Giant clams (faisua)
Giant clams (faisua) are magnificent animals and it's always a pleasure to see one of these beauties on the reef. They are large, colorful and, surprisingly, the clams are part animal and part “plant”. That's because giant clams, like corals, have plant-like cells (zooxanthellae) in their tissues that produce free food for the clams. When a clam opens its shell and spreads out its pretty mantle, it exposes these solar panels (the zooxanthellae) to the sun to make food, like a plant unfolding its leaves.
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| Photo by Larry Basch. |
At the same time, the clam also gets some food by drawing water through its siphon and filtering out any tiny food particles (zooplankton). Perhaps that's why giant clams grow so large – they have two very different ways to get food.
We have two native species of giant clams in our local waters, Tridacna maxima and T. squamosa, which look fairly similar. They grow to about 12-15 inches in shell length, although most found today are much smaller because the larger ones have been over-harvested. The largest and most famous species of giant clam (T. gigas), which grows as big as a large suitcase, does not occur in our waters.
Because giant clams need sunlight, they inhabit shallow, clear waters down to about 60 feet deep. They grow very slowly; one local clam was 18 years old. They spawn repeatedly over their life span and release millions of eggs each time they spawn, but most young clams do not survive, so the adults have to live a long time and spawn many times to insure that the population survives. Larval clams swim in the water for about a week, then settle permanently onto the reef to grow.
The clams are a favorite food item throughout the South Pacific and their accessibility in shallow waters and slow growth make them susceptible to overfishing. That is very much the case in American Samoa, where few remain on many of our reefs. There is a growing concern that our population of giant clams may be getting too few and far between to spawn successfully.
Partly for that reason, there has been an interest in growing these clams in hatcheries to supply markets for food and the aquarium trade. DMWR has operated a hatchery here for many years and tried to encourage local production by supplying small clams for local 'farmers' to grow them on their reefs. That effort has met with limited success for several reasons. Considerable dedication is needed because it may take years to grow the clams to a commercial size, and the clams have to be protected from poachers and predators. And there are always fa'alavelave events that call for contributions of giant clams if anyone has some. In general, giant clam mariculture here has usually supplemented family needs rather than create a commercial business.
Harvest
regulations in American Samoa are: giant clams taken for personal consumption
must be at least 6 inches in shell length, or if sold, a license is required
and giant clams must be at least 7 inches in shell length and sold with
the clam still in its shell.
P. Craig, NPS