22 U. S. BUKEAU OF FISHEEIES 



was 1,500, and from the second, which was heavier, 4,000. After the 

 spat had attained their summer growth, they were easily detached 

 from the tiles without injury and planted as single seed oysters; in a 

 few years they will have developed into " select " stock, the most val- 

 uable product produced in this fishery. 



The location and arrangement of the various collectors had an 

 effect on the time and condition of tide when and depth and vertical 

 range at which setting takes place, and valuable data on these points 

 were collected. Shells and rocks scattered about the harbor also 

 were covered with spat, and from a small bar near the brush plantings 

 over 100 bushels of gravel, heavily set with oysters, were collected. 



The countless millions of seed oysters produced as a result of the 

 incomplete restoration of this harbor evidence the value of these inshore 

 areas to the oyster industry and the necessity of protecting them 

 from overfishing and pollution. 



Life-history studies. — -Spawning records were obtained from three 

 lots of ripe oysters, of 10 bushels each, kept under close observation 

 in a float. In each experiment, almost all of the oysters spawned 

 vigorously and simultaneously. Spawning occurred at 24.1°, 22°, 

 and 23° C., when the tide approached high-water mark. Records of 

 salinity and hydrogen-ion concentration were made at the same time. 

 The oysters on the spawning beds in shallow and deep water became 

 ripe much sooner than usual this year and discharged their spawn on 

 about the 6th and 13th of July. 



Plankton collections were made in Milford Harbor and Long Island 

 Sound for the purpose of determining the abundance, distribution, 

 and growth of the free-swimming oyster larvas prior to setting. The 

 collections made from 1921 to 1924 gave evidence of a strange disap- 

 pearance of the larvae from the time they were one or two days old 

 until they were nearly ready to set. Similarly, careful pumpings and 

 tows made in 1925, from the surface of the water to within a few 

 inches of the bottom, contained very few oyster larvae of the inter- 

 mediate sizes. From observations of the behavior of artificially prop- 

 agated larvae of these sizes it was apparent that they were not only 

 clamlike in structure but in habit as well, and capable of plowing 

 their way through sand and loose dirt by means of a long, muscular 

 foot. Several sections of bottom, about one-half inch thick, were 

 taken up near one of the spawning beds, placed in one of the hatch- 

 ing tanks, and supplied with a good stream of water. After several 

 hours, an examination of the bolting-silk net placed at the overflow 

 revealed many of the long-sought, intermediate-sized larvae, though it 

 was impossible to determine whether they had been on the bottom 

 or merely lying between the sand grains when the samples were col- 

 lected. The discovery of this interesting habit enables us to under- 

 stand better the relationship between spawning beds and setting areas 

 and the effect of tides, waves, and currents on the distribution of 

 the larva?. 



By arranging floating and stationary spat collectors from the bot- 

 tom of the channel to high-water mark, the following observations 

 on "setting" were made: First, that attachment of the greater pro- 

 portion of larvae occurred with the beginning of flood tide and contin- 

 ued for about two hours. Second, that the vertical distribution of the 

 spat took place from the bottom (30 feet below the surface) to within 



