Saturday, May 02, 2020

'Last to Sea' #3 - Horseshoe Crab

Work continues on this year's contribution to the Elora Sculpture Project : 'Last to Sea'

Overall installation rough
c) Horseshoe Crabs - formed from several pieces, with a long forged tail (about 2 feet total). Unchanged 450 million years, through 5 Extinction Events (!!).

Once I started doing background research towards selecting the individual species, the situation of this individual animal was the most shocking to me. Often described as a 'living fossil', horseshoe crabs have managed to survive through FIVE previous mass extinctions. The blood of these animals is a copper based blue - not the iron based red of almost all other creatures on earth.


In modern times there are four main species of horseshoe crabs. The well known Atlantic type is still plentiful, if under stress. The human impact here is primarily due to destruction of habitat. The beaches needed for spawning are increasingly built over by humans wanting holiday homes.

Chinese Police officer - rescue of Chinese Horseshoe Crabs at an illegal blood harvest operation.
The Chinese Horseshoe Crab is both the physically largest - and the one closest to complete extinction. Like many other 'strange' animals, traditional Chinese medicine has considered horseshoe crabs of value, but certainly centuries of this use has not seriously impacted natural populations. The problem started in the 1950's, when it was discovered that an element in that blue blood strongly reacted to bacterial contamination, becoming an increasingly valuable medical test. (1)

Harvesting the blue blood of the horseshoe crab (Image: Alamy)
" There were 600,000-700,000 breeding pairs on the Guangxi (China) coast prior to the 1990s,... By 2010, there were only 300,000. ... Based on (Guangxi Ocean Institute) research, the institute estimates the current population of Chinese horseshoes in Guangxi to be only 40,000 breeding pairs.
Huang Nie of the Guangxi fisheries authority says these regulations limit the catch of wild horseshoe crabs in the region to 20,000 pairs a year. ... Once the blood has been harvested, the horseshoes are kept in captivity to recuperate and then returned to the wild. " (2)

40,000 remaining pairs
20,000 per year have 20% of their blood drained, then 'returned'.

Do. The. Math.

Chinese Horseshoe Crabs can grow to 80 cm total length. They reach adult (breeding) stage after about 9 years, and can live to 20 years old. The average found today is closer to 67 cm, with bodies 34 cm wide and tails making up 34 cm (so roughly half). Females are considerably larger than males. Males can be distinguished by having a three lobed curve to the head of the shell, females an even curved shape. Females have three pairs of spikes on the rear segment, males have six per side.

(Frequent readers will see some repetition of the steps used for 'Abalone') 

Shell plates rough torch cut
My interpretation had its size limited by the scrap steel plate I had on hand (at 22 cm wide).

'Abdominal' plate - contours ground smooth and lower spikes cut in
Once the plates were separated, the outer edges where ground smooth. This mostly done using a bench grinder, with the smaller and tighter edges using an angle grinder. The spikes were cut in using a zip disk, also on the angle grinder.

Heating the head plate - part way through the dishing process
Another limitation to this process was the interior size of my two burner gas forge. The maximum width there is 10 inches, you can see that the 'head' plate only just fits. (This important because of the fragile nature of the K-Wool insulation.)
Once again, the flat plates were dished using a crowning hammer into a dishing form.

Finished forging of the plates
The final shaping of the body plates included working both sides. As well as dishing, contours were formed using a cross peen into a slotted bottom tool. Creases in the head plate were created by hammering back against the edge of the anvil.

Closeup showing tail profiling and bottom tool used
The cross section of actual horseshoe crab tails is triangular, with the flat side downwards. To suggest this profile, I forced a previously pointed length of square stock into a triangular notched bottom tool. The end result was actually a more complex shape than for the actual animal. Forging this element actually took me longer than to shape the two body plates.

 The completed sculpture has slightly distorted proportions from the living animals. The body with is 26 cm wide, the body length somewhat stretched to 36 cm. This mostly because of a larger abdominal segment. The tail is considerably longer in proportion, at 43 cm, bringing the total length to 79 cm.
Again, the whole is left with the 'fire scale from the forge surface', which will rust on exposure to the weather.

Next up : Sea Turtle Shell

Note: There are links for two versions of the source article listed below. The text on both is identical, but the images used differ.

1)Processed into LAL, reported cost is US $60,000 per gallon
2) Taken from the article :
After 450 million years, the Chinese horseshoe crab is now endangered 
Zhong Jianshan : September 30, 2019

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February 15 - May 15, 2012 : Supported by a Crafts Projects - Creation and Development Grant

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