HYDROGRAPHY OF THE MARINE WATERS 67 



in considering the significance of these percentage figures. A predator is 

 seldom able to assimilate more than lo per cent of the over-all production of 

 its food organisms (see Lindeman, 1942); so the losses through successive 

 levels of the food chain are somewhat as follows: 



The weight of all primary consumers is less than 10 per cent of the basic 

 production. Examples: oysters which feed on microscopic drifting plants 

 and menhaden which feed largely on such plant plankton. 



The weight of all secondary consumers is less than 10 per cent of the 

 weight of primary consumer's or less than i per cent of the basic production. 

 Example: mackerel which feed on small drifting Crustacea which in turn 

 feed on microscopic drifting plants. 



The weight of tertiary consumers is less than 10 per cent of the weight of 

 secondary consumers or less than o.i per cent of the basic production. Ex- 

 ample: Blue fish which feed on small fish that are secondary and primary 

 consumers. 



Obviously, other things being equal, a fishery should be more efficient if 

 centered on species low in the food chain, as in agricultural practices where 

 we eat primary producers such as wheat and primary consumers such as beef 

 cattle. In this respect relatively high yields might be expected in North 

 Carolina, for the fishery is characterized by species low on the food chain, 

 such as menhaden which comprised over 80 per cent of the large 1939 catch; 

 yet the harvest is more of the order to be expected at the tertiary consumer 

 level. With menhaden, oysters, clams, shrimp, shad and many other low-level 

 consumers abounding in North Carolina, there appears to be ample hydro- 

 graphic and biological support for the hope that a considerably greater sea- 

 food production might be realized by improved management and resource- 

 use techniques. 



The present North Carolina harvest is not low by comparison with other 

 fishery areas. From 1923 to 1945 the smallest annual catch was 86,214,000 

 pounds in 1932, which equaled 8.2 lbs. /acre for these coastal waters, and the 

 largest annual catch was the 1939 yield of 224,457,000 lbs., representing 

 21.3 Ibs./acre. On Georges Bank, most important of the famous New Eng- 

 land fishing areas, the annual yield from 1923 to 1945 ranged from 7 to t,^, 

 lbs. /acre/year (Clarke, 1946); however, with fish like haddock and others 

 high on their respective food chains dominating the catch, there is little 

 reason to expect a high return. The range of 8-2 1 Ibs./acre/year is also com- 

 parable to the commercial production in large lakes. Rounsefell (1946) 

 reports a range from 29.72 pounds per acre for 10,000 acre lakes to 1.40 

 pounds per acre for 25,000,000 acre lakes. These lake figures exhibit a con- 

 sistent negative correlation between lake size and yield per unit area which 

 Rounsefell (1946) attributes to the relative amount of shoal shoreline waters. 

 Marine habitats are usually characterized by vast areas with proportionately 



