M. mercenaria male 1/16 to 1/8 inch long were received. Sites were chosen at 

 which salinities would not be likely to drop below 20°/oo. Of 8 separate 

 plantings, 3 experiments failed for various reasons and a 4th succeeded only 

 partially. All hybrids in that experiment died by 30 May 1961, but 278 of 

 600 M. mercenaria survived and were 5/16 to 11/16 inches long. At 

 St. Petersburg salinities rarely go below 30°/»= or above 34. By 19 February 

 1961 hybrids had tripled or quadrupled in size and M. mercenaria had doubled. 

 Mortality had been negligible and virtually confined to M. mercenaria. Clams 

 were shifted to extra boxes to avoid overcrowding. By mid-June 1961 hybrids 

 had reached maximum lengths of 1 1/4 inch, M. mercenaria a max. of 1 3/4 inch. 

 About 25% of the hybrids had survived, but 1/2 of the M. mercenaria were lost 

 when the screen was lost and clams were washed out or eaten by predators. 

 Those that survived outside the box were larger than those in boxes. At 

 Sarasota young clams brought earlier from Milford grew about one inch from 

 1 April to 5 August 1960, when they were killed by fresh water. From 

 November plantings, hybrids grew to max. lengths of 1 1/2 inch and 

 M. mercenaria to a max. of 1 1/4 inch by mid-June 1961. Some of these clams 

 were planted on open bottom enclosed with chicken wire, and grew faster than 

 those in boxes. At Sebastian, on the east coast, salinities are somewhat 

 below optimum range for hard clam. Seven days after planting, 50% of the 

 hybrids and 10-15% of the M. mercenaria were dead. In the next 7 days no 

 further mortality was seen. By mid- June hybrids had grown to max. length of 

 1 1/4 inch and M. mercenaria to a max. of 1 3/8 inch. At Oak Hill, also on 

 the east coast, by 19 January 1961 hybrids and M. mercenaria had about 

 doubled in size. By 15 May 1961, both lots were one inch long. Hybrid 

 survival was about 90% and M. mercenaria about 83%. Salinities range from 

 23 to 32°/°o except during unusually heavy runoff. - J.L.M. 



2046 



Woodburn, Kenneth D. 19 62. 



Clams and oysters in Charlotte County and vicinity. Fla. State Bd. Conserv. , 

 Mar. Lab., FSBCML 62-12, 29 mimeo p. (originally mimeo 1 Aug 62, reissued 

 Mar 65) . 



Mercenaria campechiensis was being harvested extensively from productive 

 natural beds along the inside of Gulf of Mexico barrier islands. Recorded 

 production of hardshell clams in Fla. began in 1880, increased significantly 

 in 1908 with exploitation of large beds in Collier and Monroe Counties near 

 the Ten Thousand Islands, grew steadily until the peak year 1932, remained 

 high through most of the second world war, then fell to a low by 1950. 

 Subsequently, production increased modestly, then jumped rapidly in 1962 as 

 intensive harvesting began in Charlotte County and vicinity. The increase 

 was made possible by new markets in the Middle Atlantic states. In Fla., hard 

 clams usually are processed into chowder or canned minced clams. Spawning 

 condition does not affect quality of meats as markedly as it does in oysters, 

 and no closed season is necessary. Hard clams do not tolerate salinities 

 below 20°/oo. Large canals draining raw upland and emptying into coastal 

 rivers and bays have increased salinity variations, and have created 'lower 

 salinities at times of heavy runoff. An extensive survey of 18 major areas 

 found hard clams at only 4, where salinities and substrate were favorable. 

 Clams were most concentrated where firm, sticky mud bottom and seagrass were 

 found. In one part of Gasparilla Sound, which supports one of the best hard 

 clam beds in Fla,, large clams were growing at 15 to 20 clams/yd2 . Commercial 

 clam beds most vulnerable to dredging in the intracoastal waterway 

 development were identified. - J.L.M. 



2047 



Woodburn, Kenneth D. 196 3. 



Survival and growth of laboratory-reared northern clams (Mercenaria 

 mercenaria) and hybrids (M. mercenaria X M. campechiensis ) in Florida 

 waters. Proc. Natl. Shellf. Assn. 52: 31-36. 



Recorded hard clam production in Fla. began in 1880, increased significantly 

 in 1908 when large clam beds near the Ten Thousand Islands on the west coast 

 were discovered, peaked in 1932, remained high through most of WW II and 

 plummeted to a low in 1950. Production has increased modestly since then. 



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