors of the region. Copper, indeed, has been found in 

 solutions of just under 0.5 parts per million where oysters formerly 

 abounded. It is altogether probable that at some stage of the tide 

 this strength may, on occasion, be equaled or even slightly exceeded. 



Although something can be and has been accomplished by plant- 

 ing oysters in harbors and rivers solely for spawning purposes, yet 

 imless the pollution of these waters can be prevented the source of 

 any really extensive set must be sought in the Sound, where far the 

 greater portion of the oysters is located. 



In the Sound, oyster lots are roughly graded into two classes — 

 inshore and offshore. Offshore lots frequently possess advantages 

 over inshore lots as holding grounds, as otherwise, with the increased 

 depth and other drawbacks, they would not be kept stocked with 

 oysters when inshore lots are available. However, from the funda- 

 mental standpoint of seed production — that is, as a location for 

 oysters to produce the gi^eat and early abundance of larvse needed 

 for " heavy " and sufficiently early sets — they are almost hopeless. 



