The Spider Crab - Is it an Invasion, or
just a Seasonal Bounty?
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'.
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 - Balanusbalanoides. (photo Rod Attrill)
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 Maiasquinado. 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.
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!
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.
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.
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.
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.
