Eight experiments aimed at improving methods for the village-based farming
of giant clams were conducted in the Solomon Islands, The experiments focus
ed on either improving the fitness of seed clams delivered to village farme
rs, assessing whether differential growth rates of seed clams in nursery ta
nks persisted during grow-out at farms, or testing the effects of alteratio
ns to the design of grow-out cages on the growth and survival of clams. We
found that Tridacna squamosa (Lamarck) 'seed' transferred from land-based n
ursery tanks to a floating ocean nursery (FON) for approximate to 3 months
at the end of the nursery phase were significantly larger than seed reared
only in land-based nursery tanks, Similarly, T, maxima (Roding) placed in a
FON for 2-5 months generally grew at a significantly greater rate than tan
k-reared 'seed'. However, the use of FONs did not improve survival. There w
ere no consistent differences in the growth and survival of fast- and slow-
growing seed of T. derasa (Roding) at village sites when slow-growing seed
were retained in the nursery until reaching a larger size. The survival of
T. maxima was enhanced significantly by placing an insert of smaller mesh (
a 'settlement ring') in grow-out cages for the first 2 months after deliver
y of seed to farmers. The settlement ring retained clams in cages until the
y found a suitable place to attach their byssal threads. Attempts to remove
the sediment which impedes the attachment of T, maxima to the base of grow
-out cages by perforating the substrate did not improve survival: the perfo
rated substrate resulted in poor attachment of clams and harboured predator
s (Cymatium spp.). The survival of T. crocea (Lamarck) was not improved by
'softening' the concrete base of grow-out cages to simulate dead coral rock
and to encourage the clams to burrow in the substrate. The survival of T,
crocea in grow-out cages was enhanced significantly by enclosing the cages
in fine mesh after the delivery of the seed clams to prevent predation and
disturbance by juvenile wrasse, Thalassoma spp. The experiments indicate th
at the critical stage for village farming of giant clams is during the init
ial weeks following distribution of seed. Further research is needed to imp
rove the survival of T. crocea and T. maxima during this phase.