Suchergebnisse

Context
Rat (Rattus spp.) eradication operations in the tropics are often put at risk by the presence of land crabs, in particular hermit crabs (Coenobitidae), which consume toxic bait and thereby render it unavailable to rats.

Aims
We estimated hermit-crab densities in areas of high abundance, assessed crab bait consumption rates and determined the required baiting application rate to ensure that 100% of Pacific rats (Rattus exulans) consumed bait in areas with high crab densities on Henderson Island, South Pacific.

Methods
Crab densities and rat densities were estimated through Distance sampling of crabs and mark–recapture of rats. Non-toxic rhodamine-dyed cereal bait pellets were spread by hand at varying densities within four study plots and rats were captured 12 days later and examined for the presence of rhodamine biomarker dye.

Key results
Crab densities (primarily Coenobita perlatus) varied between beaches from 130 crabs ha–1 to 1370 crabs ha–1, with rats occurring at respective densities of 28 and 7 rats ha–1 on these beaches. Estimated bait consumption rate of C. perlatus was 3.8 g crab–1 day–1. In total, 100% of rats were positive for rhodamine-dyed bait, despite the high densities of crabs present.

Conclusions
The results support the prospects for a successful rat eradication on Henderson Island, although careful consideration must be given to the potential impact of an eradication on non-target species. The estimated bait consumption rate by C. perlatus found in the present study may allow other eradication operations to make initial calculations of the required baiting densities to overcome interference from this species.

Context
Cereal pellets containing the anti-coagulant poison brodifacoum at 20 ppm are routinely used to rid islands of invasive rodents. The impact, if any, of the poison on invertebrates is not well understood. This is problematic because many of the islands targeted for treatment harbour endemic invertebrate species, including snails where available information about brodifacoum impact is equivocal.


Aims
Combining field tests and subsequent laboratory analysis, the present study investigated the effect of brodifacoum on the snails of Henderson Island, South Pacific.


Methods
In the field, we housed snails in plastic boxes for up to 10 days to compare the survival of those kept with and without access to brodifacoum cereal pellets. Subsequently, we analysed brodifacoum levels in those kept with access to poisoned pellets, according to whether they survived or died.


Key results
There were no detectable differences in the survival between the captive snails kept with and those kept without access to brodifacoum. Among those with access, there were no significant differences in brodifacoum concentrations between the minority that died and the majority that survived. In fact, brodifacoum was detected in only a few samples.


Conclusions
Brodifacoum appears not to pose a risk to the snails of Henderson Island.


Implications
Although it would be prudent to test the impact of brodifacoum on the resident snails before proceeding with a rodent eradication on other islands, we suspect the Henderson results can be extended to other sites.