SURVIVAL AND GROWTH OF JUVENILE FLUTED GIANT CLAMS, TRIDACNA-SQUAMOSA, IN LARGE-SCALE GROW-OUT TRIALS IN THE SOLOMON-ISLANDS

Two large-scale experiments were conducted with juvenile Tridacna squa mosa at coastal village sites in the Solomon Islands to provide robust estimates of survival and growth during grow-out. Juveniles were rear ed to similar to 24 mm shell length (10(-11) months) in land-based tan ks and then transferred to subtidal sites near villages for grow-out f or 8 months. During the first experiment, which started in 1993, survi val varied greatly among sites, ranging from 7% to 83%. Exposure ('fet ch area') and geographic location had a significant influence on survi val, indicating that adverse weather conditions affected mortality rat es. Inserts made of 5-mm galvanized mesh ('settlement rings') fitted t o the inside perimeter of grow-out cages significantly reduced loss of clams from cages after transfer to villages, Growth varied from 2.3 t o 8.6 mm month(-1) and was significantly, positively correlated with t he number of clams surviving in the cages. During the second experimen t, which commenced in 1994, survival was greater and less variable, ra nging from 42% to 83%. Average growth also improved, ranging from 4.0 to 7.2 mm month(-1). Growth was positively correlated with water flow, and negatively correlated with Secchi disc visibility and the number of predatory ranellid gastropods found in the grow-out cages, A weak n egative relationship between growth and survival occurred during the s econd experiment. Modifications to aquaculture protocols in 1994 were evaluated in a series of concurrent experiments conducted at the Villa ge sites. Grooves in the bases of cages, support of clams using pieces of coral, and retention of 'settlement rings' for 4 instead of 2 mont hs had no effect on survival and growth of the clams. However, surviva l of juveniles preconditioned in the ocean was significantly higher th an those reared exclusively in tanks. On the basis of these two experi ments, the mean time required to grow T. squamosa from 24 to 50 mm she ll length, a size suitable for sale to the aquarium market, was only 5 to 7 months. Our results reveal that village-based fanning can be eco nomically feasible in the Solomon Islands, provided reliable hatchery facilities are available.