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The Spider Crab - Is it an
Invasion, or just a Seasonal Bounty?
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Recently the television crew from BBC Wales was in both New Quay and Aberaeron to report on a supposed 'invasion' of Spider
Crabs into the shallow waters of Cardigan Bay. They spoke to local
fisherman David Winston Evans in New Quay and Fishmonger Will Willis in
Aberaeron (see the Seafood of Cardigan Bay).
Mr. Evans spoke of his annoyance of the fact
that the Spider crabs can reach the bait in his Lobster pots with their long
claws and it was noted that 'lobsters were being frightened away from the
Lobster pots'.
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Often the Spider
crabs form large mounds containing hundreds or even thousands of
crabs, with females on the inside. This is thought to be a
method of protection against predators especially after moulting when
the shells are still soft. This crab's carapace and legs are colonised by Acorn
Barnacles - Balanus balanoides. (photo Rod Attrill) |
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Tourists to the area however, are unlikely to
ever see a Spider Crab except in the fishmongers or in a Restaurant.
Although the crabs come into shallower waters in the summer months, they are
not found in the intertidal zone or on the beaches.
The Common Spider Crab is know scientifically
as Maia squinado. Its range extends from France
and Spain where it is commonly harvested, up as far as the west coast
of Wales - close to its northern limit.
Spider Crabs live in deeper water in the
winter - in depths of up to 120 metres, but come closer inshore in the early
summer months as water temperatures increase. There is no doubt that such a
migration would tend to result in a greater population density closer to the
shore in the summer. Winston Evans, New Quay fisherman, says they are
present in numbers from about the middle of May for some three months.
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The
succulent leg and claw meat of the Spider Crab is prized on the continent
and is now served in local restaurants as the crabs have increased in
numbers.
Hugh
Fearnley-Whittingstall writes in the 'River Cottage Cook Book':
'The meat is sweet and beautifully textured, which is why the Spanish, who
appreciate such things, will pay more for a large Spider Crab than for a
Lobster of the same weight. I am a total convert, and rate them as even
better than Brown Crabs.' There is a recipe for Spider or Brown Crab
Linguine on Page 336 of his cook book. However, removal of the meat can be a
tedious process!
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Like other crabs, the females carry the
eggs - up to 150,000 , around with them under their abdomen which is
tucked underneath the carapace or shell. Most females are 'berried' or
carrying eggs by May. The eggs take from 60 -75 days to mature at which time
a tiny larva hatches out and swims up into the plankton.
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The reason that
crabs and other marine animals with planktonic larvae lay so many eggs is
that there is a greater chance of wider distribution of the species. This
leads not only to improved territorial coverage but to greater mixing
of the gene pool within the species. The down side of this is that the vast majority of
planktonic larvae become food for other animals - both
planktonic predators and filter feeders on the sea floor. In the tropics,
coral reefs feed mainly on plankton. |
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The larvae are firstly known
as Zoea (see drawing above). they later become somewhat more
crablike in the Megalopa form (see drawing on right).
Altogether, they spend some three weeks floating
about in the plankton at the mercy of the ocean currents until they change
into small crabs and begin life on the sea floor. If they survive their
first year, they will grow to a carapace or shell width of seven cms in that time.
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There is much speculation as to why the crabs
are being found in such large numbers this year. It is well known that Spider
crab numbers can fluctuate wildly from year to year, and this could well be
part of a cyclical population trend. However, Dr. John Fish of Aberystwyth
University is quoted in the Times as saying: 'I have seen
more Spider Crabs on the beaches of Cardiganshire this year than in other
years'. Keith Stone, North Wales Sea Fisheries Officer, said 'It is
rare to find them so far north. It could be because of global warming, ocean
currents or changing migration patterns or they could be adapting to colder
water conditions'.
There is also the possibility that fishing practices
have resulted in a change of population numbers in the other large
crustaceans that might compete with the Spider Crab.
Whatever the reason, the Spider Crab
represents a bountiful natural resource that is more likely to grace the
plates of local restaurants in years to come.
İRod Attrill,
2003
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