12 U. S. BUREAU OF FISHERIES. 



tunately, however, complete failure of the oyster set made it im- 

 practical to add to our knowledge in regard to the minimum or 

 optimum elevation for growth and survival, but data of value for the 

 determination of the correlation of temperature and oyster spawning 

 and setting were obtained. Later, at Milford, Conn., it was found 

 that the presence of very minute amounts of H2S causes spat to stop 

 feeding, and from this it follows that the presence of the gas is, at 

 the very least, highly disadvantageous. 



The work in the New Haven-Bridgeport area of Long Island 

 Sound, where once an important supply of northern " seed " oysters 

 was produced and where the sets have become alarmingly reduced, 

 consisted in the collection of data regarding temperatures ; spawning 

 of oysters; the occurrence, distribution, and development of larvse 

 and spat; and the effects on spat of various chemicals known to be 

 important pollutants. Data concerning the age and growth of spat 

 also were collected. The investigations revealed the fact that the set 

 of oysters was much above the average following a season in which 

 the oysters in harbors and inshore areas of the Sound spawned com- 

 paratively early. 



Oyster larvae were found in the Housatonic River for the first time 

 in the five seasons during which these investigations were carried on. 

 For a number of years there had been no oysters in this river until a 

 planting was made in the spring of 1922. The set was comparatively 

 good, but a very large proportion was destroyed by starfish and 

 drills, and to a considerable but uncertain extent by other adverse 

 factors. The set of oysters at the mouth of the Housatonic River 

 occurred during a time of lessened trade-waste pollution due to de- 

 creased manufacture and when water conditions presumably were 

 temporarily much better than usual. Because it was believed that 

 improved water conditions may have had a great influence on the set, 

 it seemed desirable that a survey be made at this time for compari- 

 son with conditions obtaining during periods of greater industrial 

 activity. In October, therefore, in cooperation with the Bureau of 

 Chemistry, an investigation was made of water conditions in the 

 Housatonic River and New Haven Harbor with regard to trade- 

 waste pollution with heavy metals, and also with regard to oxygen 

 content and alkalinity. From this work it appeared that conditions 

 were chemically decidedly worse in the optically clean Housatonic 

 River than in the obviously fouled New Haven Harbor. This was 

 most notably true with regard to copper, but also held for zinc and 

 dissolved oxygen. 



In the experiments with pollutants a copper salt was found most 

 destructive. A solution of copper chloride containing 10 parts per 

 1,000,000 of copper gave complete mortality of oyster spat under 

 conditions in which other metallic salts gave less mortality and the 

 control experiments nearly complete survival. 



An inquiry into the relationship between spawning and water tem- 

 peratures has been carried on for a number of years. At this stage 

 of the investigation the evidence indicates that fairly satisfactory 

 temperature conditions, viz, the attainment of 70° F., or higher, by 

 late July or early August, and the maintenance of about this tem- 

 perature for the few weeks required for spawning and setting, are 

 generally to be expected not only in estuaries but also in inshore areas 

 in the sound. Therefore, until conditions in the estuaries can be 



