Invasive Non-Native Species Are All Around


Chris Packham explains the destructive impact of the American Signal Crayfish, an invasive non-native species (see also below)

David Pottinger writes:

David Buckler, a Committee Member of Fleet Pond Society, recently brought the above video on the American Crayfish to our attention. It’s well worth watching and quite shocking in it’s way. It gives a clear example of the undesirable and major consequences that an invasive alien species can produce if unchecked.

Colin Gray has previously given an overview of invasive species at Fleet Pond, see the article Aliens At The Pond. Here’s some additional information.

In late February Rachel Jones, the Hart Ranger, attended a talk by Glen Skelton of the Surrey Wildlife Trust on invasive species (held at the Basingstoke Canal Visitors Center). Here are some extracts from Rachel’s notes from the talk:

The presentation looked at each invasive species found in the catchment areas and what action was taking place to minimise the threats. Fleet Pond unfortunately has quite a few of the aliens, as do a few other sites that Hart manages.

The main ones that are of interest to Fleet Pond were:

  • New Zealand Pigmy Weed (Crassula helmsii): There are significant areas of it in the Canal not far from the Pond so perhaps this is where it came from. It is troublesome to reduce it.
  • American Crayfish (Pacifastacus leniusculus): Parts of the River Wey are swarming with these, apparently they eat all the invertebrates and aquatic plants. They also destabilize banks as they burrow holes into the river/stream banks adding to siltation and erosion. The extent of the crayfish population at Fleet Pond is uncertain but it’s a species we must look at given that we want to increase our invertebrate and plant life.
  • American Skunk Cabbage: Even though it is not as widespread as Balsam for example, it is still a challenge to get rid of.
  • Orange Balsam: We are familiar with the Himalayan Balsam that we have in (currently) small amounts in the Brookly area (it is also on some of the other Hart sites). But we need to keep an eye on the Orange Balsam as it is creeping in as well.

Over all, it seems as though there is still no one way of reducing or eradicating these invasive species. Much research is taking place to help get on top of them but this all takes time, particularly with biological control methods.

Others mentioned in the talk & which are a problem in the nearby countryside include:

  • Japanese Knotweed
  • Giant Hogweed
  • Floating Pennywort (River Wey)
  • Water Fern (Farnham Park ponds)
  • Parrots Feather (Church Crookham canal)
  • Quagga Mussel
  • Killer Shrimp.

There is a free home course that is available if anyone would like to help us spot these threats at the Pond, or other sites that link to us or are close by. See:

Finally, the destructive impact of the American Mink (Neovison vison) at the Pond should also be noted.

From the SWT site (see here):


“The American mink is a semi aquatic species of mustelid which is native to North America. It first became established in the UK in the 1950s when animals escaped or were released from fur farms. American mink have adapted well to the UK and are now common and widespread throughout Sussex.

They are one of the few animals which can follow native wetland species such as the kingfisher and the water vole into their burrows and nests, and in some cases they have had a devastating impact on population numbers of these species.”

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