Effects of brodifacoum on the land crab of Ascension Island

Published source details Pain D.J., Brooke M. de L., Finnie J.K. & Jackson A. (2000) Effects of brodifacoum on the land crab of Ascension Island. Journal of Wildlife Management, 64, 380-387.
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Summary

Ascension Island and its surrounding islets is considered the most important breeding seabird breeding ground in the tropical Atlantic. However, as a result of human exploitation and introduction of mammalian predators e.g. cats Felis catus and rats Rattus spp., populations of most seabirds, including the endemic Ascension frigatebird Fregata aquila, have undergone large-scale declines. Plans to restore seabird colonies include rat eradication by island-wide application of the anticoagulant rodenticide brodifacoum (successfully applied in other eradications on oceanic islands). Assessment of the feasibility of such a eradication attempt requires evaluation of potential undesired non-target effects. This study investigated the effects of brodifacoum upon the native land crab Gecarcinus lagostoma and the potential for secondary effects upon crab scavengers and predators (including humans).

Land crabs were kept caged in their natural environment on Ascension for varying periods of time. They were fed Talon pellets (20P and 7-20, 0.002% brodifacoum) to simulate maximum exposure should an island-wide rodent eradication programme take place. Body parts were analyzed for brodifacoum residues to assess for potential for secondary poisoning effects upon crab scavengers and predators.

The crabs readily ingested Talon pellets but none appeared to die as a result of exposure to brodifacoum. Upon analysis of body parts, only low concentrations of brodifacoum were found in their bodies (less than or equal to 0.129 active ingredient/g wet body tissue) after exposure. Brodifacoum was not detected within crab claws (which may be eaten by people) at any time. Brodifacoum residues did not appear to persist long-term as no residues were detected in any body tissues 1 month following exposure to the rodenticide.

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