462 RILEY [CHAP. 20 



well as the Great Lakes fisheries (Rawson, 1952). Thus the theoretical results 

 are at least credible, although not much confidence can be placed in them until 

 physiological coefficients and descriptive aspects of the food chain have been 

 investigated more fully. 



Although absolute values have little meaning, it may be of some interest to 

 examine relative changes in potential tuna biomass with different levels of food 

 availability. The quantities of herbivores and forage animals that were used in 

 the example above were first doubled and then halved, and the tuna biomass 

 was computed according to equation (39). Table II shows that a fourfold 

 change in herbivores and forage animals leads to an approximately fifteen-fold 

 variation in potential tuna. 



Table II 



Potential Tuna (Skipjack) Biomass in g/1000 m 3 Computed for Three Levels of 

 Accompanying Populations of Herbivores and Forage Animals 



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systems. Biometrika, 44, 27-42. 

 Clarke, G. L., 1938. Seasonal changes in the intensity of submarine illumination off Woods 



Hole. Ecology, 19, 89-106. 

 Clarke, C. L. and D. J. Zinn, 1937. Seasonal production of zooplankton off Woods Hole 



with special reference to Calanus finmarchicus. Biol. Bull., 73, 464-487. 

 Cashing, D. H., 1958. The effect of grazing in reducing the primary production: a review. 



Rapp. Cons. Explor. Mer, 144, 149-154. 

 Cashing, D. H., 1959. On the nature of production in the sea. Min. Agric. Fish. Food, 



U.K., Fish. Invest., 22 (6), 1-40. 

 Dawes, B., 1930. Growth and maintenance in the plaice {Pleuronectes platessa). Part I. 



J. Mar. Biol. Assoc. U.K., 17, 103-174. 

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Biol. Assoc. U.K., 17, 877-947. 

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Mer, 14, 210-227. 

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Biol. Assoc. U.K., 29, 97-137. 

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 tion and its control. J. Mar. Biol. Assoc. U.K., 20, 407-441. 

 Holmes, R. W., M. B. Schaefer and B. M. Shimada, 1957. Primary production, chlorophyll, 



and zooplankton volumes in the tropical eastern Pacific Ocean. Inter- Amer. Trop. 



Tuna Comm. Bull., 2, 127-169. 

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