Tuesday, June 17, 2008

Crabs on Roney Beach

In 2005 I wrote a scientific paper about the spider crab Maja squinado for the Irish Naturalist's Journal - my first journal paper in 18 years. The INJ don't publish abstracts or full papers on-line, but the title and volume details are listed in the Archive section of their website.

The scientific citation for the paper is as follows:

O'Loughlin, E.F.M. (2005).
A note on aggregation behaviour and mass mortality of the spider crab Maja squinado (Herbst) (Decapoda, Majidae) in shallow water on the north Co Wexford coast.
Irish Naturalist’s Journal, Issue 28 (2)

The paper is about an unusual event on Roney Beach which I discovered. Selected extracts from the paper:

On 1 August 2004, a large aggregation of thousands of spider crabs was observed on the north Wexford coast in Roney Bay (T212505) near Cahore Point.
Observations were made in very shallow water (1.5 m to 4 m depth) by the author while snorkelling between 2 m and 40 m distance from the shore. Sea conditions were very calm in this locality on 1 August 2004.
On 2 August 2004, sea conditions were rougher as the wind picked up and wave activity increased. This resulted in huge numbers of spider crabs’ carcasses being washed ashore.

I had taken some photographs and included these in the paper submission. However, the Editor declined to publish the photo (it would have cost a lot) and the Editor also felt that the text description was adequate. I include a scaled down version here in this post - click the picture to see a larger version.

It was a fantastic sight that I have not seen in the following years. Apparently it is very unusual, but does happen. In a report in the London Times dated 13th August 1997, an estimated mound of over 50,000 spider crabs, ten animals deep and weighing 10 tonnes, was discovered on the Dorset coast of England at a depth of 4 metres. From the article:

Although there is documentation that spiny crabs come together in this way periodically, no one yet fully knows why or can predict where and when these mass meetings take place." Dr Collins, of the university's Department of Oceanology, estimates that he saw 50,000 crabs, weighing about 10 tonnes. Some scientists believe the mass meetings bring males and females together for mating. But Dr Collins said: "Let's face it, you do not need to get together with thousands of others to mate."


1 comment:

  1. Umagumma, its happened again this week on Old Bawn Strand