Mouse Feasts On Whitebait Caviar

17 November 2004

Mouse Feasts On Whitebait Caviar

It may be an ordinary field mouse, but it’s got gourmet tastes and that’s not a good thing. The common mouse, Mus musculus, has been unmasked as a predator of whitebait eggs.

For the past two whitebait seasons, NIWA scientists have been using video cameras in an attempt to determine what is preying on the eggs of the most common whitebait species, inanga (Galaxias maculatus).

Previous studies have estimated that up to 80% of the eggs are removed from intertidal vegetation between the time they are laid and the time they are washed out to sea (roughly one lunar month).
“Last year, an intertidal mud crab ate all the eggs at one of the two sites we studied,” says Dr Cindy Baker of NIWA. This year, two more sites were monitored. “Mice have not previously been considered a threat to native freshwater fauna, so it was a bit of a surprise to see this small furry creature on the video. The mouse found both sites and devoured all the eggs. After that, it returned to the area repeatedly and continued eating all the eggs each time the site was restocked,” says Dr Baker.

“It’s too soon to say whether field mice are a major predator of inanga eggs. The four sites we’ve studied over the past two years cover only a small fraction of the total spawning ground,” Dr Baker says. The video monitoring will continue next season with funding from the Foundation for Research, Science & Technology.

The research is outlined in the latest update from the National Centre for Aquatic Biodiversity & Biosecurity, which can be found at www.niwa.co.nz/ncabb

ENDS

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