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This work reports on the effects of cage mesh size and tidal level placement upon the growth and survival of the hard clam, Mercenarla mercenaria (L.), and the surf clam, Spisula solidissima (Dillwyn), In the coastal waters of Georgia. Surf clams (N = 50 per cage) and hard clams (N = 100 per cage) were each planted in replicated (N = 2) cages constructed of 3 mm, 6 mm, 13 mm and 19 mm mesh vexar plastic at various tidal levels. Cages were deployed by partial burial at the mean and the spring low water marks. At termination of the surf clam trial (6 months), there were no significant differences in survival determined for clams planted in different mesh cages at either tidal level or for clams grown in equivalent mesh size cages between tidal levels. There were significant differences In clam size with surf clams at the spring low water growing significantly larger than those at the mean low water mark. There were also significant differences In surf clam growth between different mesh size cages. Surf clams from 6 mm cages were smaller than those from other cages, while the largest clams reared were in the 13 mm and 19 mm mesh cages. Hard clam trials (15 month duration) illustrated that cage mesh size induced significant differences in sur· vlval of hard clams. Significantly fewer clams survived In 19 mm mesh cages than in cages of smaller mesh at both tidal levels. No significant differences in hard clam survival were detected among other mesh sizes nor between tidal levels; neither were significant dif· ferences between tidal levels determined for equivalent mesh sizes. Significant differences in hard clam growth were determined for clams grown in different mesh size cages and between tidal levels. Clam growth was greater at the spring low water mark. Clams grew larger in 3 mm mesh cages, least In 13 mm mesh cages with no significant differences In growth in the 6 and 19 mm mesh cages. Statistical analyses (t-tests) Illustrated differences in clam growth among replicates at the spring low water mark. Growth may have been reduced in one set of cages as a result of cage excavation by currents. In Georgia, hard and surf clam growth was found to be dependent upon cage mesh size. Clam survival was Independent of cage mesh size as long as the initial size of the seed animals was greater than the mesh size of the cage. Controlling mortalities and growing a crop to marketable size in as short a time period as possible are the essential ingredients for a successful (clam) mariculture operation. Many methods of protecting juvenile clams from predators have been developed. For instance, innumerable sizes, shapes and types of 29 cages or boxes, tent structures, baffling devices, fencing, gravel or shell aggregate, or various combinations of these have been employeed in an attempt to control clam predation (e.g., Castagna and Kraeuter, 1981; Kraeuter and Castagna, 1980; Menzel et a/., 1976). Most of these methods are site specific in their 1 Walker and Heffernan: The Effects of Cage Mesh Size and Tidal Level Placement on the Gr Published by The Aquila Digital Community, 1990 30 Walker, R.L., and P.B. Heffernan effectiveness. For instance, the use of gravel aggregate has proven very successful in. the eastern shore area of Virginia (Castagna and Kraeuter, 1977); whereas, it was not successful in the waters of Long Island, New York (Flagg and Malouf, 1983), Chesapeake Bay (Haven and Loesch, 1973) or in Florida (Menzel eta!., 1976). Cage culture, either floating, placed on the bottom or partially buried into the bottom, is the common method of growing clams. Yet, there are no reports on the optimum mesh size of the cage. The purpose of this research was to determine the effects of cage mesh size upon the growth and survival of the hard clam, Mercenaria mercenaria (L.) and the surf clam, Spisula solidissima (Dillwyn) for environmental conditions in the coastal waters of Georgia. Hard clams are of commercial irnportarwe and are presently being farmed in the coastal waters of Georgia, while the surf clam has shown potential as an aquaculture species (Goldberg, 1980; Krzynowek and

northeast gulf science

The Effects of Cage Mesh Size and Tidal Level Placement on the Growth and Survival of Clams, Mercenaria mercenaria (L.) and Spisula solidissima (Dillwyn), in the Coastal Waters of Georgia