'PHOTOGRAPHY' AS A USEFUL METHOD FOR ESTIMATING THE DENSITY, SEX-RATIO AND BODY SIZE OF THE SURFACE-ACTIVE AUSTRUCA PERPLEXA (H. MILNE EDWARDS, 1852) (BRACHYURA, OCYPODIDAE)

Estimations of crab density, sex-ratio, and body sizes are difficult. Though the 'burrow excavation' method is widely used to estimate these parameters in surface-active crabs, it is destructive to crab populations. Therefore, an alternative, non-destructive method is desirable. This study compared the non-destructive 'photography' method with the 'burrow excavation' method in a fiddler crab (Austruca perplexa (H. Milne Edwards, 1852)) population. Twenty 0.25 m2 quadrats were set out and 4 photos were taken of the surface-active crabs in each quadrat. All crab burrows were then excavated, and the crabs were collected to estimate their numbers, sexes, and body and claw sizes. Afterward, the photographs were analysed to estimate the same parameters by using the GIMP program. These parameters were then compared between the two methods. The results showed that these parameters were not different between the methods compared. This study thus reveals that the 'photography' method could safely be used instead of the 'burrow excavation' method, and yield the same results.

Automated summary

This study compared the non-destructive 'photography' method with the 'burrow excavation' method in estimating crab density, sex-ratio, and body sizes in a fiddler crab population. The results showed that there were no differences in the parameters estimated between the two methods. This suggests that the 'photography' method could be a suitable alternative to the 'burrow excavation' method.