marine animals discarded in their estimate, the 

 corresponding value is 171 x 10* (Schaefer 1965). 

 The range of estimates from this group-80 to 200 

 million metric tons-is understandable, in view of 

 limitations on basic scientific information now 

 available. Only Chapman's figure of 1,000 million 

 metric tons for existing technology appears out of 

 line in terms of the other estimates. 



If we consider together estimates based on 

 catch trends or present fishing patterns with those 

 which follow material through the food chain, it is 

 necessary also to consider man's technological and 

 economic limitations; the range then runs from 55 

 to 200 million metric tons (excluding Chapman), 

 with the majority less than 100 milUon metric 

 tons. 



Those estimates that are based on total primary 

 production differ in assumed amounts of carbon 

 fixed annually, in the ecological efficiency factor 

 employed, and the level of harvest. Much of this is 

 still controversial and our knowledge is simply 

 insufficient to make an intelligent choice among 

 differing views. Some of the confusion has resulted 

 from authors jumping back and forth between wet 

 weight, dry weight, fixed carbon, and total weight; 

 and it should be remembered that the amount of 



organic matter produced annually by photosyn- 

 thesis is still subject to much uncertainty. A 

 comparison of some of the estimates dealing with 

 this subject is given in Table 2. 



Selecting any author's starting value, it is 

 possible to develop a theoretical yield by trophic 



Table 2 



AVERAGE ANNUAL PRIMARY PRODUCTION 



OF ORGANIC MATTER 



(in dry weight) 



Steeman Nielsen 



Riley 



Zernov 



Skopintsev 



Wiborg 



Sverdrup and Fleming 



30 X 10' tons 



260 X 10' tons 



120 X 10' tons 



90 x 10' tons 



(70 to 140) X 10' tons 



(100 to 200) X 10' tons 



Source: Bogdanov (1966). 



levels for various ecological efficiency transfer 

 rates as indicated in Table 3. 



A more meaningful way of expressing the 

 problem would be in terms of the supply function 

 concept common to economic and business ana- 



Table 3 



POTENTIAL HARVEST OF THE SEA 



ESTIMATES OF POTENTIAL YIELDS' (PER YEAR) 



AT VARIOUS TROPHIC LEVELS, IN METRIC TONS 



Ecological Efficiency Factor 



Source: Schaefer (1965). 

 Output to predation at each trophic level. 



2 



NAS Committee estimates (approximately). 



VII- 11 



