Article

Not here yet, but knocking on the door...?

Not here yet, but knocking on the door...?

Can you imagine the response if you asked an Islander whether we were in need of another source of red water in our rivers and streams? There is an invasive aquatic species that could be just that. And yet, at first glance, the Chinese mitten crab (Eriocheir sinensis) looks quite harmless, even has that “cute” factor – with those fluffy, furry wrist-bands on its long, rather sharp and lovely white claws. Don’t be fooled! It has the potential to wreak havoc on not one but two aquatic ecosystems – our freshwater rivers and saltwater estuaries.

This crab hasn’t arrived on PEI – yet. It has, however, made appearances in the Great Lakes and looks to be working its way closer to marine waters in the Gulf of St. Lawrence. As a catadromous species, it needs both salt and freshwater to complete its life cycle, so although it’s been present in the Great Lakes since 1965 it has not been able to establish. BUT in 2004 it was found near Quebec City which for a mitten crab that can travel several hundred kilometers is just a hop, skip and jump from the saltwater it needs to rear larvae. There is also a population now in the Hudson River in New York.

And so what’s the harm these little guys can do? Well, like all invasive species, they’re opportunists – the kind of uninvited guest that takes over and trashes the place. For an island province with a long-standing problem of easily erodible soils, the most worrying potential impact is this crab’s habit of building bank burrows – observed at densities as high as 30 per square meter – along estuaries and rivers. If the crab were to get established on the Island, burrows at that frequency would destabilize our soils and put them further at risk of erosion from bank collapse during high flow events or high tides.

These are also walking crabs quite adept at moving around obstacles like dams or nets and traveling hundreds of kilometers up river. In Germany where they’ve become more than a nuisance, their migrations en masse foul fishing gear, block fish ladders, sluices and other in-stream structures. They are aggressive predators and not particularly picky, eating aquatic plants, invertebrates and small fish.

So, if you fish with nets or otherwise spend time in estuaries and rivers around the Island, please keep a watchful eye out for the crab with mittens. Let the PEIISC know if you do find one, so that we can respond quickly and hopefully keep it from establishing itself here on PEI.

- Megan Harris, PEIISC Member and West River Watershed Coordinator

Mitten crab bank burrows Photo from www.dfg.ca.gov – the California Department of Fish and Wildlife
Mitten crab bank burrows Photo from www.dfg.ca.gov – the California Department of Fish and Wildlife
Mitten crab (Eriocheir sinensis) Photo from www.zoopicture.ru
Mitten crab (Eriocheir sinensis) Photo from www.zoopicture.ru