TROPHIC RELATIONSHIPS 



185 



the balanced (respiration equals production) systems or 

 altering their intracommunity trophic structures to some 

 degree, probably a bit of each. This raises a fundamental 

 fisheries question of general application as well as for 

 Enewetak: What level of harvests can be sustained through 

 tapping an otherwise climax system or by altering it? 

 Marshall has used the term "ecological sustainable yield 

 (ESY)"* in referring to the harvest potential in this sense. 

 (For a further development of this point see Marshall, 

 1979 and Marshall, 1985.) 



Determining the yield potential as just discussed, i.e., 

 through excess production, by tapping into the cycles of 

 balanced systems, or by altering the systems, is not possi- 

 ble under present methodologies. Even if rates for these 

 categories were well-known, the width of the confidence 

 limits and the variability expected for such basic steps in 

 the food web are of far greater magnitude than ultimate 

 yields. Consequently, attempted calculations of the latter 

 would be meaningless. Thus the only possibility for an 

 appraisal of how much can be taken, i.e., the ESY, is to 

 review actual harvest experiences. Summarizing data from 

 reefs and adjacent shallows elsewhere, Marshall (1985) has 

 suggested a generalized harvest potential of 4 to 5 metric 

 tons km plus miscellaneous gleanings from off the reef. 

 While this may represent a norm, some reports show 

 much higher yields. For example, for American Samoa, 

 Wass (1980) indicated 27 tons km"^ while Hill (1978) 

 indicated 12 tons km~^. It now appears that the potential 

 commonly may run well over 20 tons for some locales yet 

 be even less than 1 ton for others (Alcala and Luchavez, 

 1982; Alcala and Gomez, 1985). 



Though the research done to date at Enewetak has 

 contributed very little to the yield question in any direct 

 sense, the atoll could be used for further meaningful stud- 

 ies by experimentally fishing replicate knolls in the lagoon 

 and critically observing the response to different fishing 

 pressures. As in any climax environment, a properly 

 managed harvest may serve as a culling process to the 

 benefit of the system. Such observations at Enewetak, 

 which has not been fished to any extent since early in the 

 1950s, could throw further light on this f>ossibility. Hiatt 

 and Strasburg (1960) offer a good foundation for such 

 research in a publication rich in information on feeding 

 habits and ecological relationships of Marshall Island reef 

 fishes. Johannes, who was so involved in promoting basic 

 ecological research at Enewetak, has become a leader in 

 compiling useful life history information, often stressing 

 insights gained from native fishermen (Johannes, 1978). 



While the question of fisheries potential is a promising 

 area for study, we would not wish to raise undue expecta- 

 tions but would close by quoting Kinsey and Domm (1974) 

 who take a conservative view: 



This is not to be confused with the maximum sustainable 

 yield (MSY) commonly used in fisheries and dealing with 

 recruitment/growth/mortality patterns for single, or small 

 numbers of interacting, species. 



Coral reefs generally have been found to exhibit a high 

 turnover of carbon but a relatively small zero net gain. 

 Thus, while they have typically one of the highest known 

 naturally occurring levels of productivity. It is apparent that 

 they cannot tolerate any heavy cropping. Removal of 

 biomass not only involves the removal of carbon from the 

 system, but other accumulated and recycling elements. 



REFERENCES 



Alcala, A C, and E. D. Gomez, 1985, Fish Yields of Coral Reefs 

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and T. F. Luchavez, 1982, Fish Yield of the Coral 



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Atkinson, M., S V. Smith, and E. D Stroup, 1981, Circulation in 

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— , and M. B. Gerber, 1979, Ingestion of Particulate Organic 

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HiU, H. B., 1978, The Use of Nearshore Marine Life as a Food 

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