Stormy Margate

Stormy Margate

Saturday, 8 January 2011

Winter Crab deaths - the statistics and a ramble

On the front page of the Isle of Thanet Gazette (07/01/11) there is a article on the recent deaths of the Velvet Swimmer crabs, in the article are the statistics released by the Thanet Coast project. In total the Thanet Coast project wardens accounted for 20,000 + dead crabs. Working around the coast in order working from the west to the east the stats are 4,500 by Nayland rock Margate, 10,000 at Palm Bay, 4,000 at Kingsgate, Broadstairs and 1,500 at Ramsgate main sands. Other bays like Epple, Walpole, Botany and Joss are not included in the count.
I suppose looking at the statistics, if this had been a earthquake Palm Bay would had been the epicenter. However, for us beachcombers dead velvet swimmer crabs in the winter have been a common site since the mid seventies. The only surprise is the numbers that have come ashore, so why is this ?
There are many reasons and I suppose the only explanation that I maybe can explain through experience is the fact that perhaps when the crabs are weakened by the first stages of hypothermia they are easy prey for predators. In this case the primary inshore predator would have been Cod and I can recall as a fisherman in the early eighties when gutting large winter Cod caught off the Palm Bay area the stomachs were full of crab including velvet swimmer crabs. In recent years the inshore stocks of large Cod have dwindled and supposing that the large Cod numbers would had been at the 1980's levels during the recent drop in water temperature would as many dead crabs had been washed ashore ?
On a another point there was a size difference in the dead crabs (1500+), those found at Ramsgate as they were mostly small crabs with very few measuring more than 60mm across the carapace, looking at the photographs taken at Palm Bay the dead crabs found there were mostly large adults. As a coastal warden for Ramsgate main sands and western undercliff I surveyed the area well during the summer. It was noticable around the East Pier wall and the breakwater rocks on the East Pier entrance that there were a few small swimmer crabs swimming around the breakwater rocks and up the sea wall when the tide was up .The strange thing was that during the summer on the western undercliff and western breakwater rocks there were none and this did reflect in my survey of the dead crabs.
Ramsgate is on the edge of the chalk reef and when the wind does have a touch of North or East behind it, the tide does neatly deposit items near the East Pier from the edge of the chalk reef as my surveys and photographs have proved.

Living in Margate most of my life I am familiar with everything on the chalk reef and as I am living and beachcombing closer to the edge of the reef it is opening my beachcombing to a lot more diversity. This is because any wind with a touch of west behind it comes straight off the Goodwins, Downs and Sandwich Bay. So when the wind is back into the west I will back on the trail of the Chinese Mitten Crab, counting lesser spotted dogfish and thornback ray egg sacs, monitoring sea coal, counting small scallop shells, collecting European cowries, collecting amber and counting sea birds etc.., great days ahead.

2 comments:

Tony2 said...

Just come back from survey of my bay Westbrook Bay to St Mildreds which featured the main bulk of crabs found dead last year and the year before. This year there were nowhere near as many and mainly juvenile crabs 60mm. We are now just left with shells, arms and legs.
Normally during the summer when on Seashore Safaris with the children we find at least about 5 Velvet Swimming crabs on each trip. This year despite running more Safaris around the Thanet Coast we only found 3 during the whole Summer. The fact that the mortalities discovered this year were further round the coast could indicate the edge of their existance is moving back along the coast due to the colder winters experienced over the last 3 years.
We can only theory I suspect that we will never find the definite reasons. Keep up the good work.

Tony Beachcomber said...

Tony

Last year when the Walpole Bay pool was drained out I did notice many swimmer crabs under the ledges and in the cracks in the steps at the back of the pool. Obviously the survivors from previous winter. If the pool is to be drained out this spring maybe it would be worth noting how many survivors there are in residence.