Comparison of non-invasive methods for quantifying population density of the fiddler crab Uca tangeri

Jordão, Joana; Oliveira, Rui Filipe

http://hdl.handle.net/10400.12/1317

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Authors

Jordão, Joana

Oliveira, Rui Filipe

Abstract(s)

Excavation counts (absolute density), burrow counts and surface active individuals visual counts in a Uca tangeri population were compared. Population density estimated from burrow counts was not signi¢cantly di¡erent from population density estimated by excavation, but the population density estimated with visual counts was signi¢cantly lower than the absolute density. Ovigerous females should be the main cause of these di¡erences because they frequently remain underground, but other groups of crabs are also contributing to this di¡erence. Burrow counting is an accurate and quick non-invasive method for the census of U. tangeri.Other populationmeasures (e.g. sex ratio) are not obtainable by burrowcounting and only further understanding of the activity patterns of this species along the tide cycle, moon phase and reproductive season will allow visual counting of surface active individuals to be used as quick, efficient and non-invasive method for crab density and population structure estimation.