488 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



restrung on wires and suspended side by side at 

 a designated spot on the raft. 



Just prior to planting the Mill Creek oysters on 

 the bottom, a sample of undisturbed oysters was 

 measured. Their mean height and length were 

 compared with the mean height and length of oys- 

 tei-s that had been disturbed and cleaned each 

 month. Little difference between the two groups 

 was found. 



In our experiments the shell growtli of oysters 

 from Wareham Eiver was obser\ed from the time 

 they were first attached to the raft in the fall of 

 1956 imtil the raft was dismantled in 1958. Simi- 

 lar observations of growth were made on oysters 

 from Mill Creek which were attached to the raft 

 in the fall of 1957, then planted on the bottom in 

 the winter of 1958, and finally sold in the winter 

 of 1959. No measurements were taken from mid- 

 November to April because no appreciable shell 

 growth occurred during this period. Oysters on 

 the bottom of the same age and origin as those at- 

 tached to the raft were measured once each fall. 

 Since these oysters were on private grounds, their 

 disturbance was kept at a minimum. 



Monthly survival among the raft oysters was 

 recorded by counting the total number of live oys- 

 ters on one string. By selecting the same string 

 each month, any decrease in the total number of 

 live oysters from that counted the previous month 

 could be considered natural mortality. A year 

 after the raft oystere were planted on the bottom 

 a random sample was collected and the number of 

 live and dead (left valves only) oysters were 

 counted. The ratio of dead to the total number in 

 the sample was considered natural mortality. 



ANALYSIS OF RESULTS 

 GROWTH 



The shell growth i-ate of the eastern oyster of 

 the Atlantic Coast increases soutjiward and in the 

 Gulf of Mexico. The average lieight of oysters 



Table 1 



at the end of the setting year in Connecticut is 

 19 mm. (Loosanoff, 1946). Moore (1897) found 

 that by the end of the first season of growth oysters 

 of Chesapeake Bay measured 38 mm. in height, 

 whereas in North Carolina this size was reached in 

 3 months. Moore also observed that 7-month-old 

 South Carolina oysters measured 63 nnn. in height. 

 Galtsoti' and Luce (1930) working in Cieorgia, 

 observed 1 -year-old oysters ranging from 2-t nnn. 

 to 69 mm. Ingle (1950) reported that Florida 

 oysters reached 25.4 mm. in 5 weeks, wliile Butler 

 (1954) found oyster set that grew to 51 nun. in 

 height by the end of the year. Tlie fastest growth 

 was observed in Louisiana where 1'2-month-old 

 oysters reached 71 mm. in height (Moore and 

 Pope, 1910), although Butler (1954) observed 

 under special conditions at Pensacola (Fla.), a 

 growth of 76 to 101 mm. in 12 months. 



Our study shows that the growth of raft oysters 

 from Wareham River was fairly similar to that 

 observed by Loosanoff (1946) for tlie oy.sters 

 grown off the bottom at Milford Harbor (Conn.) ; 

 the mean height in successive years of 11, 49, and 

 72 mm. for tlie former compared to 19, 59, and 

 78 nnn. for the latter (table 1). In contrast, the 

 raft oysters from Mill Creek grew faster ; the mean 

 height was 28, 67, and 88 mm. 



The difference in growth of our Wareham River 

 and Mill Creek oysters was caused by the time of 

 setting of the oysters. Setting m Mill Creek oc- 

 curred in the middle of July 1957, and by Novem- 

 ber, wlien growth stopped, the mean height of 

 these oysters was 28 mm. (table 1, fig. 9). Setting 

 in Wareham River did not take place until late 

 August 1956, and the oysters averaged only 11 

 mm. in height when growth stopped in Novenil)er. 

 After the settingyear * shell growtli of botli groups 

 was about the same. The total annual increment 



I From time of settinp; to January 1 Is the setting year 

 January 1 to January 1 is tlie first year, etc. 



from 



Measured mean height and length {mm.), and number of oysters from Wareham Eiver, Long Island Sound, and 



Mill Creek at the end of growing periods 



' The information taken from: LoosanofT, Victor L., 1946, Qrowthofoystersof different ages in Milford Harbor. 

 ' .4t the end of the first year the Mill Creek stock was planted on the bottom. 



Proc. Nat. Shellfish Assoc, 1946, pp. 12-2r 



