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

Published online by Cambridge University Press:  19 September 2003

Joana M. Jordão  and
Rui F. Oliveira
Joana M. Jordão
Affiliation:
ISPA, Unidade de Investigação em Eco-Etologia, R. Jardim do Tabaco, 34, 1149-041 Lisboa, Portugal, E-mail: [email protected] and [email protected]
Rui F. Oliveira
Affiliation:
ISPA, Unidade de Investigação em Eco-Etologia, R. Jardim do Tabaco, 34, 1149-041 Lisboa, Portugal, E-mail: [email protected] and [email protected]
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Abstract

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 significantly different from population density estimated by excavation, but the population density estimated with visual counts was significantly lower than the absolute density. Ovigerous females should be the main cause of these differences because they frequently remain underground, but other groups of crabs are also contributing to this difference. Burrow counting is an accurate and quick non-invasive method for the census of U. tangeri. Other population measures (e.g. sex ratio) are not obtainable by burrow counting 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.

Type
Research Article
Information
Journal of the Marine Biological Association of the United Kingdom , Volume 83 , Issue 5 , October 2003 , pp. 981 - 982
Copyright
Copyright © Marine Biological Association of the United Kingdom 2003

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