Ascension : Land Crab Monitoring Scheme
Submitted by The Islander (Raymond Ellick) 19.10.2006 (Article Archived on 02.11.2006)

Considered a pest by some, notably gardeners and a delicacy by others the Ascension Island Land Crab (Gecarcinus lagostroma) or to give its correct title (Johngarthia lagostroma) is a fascinating creature.

Prepared by Natasha Williams-Conservation Assistant

Land Crab Monitoring Scheme

Contributed By Pete Ellis- MOD SHEP Adviser (Volunteer)

THE LAND CRABS OF ASCENSION

Considered a pest by some, notably gardeners and a delicacy by others the Ascension Island Land Crab (Gecarcinus lagostroma) or to give its correct title (Johngarthia lagostroma) is a fascinating creature.

As one of the few endemic species found on the Island it has been subjected to numerous research projects and observations. Despite this bombardment of scientific minds much remains undiscovered about the species including breeding behaviour, migration routes and the origin of the species on Ascension. Of the latter it appears possible that even with the complex current patterns around the Island these could facilitate the transportation of crab larvae from the West Coast of Africa. As yet this theory suggested by Ashmole & Ashmole (2000) remains unproven through scientific study.

Land Crab distribution and colouration patterns have been studied in the past but have failed to provide conclusive evidence in support of the data collected. Previous studies have also tended to concentrate on areas with easy human access such as NE Bay where breeding crabs and egg releases were observed. What occurs along the remainder of the coastline which is less human friendly but probably ideal crab country remains a mystery.

For continuity purposes, monitoring of crabs along NE road takes place at least once each week. This involves hand capture of the crab, recording size, sex and position and noting any sign of eggs on female captures. The crabs are then marked, presently with so called indelible ink, but this method is far from ideal and fades quickly due to the damp conditions favoured by the crabs and their habit of squeezing into small holes rubbing off the numbers.

In addition to hand capture trials are taking place using traps and methods used in the fishing industry. Several traps were purchased and baited with road kill Rabbit and Grouper remains after filleting. This mixture of “bait” discovered that Land crabs are partial to Grouper and even remained active during daylight to continue eating. The use of traps or crab pots allowed re-capture of marked crabs, again something not possible with previous studies due to limited resources and the wide dispersion of the marked crabs.  The crab pot trials have been concentrated at three sites in close proximity.   It is anticipated that the relocation of the pots along potential routes at a set distance will produce recapture of marked crabs indicating true migration paths during breeding periods.

Land crab monitoring is a volunteer pastime. The amount of time you spend on the project can be varied to suit differing lifestyles although early morning, night time and after rain observations tend to be the most productive for hand capturing.

Following the initial seven day trial crab pots are set late Friday afternoon. Traps are baited and shaded to prevent any overheating of the crabs. These are then checked the next two mornings for crab activity and recorded as previously described.

There is still so much to discover about the Ascension Land crab and limited resources presently available. Anyone with the enthusiasm to become involved in the project should contact the Conservation Office for more details. 

COMMENCEMENT OF LAND CRAB MONITORING

1. With effect Monday 11^th September 2006, monitoring of the Ascension Island population of Land crab (Gecarcinus lagostoma) commenced. The aim of this continued monitoring is to determine migratory routes of the species and assist with reproductive studies.


2. During the sampling study land crab capturing techniques using baited traps will be utilised. This will enable the monitoring team to size, sex and determine of population distribution using the global positioning system (GPS) across the Island.


3. Traps similar to the photograph at Annex A will be used for the process. These traps will be placed in known areas of land crab activity particularly at locations along the NE and NASA Roads.


4. Assistance from the public is requested to ensure that the traps are left undisturbed during the study period. This is particularly important during nightfall and following periods of rain when land crab activity is most prolific.


5. The study forms part of the continued work by the Conservation Department to monitor wildlife on Ascension Island and will greatly assist our understanding of this endemic species. In this instance the work will be carried out by volunteers working under the guidance and approval of the Conservation Officer.


6.  Information on the voluntary opportunities to assist with this and other wildlife monitoring programs are available from Conservation Department using the contact details above.

Pete Ellis

Land crab Monitoring Team