Monthly Meeting – March

March 13th, 2011

Sea Cucumbers in the Indian Ocean – Mandy Knott

March’s meeting was a talk by Mandy based on her work with Shoals Rodrigues (http://www.shoalsrodrigues.net/), surveying sea cucumbers in the lagoon of the island of Rodrigues.

Rodrigues is the furthest east of the three Islands of Mauritius and, from a marine biology view, is interesting because it is effectively isolated from lands to the west by the trade winds and ocean currents that sweep in from the south east, from which direction the nearest landfall is Australia. Politcally it is an autonomous region of Mauritius. Much of the land is mountainous and many people turn to the sea to provide their living. To this end Rodrigues does possess the largest coral lagoon in the world.

There’s always a ‘but’ and for Rodrigues there are several when it comes to taking advantage of this resource. What all the ‘buts’ come back to is overfishing; the large predatory fish have all gone from the lagoon, the fishermen have no boats capable of fishing beyond the safety of the lagoon, and the sea cucumber has become the main stay of the fishery.

Sea cucumbers are not vegetables, or even plants, but animals – Echinoderms – closely related to urchins and starfish. Their basic form is a sausage shaped animal with a mouth at one end that has tentacles that pass food to the mouth. Food for these animals usually being detritus or some other microscopic source or protein. Reproduction can be sexual or asexual – either male and female animals communicate by and respond to chemical signals in the water to synchronise the release of sperm and eggs into the water, or some species can also multiply by splitting into two parts. Overfishing therefore can be a big problem for sexual reproduction in these animals – as they need to be close enough to one another in order to be able to use their chemical communications effectively; the population could drop to a point where the animals are present but unable to breed.

That they could be thought of as food may seem an unlikely direction, as to western eyes they don’t appear all that apetising and the processing they go through after being caught doesn’t improve this viewpoint at all. However sea cucumbers are valued in China and South East Asia for both cuisine and traditional medicine – the general rule being the uglier the better.

Signs that the sea cucumbers were following the fish have been there for some years, and four reserves were set up around the lagoon to give areas where there was no fishing. Unfortunately it seems these are not being managed or enforced. An earlier Shoals Rodrigues survey had estimated the sea cucumber population of the lagoon at @48 million. The 2010 survey looked at many of the same sites and used the same statistical model to estimate the population again – and found a significant reduction in the overall population.

Prior to restrictions of fishing being imposed a official study found that 55000 animals were taken in 15 days (these were just the fishermen they knew about – there were probably more people fishing unregistered).

One glimmer of light on the horizon is the possibility of ‘ranching’ sea cucmbers. This would be a bit like farming them. Even this has its problems though; the Rodrigues government is understandably very keen to to get it going and wants use a species – Holothuria Scabra – that is native to Mauritius and has been successfully ranched elsewhere. One of the key criteria is that the species used should be one that is native to the Rodrigues lagoon and Holothuria Scabra has only ever been recorded on one survey there – one commissioned by the government; it has never been recorded by any of the other surveys, which have taken many days and many sites into account. Naturally there is some scepticism about that one survey and some concern of the effects the introduction of a non-native species could have on the endemic species resident in the lagoon.

Another glimmer is that a fisherman’s cooperative has been set up and is in the process of obtaining and fitting out boats fishing beyond the reef, which would hopefully reduce pressure on the lagoon species. To what degree that is successful remains to be seen.

See also –

http://www.sos.bangor.ac.uk/research/php/theme.php?project=445 for some information on Bangor University’s work in Rodrigues

http://www.sempa-rodrigues.com/images/3rd%20Ecology%20and%20GIS%20Interim%20Report.pdf – a report on SEMPA (the South East Marine Protected Area) including survey data

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