66 MARINE FISHERIES OF NORTH CAROLINA 



favorable conditions, it seems conservative to use the average of 88 1 tons, 

 multiply it by the 16,500 square miles involved, and consider the resulting 

 i4j536,5oo tons as an estimate of the annual carbon production in North 

 Carolina waters.'^ 



The largest annual catch recorded for North Carolina is 224,457,000 

 pounds or 112,229 tons.^° Using 10 per cent as the proportion of carbon in 

 most living things, including fishes, this would represent 11,222 tons of 

 carbon or .08 per cent of the calculated basic production. 



This figure of .08 per cent depends on so many approximations that it 

 serves only to indicate the general magnitude of the productivity relation- 

 ship; however, my confidence in this is augmented by the fact that the 

 following, somewhat different approach gives a figure of .06 per cent. This 

 other procedure is as follows : 



1. Radiant energy reaching the earth's surface at Washington, D. C. 

 equals 341 g.cal./cm.Vday (Hand, 1941) or 124,465 g.cal./cm.Vyear. 

 Since the North Carolina coast is south of Washington and has approximately 

 2,800 hours of sunshine annually as compared to about 2,600 hours in Wash- 

 ington (from map data supplied by the U. S. Weather Bureau), this figure 

 for radiant energy is probably a little low for the region being considered. 



2. Riley (1941) rates the efficiency of net plant production in Long Island 

 Sound at 0.31 per cent. At such an efficiency rating the net plant production 

 from the above mentioned radiant energy would be 386 g.cal./cm.Vyear or 

 165 X 10^^ for the estimated 16,500 sq. miles of North Carolina coastal 

 waters. Since Long Island Sound is notably productive, the efficiency figure 

 used may be high. Perhaps it helps offset errors created by using the radia- 

 tion figure for Washington, D. C. 



3. Using a figure of 1,000 g.cal./g. for the energy content of raw fish (as 

 suggested in correspondence by Harden F. Taylor) the peak North Carolina 

 catch of 224,457,000 lbs. would yield 102 x 10^" g.cal. which is .06 per cent ^^ 

 of the basic productivity of 165 x 10^^ g.cal. 



The losses expected at successive links in the food chain must be recognized 



29. More precise estimates require, among other things, a greater knowledge of the details of 

 circulation discussed above. For example, the extent to which currents hold produced organisms 

 in the region or permit them to drain off may prove very critical. 



30. The winter trawl fishery makes large catches offshore around Cape Hatteras and docks 

 most of it in Virginia, whereupon it is listed in the Virginia, instead of the North Carolina 

 records. Pearson (1932) studied this fishery in 1930-31 during months when it was more or less 

 restricted to North Carolina's offshore waters and rated the yield at approximately 5,700,000 

 pounds. There are insufficient data to permit adding the proper share of the winter trawl catches 

 to North Carolina's annual yield. Due to high prices, they represent a large economic factor; 

 however, including them would not create an appreciable change in the poundage figures being 

 used for these ecological discussions. 



31. This percentage and the .08 per cent calculated above would both be slightly higher if an 

 attempt were made to account for the carbon content and energy value of the menhaden 

 involved, both of which are higher than average. 



