Land Crab Monitoring Update 2024

14 June 2024

Conservation

Ascension’s native land crab (Johngarthia lagostoma) completes its annual migration down from Green Mountain to the coastline to spawn from January to May.  

This year, the Ascension Island Government Conservation and Fisheries team conducted a 10-year population census, counting females using North East Bay to release their eggs. A total of 10,565 females were recorded, a rise in numbers from the 8,124 counted during the 2013 census. Further analysis of these figures will give an overall number (including the nights not counted) which is expected to show a significant rise in the female population.

Each female land crab is counted every 15 minutes on a pre-determined transect (stretch of the beach) during a 3-hour timeframe. She is marked with a non-invasive blue line on her shell to note that she has been counted and will not be again during the survey. These transects are walked over alternate evenings during a 7-day spawning period. Land crabs are very particular about when they choose to lay their eggs, each month they start their spawning 10 days after the full moon. 

This species of land crab is only found in 4 small islands around the world. Very little is known about this endangered crab so the data collected from the surveys will ensure the future of this rare and intriguing animal.