1322 



Mitchell, Philip H. 1914. 



Oxygen requirements of shellfish. Bull. Bu. Fish, Washington (1912) 32: 

 207-222. 



Most quahogs failed to remain open for any length of time in these experiments, 

 thus only a few reliable measurements of oxygen consumption could be made. 

 These showed a rather low oxygen intake. At 24°C the following data were 

 obtained from quahogs of different sizes: 91 g, 1.01 mg/hr , 1.08 mg/hr, and 

 0.64 mg/hr; 150 g, 0.78 mg/hr; 470 g, 2.24 mg/hr. Oxygen used per hour per 

 gram dried weight was: 91 g clam, 0.41 mg; 150 g, 0.221 mg. This is less 

 than half the amount of O2 used by oysters of comparable weight at 24°C. 

 Closed quahogs used no O2. Voluntarily closed clams did use 02, which was 

 interpreted as meaning that even when apparently closed they take in water 

 by opening very slightly. At 24°C apparently closed clams of medium to 

 large size took up 0.29, 0.61, 0.46, and 0.43 mg O2 per hr. The smooth shell 

 apparently takes up little, if any, O2 , but empty shells, considerably broken 

 in opening, used a distinctly larger amount of 02 than the clams that were 

 clamped shut. - J.L.M. 



1323 



Mitchell, Roger. 1974. 



Studies on the population dynamics and some aspects of the biology of 

 Mercenaria mercenaria (Linne) . Ph.D. dissertation, Facultv of Science, 

 Department of Oceanography, University of Southampton, England, 2 p. 

 (abstract) . 



Hard clam has become established in parts of Southampton Water and the Solent 

 on the south coast of England, probably from deliberate introduction in 1925. 

 Absence of the species along the west shore of Southampton Water and its 

 exclusive distribution to the east in the Solent is explained partly by 

 hydrographic conditions which control larval transport. Young clams were 

 concentrated in shell gravel ridges. High clam density at some sites may have 

 been caused by elimination of competing native species by extremely cold 

 winters. Distribution of dominant year classes appeared to be correlated with 

 summers of above average water temp and certain conditions of river flow. 

 Good growth at sites where conditions were below optimum was attributed to 

 utilization of metabolic reserves normally required for gametogenesis and 

 spawning. Planktonic larvae were found from May to Sept in Southampton Water. 

 There was evidence that this population has become adapted to spawn at lower 

 temp than the ancestral stock. Warming of upper Southampton Water by power 

 station effluent may have contributed to establishment of the species. 

 Seasonal biochemical composition and condition index of sexually mature and 

 immature clams were very similar. It was concluded that this cycle probably 

 was linked more closely to water temp and availability of food than to state 

 of gonads. Distribution and growth in relation to sediment type, and 

 differences in biochemical content of early postlarvae and older clams are 

 mentioned, but not described. - J.L.M. 



1324 



Mitchell, Roger. 1974. 



Aspects of the ecology of the lamellibranch Mercenaria mercenaria in British 

 waters. Hydrobiol. Bull. 8: 124-138. 



Hard clams have been introduced into British waters several times. The first 

 live specimen was taken in the Humber River in 1884. Stocks in Southampton 

 Water and the Solent probably were derived from a small planting in the River 

 Test in 1925. It is found in sediments ranging from almost pure shell gravel 

 to sand-gravel-mud mixtures of up to 75% mud, but not in soft mud or clay, and 

 in salinities from 24 to 35°/oo. Densities per unit area are much higher than 

 those reported from the United States, up to 160 clams of commercial size per 

 m2. This may be due in part to elimination of competing native species by 

 severe winters. Its absence in some parts of the area may be caused by toxic 

 effects of industrial wastes and to easterly bias of tidal currents flowing 

 down the estuary. It is suggested that the present distribution in the 

 estuary is caused by recruitment from spawning in the River Test, and that the 

 population will not expand unless another spawning colony is established to 



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