CalCOFI Reports, Vol. 30, 1989 - California Cooperative Oceanic ...

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SYMPOSIUM INTRODUCTION CalCOFl Rep.,Vol. 30,1989 give it a try. Perhaps Gary Davis of the National Park Service, who presents that paper, is correct when he quotes Machiavelli. But that would be giving it away. When you have read his paper you may agree, not just with his hypothesis, but with the assessment of the risks involved in any unusual, and therefore uncomfortable, solutions. My own professional interest, man-made reefs, is well debated by Ray Buckley from the Washing- ton State Department of Fisheries and Jeff Polovina, NMFS-Hawaii. Marine fish hatcheries are discussed by Bill Rutledge of Texas Parks and Wildlife, who tells us they can work, and by Alec MacCall, NMFS, who insists they cannot. I hope you find these papers as stimulating as I have found working with the authors. John Grunt 36
POLOVINA: ARTIFICIAL REEFS: BENTHIC FISH AGGREGATORS ColCOFl Rep., Vol. 30,1989 ARTIFICIAL REEFS: NOTHING MORE THAN BENTHIC FISH AGGREGATORS JEFFREY J. POLOVINA Southwest Fisheries Center Honolulu Laboratory National Marine Fisheries Service, NOAA 2570 Dole Street Honolulu, Hawaii 96822-2396 ABSTRACT The potential for artificial reefs to substantially increase standing stock of marine resources is considered. Three sources - the Japanese artificial reef program; relationships between fishery production and the area of natural habitat for several fisheries; and population dynamics - offer evidence that artificial reefs do not substantially increase the standing stock of marine resources. RESUMEN Se considera el potencial de 10s arrecifes artificiales para aumentar sustancialmente el stoc4 disponible de 10s recursos marinos. Tres fuentes de evidencia: el programa de arrecifes artificiales japods, la relaci6n entre producci6n y Area del hAbitat natural de varias pesquerias, y la dinimica de poblaciones, indican que 10s sustratos artificiales no aumentan sustancialmente el stock disponible de 10s recursos marinos. DISCUSSION Artificial reefs can be excellent fish aggregators, but they do not effectively increase standing stock. This position will be supported with three types of evidence: first, with observations from the Japanese artificial reef program; second, from the relationship between habitat and fishery production; and finally from considerations of population dynamics. Between 1976 and 1987, the Japanese spent U. S. $4.2 billion to construct and deploy 6,443 artificial reefs, covering 9.3% of the ocean bottom from shore to a depth of 200 m (Yamane, in press). But despite this enormous volume of artificial reefs deployed in coastal water, there has not been any measurable increase in coastal fishery landings (Japan: Statistics and Information Department 1984). Studies specifically investigating the impact of the artificial reefs have generally not documented any significant increases in fish production that can be attributed to the reefs (Kawasaki 1984; Kakimoto and Okubo 1985). After three visits to Japan and numerous discussions with people involved in all aspects of the Japanese artificial reef program, I be- lieve the real benefit of the reefs is that they aggregate wide-ranging fishes close to shore so they can be harvested by fishermen with small vessels and thus keep the fleet of small vessels economically viable. Outside of Japan, artificial reefs have not been deployed on a large enough scale to evaluate their effectiveness in increasing standing stocks. However, examining the relationship between habitat and fishery production can provide estimates of the level of fishery yield per area of habitat that might be expected from appropriately designed and sited artificial reefs. One example is penaeid shrimp: worldwide fishery yields range from 8 to 200 kg/ hectare of intertidal nursery habitat (Turner 1977). In the case of artificial reefs, yields are measured in production per unit of reef volume. Thus if a square meter of intertidal habitat is assumed to also contain about a meter of vertical structure, grass, or mangrove, then these yield figures are equivalent to 0- 0.02 kg/m2. Another example is the coral reef systems, from which .fishery yields have been reported in the range of 5-20 t/km2 (Marten and Polovina 1982). If one square meter of coral reef habitat is conservatively assumed to be equal to one cubic meter of reef volume, then production per volume of reef habitat is 0.005-0.02 kg/m3. To put this production-per-unit-of-habitat volume in perspective, I will relate it to an example from California, where recent annual commercial landings for rockfishes are about 15,000 metric tons (MT) (California Department of Fish and Game 1987). I will assume that the average figure for fishery production per habitat volume from coral reef fisheries, 0.01 kg/m3, can be applied to rockfishes. I will further assume that artificial reefs can be ten times more effective than natural habitat that might include barren or unproductive areas. With a level of fishery production of 0.1 kg/m3 of habitat volume, it would require 15 million m3 of artificial reefs to increase the annual rockfish catches by 10%. At the extremely low cost of $10/m3 of reef for construction and deployment, this would cost $150 million. To put 15 million m3 of artificial reefs into perspective, consider a space 100 X 50 m, about the 37
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AUTHOR-TITLE INDEX, 1983-88 CalCOFl
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SUBJECT INDEX, 1983-88 CalCOFl Rep.
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130' 125' 120" 115' 1100 1 I I 1 1
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CalCOFI Reports, Vol. 30, 1989 - California Cooperative Oceanic ...

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