Strange beaching due to severe ‘upwelling’


Guy Rogers


HUNDREDS of  mysterious Smith’s swimming crabs , have beached themselves at Cape Recife, apparently trying to escape from severe “upwelling” in the bay.
Algoa Bay is host each summer to classic examples of upwelling, which follows on strong and prolonged onshore winds that fold the waves back upon themselves and draw up icy water from the lower depths, wildlife and environment society conservation officer Morgan Griffiths explained.Reports indicate the crabs have been washing up for over a week on Recife’s beacon beach, which runs along the northern side of the cape. But by Monday, the piles of pink and orange carcasses had grown still further.


A very high tide came up in the early hours of yesterday morning and by mid-morning it had retreated taking most of the crab remains with it.
The birds had torn into the remaining specimens but there were still dozens of claws and shells left behind at the high-water mark.
Libby Sharwood, co-director of the SA Marine Rehabilitation and Education Centre at Cape Centre, said the crabs seemed to be Smith’s swimming crabs as opposed to rock or shore crabs.
“The species have very large nippers and a very distinct flipper-like pair of claws at the back


“We also had an earlier report from a fisherman in a canoe of masses of them shoaling on the surface, off-shore.”


Attempts were made to help some back into the sea but they simply beached themselves again, she said.


“The gulls were dik gevreet and we saw a heron on the rocks that was also presumably eating them.”


Smith’s swimming crabs live out at sea, where they are eaten by tuna. Records note that they were first described by science in False Bay in 1838 but then not seen again until 1978, when enormous numbers appeared.
This sequence happened again in 1983 and 1993.



 

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