The use of Large Artificial Reefs to Enhance Fish Populations at Different Depths in the Florida Keys

Kruer, Curtis; Causey, Laura

...Like many other non-profit and governmental artificial reef programs around the Gulf of Mexico, the Florida Keys Artificial Reef Association (FKARA), organized in 1980, has functioned mainly as an opportunistic builder of reefs when sui table material or vessels were available. From 1981 to 1987 the FKARA supervised the placement of 35,000 tons of bridge rubble at 6 permitted sites, and the sinking of 5 vessels from 187' to 327' long from Key Largo to Key West (FKARA 1990). All materials were placed onto sandy bottoms. Although fish surveys have been conducted on several of these shallower rubble reef sites for years, available information is limited to relative abundance, general patterns of succession, and, to some degree, recruitment... A N.O.A.A. grant through the National Marine Fisheries Service, Marine Fisheries Initiative (MARFIN) program funded the 2 year monitoring project that followed unit placement in June of 1988 and the preparation of this descriptive report. The purpose of this study was to evaluate the potential for fishery enhancement of placing large prefabricated units and concrete rubble in different depths and locations off the Lower Florida Keys. The project was designed to produce useful information on the responses of fish to the introduction of specific types and profiles of large structures. Examined were production potential, locational differences, fishery value, and economics of two different types of artificial reef construction projects. Censusing adjacent natural bank reefs using standard methods allowed comparisons of community structure. Fishes were censused on 15 bridge rubble "patch reefs" placed from 1983 to 1987 at 2 locations in Hawk Channel for additional comparisons. The study's original objectives were: 1. Quantify the species composition, biomass and seasonality of fishes attracted and produced on large fabricated artificial habitats over a 24 month period. 2. Compare the colonization and community structure of reef fishes on the fabricated habitats to nearby natural reefs. 3. Evaluate the effects of reef siting at different water depths on species composition, recruitment, and biomass. 4. Separate fish communities into trophic levels to assess location of food source (e.g. water column, surrounding bottom, structure fouling community, etc.) 5. Through standard photographic techniques, document and quantify plant and invertebrate fouling communities as a function of substrate and water depth. 6. Determine if large, fabricated habitats can provide significant fishing opportunities. 7. Evaluate the economics of construction, transportation, and placement of artificial habitats to enhance fishery resources and fishing opportunities. Understanding how much artificial reefs increase fish numbers and biomass is important to wise fishery management and to the proper construction and deployment of artificial reefs (Bohnsack 1989). Basic knowledge of the results of reef building is critical to measure their value in a region as unique and significant as the Florida Keys, where future efforts could include additional concrete rubble reefs, clean steel vessels, and prefabricated concrete units. How artificial reefs should be used in a comprehensive fisheries (and people) management program in the Florida Keys National Marine Sanctuary will be resolved only through continued accumulation of ecological information on fish assemblages associated with reef habitats and documentation of various human uses. The use of structured, consistent methods for assessment of artificial habitats and the collection of long term population data on natural reef communities will facilitate important management decisions. As well, the ability to provide alternative fishing and diving sites through the creation of productive artificial reefs could assist in the management of people in one of the most popular fishing and diving locations in the United States and the world.