Shellfish Remnants

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This is a duplicate of Fun with Clams. Just provide a link to [[Fun with Clams]] instead of putting up the same material twice.
Marty


Fun With Clams: Three Experiments with Tidacna sp. Valves

Experiment 1: Throwing the Tridacna

Issue: In initial inspection of photographs showing Clambushes 1 and 2 at the Seven Site, it appears that well over half the valves are lying with their concave sides up. Does this high proportion of up-facing valves indicate purposeful placement, for example in order to catch water?

Null hypothesis: The aerodynamics of Tridacna valves is such that when thrown a short distance (as would happen after one has eaten the contents), the valves tend to land face-up in disproportionate numbers.

Experiment: I tossed a small (ca. 20 cm. long) T. gigas valve (obtained in Chuuk in the 1970s) one hundred times over a distance of about eight feet and a height of about six feet, with the valves landing on dirt with a light and sporadic cover of ivy and other low plants, tallying the number of times it landed face-up, face-down, and on edge.

Observations: Sixty-two times out of one hundred, the valve landed face-up; Thirty-seven times it landed face-down. In one instance it landed and remained on edge. Thus:

Face-up: 62% Face-down: 37% Edge: 01%

Often the valve would land on an edge and tip “backward” to fall face-up; falling the other way occurred much less often. In a few occasions the valve even landed face down and immediately flipped over to face up.

Conclusion: The null hypothesis is confirmed.

Experiment 2: Cooking in a Tridacna Valve

Issue: In Chuuk, and probably elsewhere in the Pacific, Tridacna valves were traditionally used to contain liquid medicines as these were being warmed on a fire before application or consumption. Could cooking in a fire, and/or the application of water to the inside of a Tridacna valve while the valve is in a fire, cause the sort of splitting and spalling observed in the valves of Clambush #1 at the Seven Site?

Hypothesis: Cooking in a Tridacna will cause spalling and other damage similar to what was observed in Clambush #1.

Prior observation: A number of the valves in Clambush #1 show severe trauma near the byssal orifice, with either or both the exterior layers and/or the interior mother-of-pearl layer spalled back from the ragged edge of a break, as well as splitting and shattering.

Experiment: The same T. gigas valve used in the tossing experiment was placed in a wood and charcoal fire, filled with water. As the water evaporated, the valve was refilled. In total, the valve was refilled seven times before it became too cracked to hold water. The fire was then allowed to die down and cool, without moving the valve.

Observations: By the time of the second filling, the outer surface of the valve had begun to blacken and char. By the fifth filling, a serious latitudinal crack had developed. By the seventh filling the valve could no longer hold water. When the fire had died down the valve had split in several directions and literally fell apart into five pieces, which broke further upon being touched. The valve had become very fragile, and crumbled easily. Parts of it were blackened, others dark gray, others chalky white (especially in the interior). Although in some places the mother-of-pearl broke away from the other layers, there was nothing like the spalling observed in the Clambush #1 specimens. Nor was the damage confined to the vicinity of the byssal orifice; the entire valve was damaged.

Conclusion: Burning and cooking do not appear to cause the sort of damage observed in Clambush #1.

Caveat: Other ways of cooking (for example, suspension over the fire rather than laying the valve in it), fires of different strengths, and other variables may affect the breaking pattern and result in something more like what is observed in the clambush.

Experiment 3A: How Much of a Load?

Issue: Clambush #1 at the Seven Site apparently represents some seventeen Tridacna, presumably carried in from elsewhere, perhaps the lagoon margin. Would a load of seventeen such clams be too much for a lone castaway to carry?

Calculations:

Step 1: Of the entire collection of individual valves from Clambush 1, twenty-two were complete enough to make it possible to obtain fairly accurate full-valve weights. All were weighed, and found to range from 79 to about 340 grams, with an average weight per valve of 175.3 grams. This means an average clam weight (valves only) of 350.6 grams.

Step 2: Lacking a meaty Tridacna, a good-sized Cherrystone Clam was obtained from a local supermarket ($0.29 donation to TIGHAR). Its live, wet weight was found to be 136 grams. The clam was then boiled until it opened (about five minutes), and with some feeling of guilt the meat and innerds were removed and discarded. The wet empty-shell weight of both valves was found to be 94 grams. The valves were then dried over a charcoal fire for two hours. The dry(er) weight was 92 grams. Note, this drying, on a rack about 15 cm. above the fire, did not cause cracking or any other noticeable change to the shell.

Thus in this particular Cherrystone clam, the dry shell accounted for 68% of the total weight, while the meat accounted for 32%

Step 3: Assuming a meat-shell ratio in Tridacna that is similar to that in Cherrystones, then a Tridacna with a 350.6 gram shell should have weighed about 515.6 grams when alive and wet.

Step 4: The seventeen clams in Clambush #1 thus should have collectively weighed about 8.765 kilograms.

Step 5: One kilogram equals 2.2046 pounds.

Step 6: It follows that the clams in Clambush #1 should have weighed about 19.32 pounds, which should not have been beyond the capacity of an individual to carry, assuming he or she had something to carry the clams in.

Note: Clambush # 1, with all its individuals wrapped in padding, now resides comfortably in an archive box.

Experiment 3B: Refined Study of Projected Meat Weight, Clambush #1

Issue: Clambush #1 at the Seven Site apparently represents some seventeen Tridacna, probably species crocea. The clams were presumably carried in from elsewhere, perhaps the lagoon margin. Would a load of seventeen such clams be too much for a lone castaway to carry?

Calculations:

Step 1: Of the entire collection of individual valves from Clambush 1, twenty-two were complete enough to make it possible to obtain fairly accurate full-valve weights. All were weighed, and found to range from 79 to about 340 grams, with an average weight per valve of 175.3 grams. This means an average clam weight (valves only) of 350.6 grams.

Step 2: Scott Russell of Saipan procured five live Tridacna, by diving on Saipan’s reef. These were almost certainly T. gigas. Russell provides the following documentation on his specimens:

Clam 1: Length = 15.5 cm width = 7 cm thickness when closed = 7.5 cm

Total weight (shell and meat) = 595 g. Total weight of meat = 54 g. Total weight of meat minus guts = 48 g.

Clam 2: Length = 17.5 cm width = 9 cm thickness when closed = 10.5 cm

total weight = 1,010 g total weight of meat = 125 g total weight of meat minus guts 113 g.

Clam 3: Length = 17 cm width = 9.5 cm thickness when closed = 10.5 cm

total weight = 980 g. total weight of meat = 133 g. total weight of meat minus guts = 128 g.

Clam 4: Length = 20 cm width = 11 cm thickness when closed = 11.5 cm

total weight = 1.239 g. total weight of meat = 139 g. total weight of meat minus guts = 133 g.

Clam 5 Length = 18 cm width = 10.5 cm thickness when closed = 10.5 cm

total weight = 933 g. total weight of meat = 128 g. total weight of meat minus guts = 119 g.

From which we can derive the following averages:

Average total weight: 951.4 g Average weight of meat: 115.8 g. Average weight of edible meat: 108.2 g

Thus in the average Tridacna gigas in Russell’s sample the wet shell accounts for about 88 % of the total animal weight, with the innerds accounting for about 12% and edible meat adding up to about 11%.

Earlier, I had procured a good-sized Cherrystone Clam from a local supermarket ($0.29 donation to TIGHAR). Its live, wet weight was found to be 136 grams. The clam was then boiled until it opened (about five minutes), and with some feeling of guilt the meat and innerds were removed and discarded. The wet empty-shell weight of both valves was found to be 94 grams. The valves were then dried over a charcoal fire for two hours. The dry(er) weight was 92 grams. Note, this drying, on a rack about 15 cm. above the fire, did not cause cracking or any other noticeable change to the shell.

In this particular Cherrystone clam, the dry shell accounted for 68% of the total weight, while the meat accounted for 32%. Since the shell of a Cherrystone is much thinner than that of a Tridacna, this ratio is not nearly as relevant to Clambush #1 as are the ratios derived from Russell’s T. gigas, but what is relevant is the Cherrystone’s loss of 2 grams – about 2% of its weight – to drying. Assuming that Russell’s clams, if dried, would have lost a similar amount of weight, (average 19.02 grams) then we derive the following corrected averages:

Average total wet weight: 951.4 g Average dry shell weight: 816.58 g (951.4-19.02-115.8; 86% of total wet weight) Average weight of meat: 115.8 g. (14% of total wet weight) Average weight of edible meat: 108.2 g (11% of total wet weight)

Step 3: Assuming a meat-shell ratio in a Clambush #1 T. crocea that is similar to that in a Saipanese T. gigas, then we can derive the following averages for Clambush #1:

Average total wet weight: 357.6 g Average dry shell weight: 350.6 g Average weight of meat: 50.1 g. Average weight of edible meat: 39.3 g

Step 4: The seventeen clams in Clambush #1 thus should have collectively weighed about 6.079 kilograms.

Step 5: One kilogram equals 2.2046 pounds.

Step 6: It follows that the clams in Clambush #1 should have weighed about 13.4 pounds, which should not have been beyond the capacity of an individual to carry, assuming he or she had something to carry the clams in.

Step 7: We can also calculate that the total weight of edible meat procured by transporting Clambush #1 to the Seven Site was about 668.1 grams or about 1.5 pounds. A reasonably substantial meal for one person or even two people. It may also well be that the shell/meat ratio is higher in the large, thick-shelled T. gigas than in the smaller T. crocea, which would mean that the total edible meat weight of Clambush #1 would be greater and the total wet weight of the clambush would also increase. If we double the estimated edible meat weight to three pounds (which seems liberal), this would increase the total clambush weight to about fifteen pounds, still easily within the range of what an individual could carry if he or she had a container in which to carry it.