46 U. S. BUREAU OF FISHERIES 



setting. A large number of oystermen availed themselves of the 

 opportunity to obtain these data and used them to advantage l)y plant- 

 ing shells at the proper time and place. It is planned to continue this 

 practice and if possible to extend it to a larger area. 



Control of starfish. — Observations on propagation and' feeding of 

 starfish in Long Island Sound were continued. The fact that star- 

 fish were responsible for the destruction of the greater part of the 

 •early oyster set in the summer of 1937 clearly demonstrates the im- 

 portance of these studies for their control. It was found that star- 

 fish spawned on or about June 15 at a temperature of 15.0° C. 

 (59^ F.). Setting began on July 7-8, and continued until September 

 •20. The heaviest setting occurred from the middle of July until the 

 middle of August. As in the case of the oyster spat, the newly set 

 starfish were more abundant in shallow water although setting took 

 place at all the depths from low water mark to 70 feet. 



Experiments on chemotropism of starfish were concluded in the 

 fall of 1937. These experiments sustained the conclusions arrived at 

 in. 1936, when the largest part of the experimental work was done, 

 tliat the cliemical sense of starfish is poorly developed. Usually a 

 starfish does not detect the presence of food until it comes in actual 

 contact with it. 



It has been the general practice of oystermen to use boiling water 

 or steam to kill starfish brought up by mops, an expensive proce- 

 dure because of the large quantities of fuel used to maintain water at 

 tlie boiling point. In the belief that water of much lower tempera- 

 ture would kill starfish, a series of experiments was undertaken to 

 determine the mininnmi lethal temperature for these animals. It 

 was found that a temperature of 50° C. (122° F.) was sufficient to 

 kill the starfish and that the use of boiling water is therefore 

 unnecessary. 



Although it is well known that starfish do not occur in water of 

 low salinity, the limits of tolerance for this species have not been 

 determined with accuracy. Experiments undertaken to provide this 

 information disclosed considerable individual variations in the ability 

 of starfish to withstand brackish water. When sul)jected to a salin- 

 ity of 14.00 parts per thousand some of the starfish died in 3 days 

 while others survived 13 days. The limit of tolerance is probably 

 around 16.00 parts per thousand, for in this dilution of sea water 

 some animals were kept alive 2 months. 



At the request of Virginia oystermen a survey of the distribution 

 and abundance of starfish in the lower Chesapeake Bay was made 

 i)i March. The investigation revealed that starfish were confined to 

 the area south of a line drawn from New Point Comfort to Cherry- 

 stone Island. The largest concentration was found near York Spit 

 Light. Other areas of heavy infestation were found 3 miles south- 

 east from Back River, 3 miles north of Little Creek, and in the 

 vicinity of Old Plantation Light. The starfish population was not 

 uniformly distributed, being on muddy bottoms where there was an 

 abundant supply of small clams, Mulinia lateralis, upon which they 

 were feeding. No starfish were found on oyster bottoms located in 

 the areas of low salinity. In April, with the rise of water in the 

 rivers emptying into the Chesapeake Bay, the starfish population 

 withdrew toward the mouth of the Bay. 



