Alien species or non-native invasive species
This is one of the biggest threats facing the UK environment after climate change. The “Alien” or non-native species are not a part of the natural environment in the UK and the native species are not adapted to existing with them. The aliens have different ways of impacting, such as bringing and spreading disease, predation, and habitat modification.
The Ribble has several confirmed alien species. These are:
American Mink (Mustela vison) (for more info click link)
The American mink was brought to Britain for fur farming. There have been many escapees as well as deliberate releases by animal rights activists.
The Mink are voracious predators, preying on fish, mammals and birds. They will take large salmon many times there own size. They also are responsible for the massive decline in the population of water voles as they are small enough to enter the voles burrows.
Desciption:
• Mink males are up to 60 cm long (42cm Body and 18cm tail) females are slightly smaller at 51 cm long (36 cm body and 15 cm tail).
• They are glossy dark brown, looking black in certain light. However due to farming history there are some of lighter colour and/or patchy.
• They are accomplished swimmers and are often seen in the water, and mistaken for otters.
Control:
• It is important to undertake surveys to assess the density and size of the Mink population within a catchment
• The survey can then be used to set up a trapping strategy, which can be targeted and adapted where necessary.
• Encourage the Return of the European otter, as it is believed there presence will reduce the presence of mink in an area (however it will not necessarily guarantee it as there habitat requirements are slightly different)
Red Clawed American Signal Crayfish (Pacifasticus leniusculus) for more info click link
The American signal Crayfish were brought to the UK for aqua culture and have escaped or been introduced into rivers and streams as a food source. They are carriers of Crayfish disease which is deadly for the native white claw crayfish and has caused a serious decline in numbers. They also compete for habitat with the natives. They eat nearly all aquatic animals including fish and fish eggs. Work by the Ribble Catchment Conservation Trust has shown the serious impact signals have on fish populations. Their burrows in river banks also lead to greater erosion and thus sediment pollution
Description:
Altough the main identification factor is the large red claws, these are not always obvious on juveniles. They are capable of regrowing any limb, which they can “discard” if threatened or attacked.
Control:
Trapping has in fact been shown in some cases to make the dispersal worse, due to the reduced cannibalism. It is for this reason that trapping should only be done under licence from the Environment Agency and by an expert. Even the most intensive trapping has not successfully reduced their populations.
Canadian Pond Weed (Elodea canadenis)
Canadian pond weed was introduced into UK in the 19th century for ornamental ponds. It is often sold as an oxygenating plant. However at night it uses large quantities of oxygen that may suffocate other aquatic animals. It also traps sediment and detritus such as leaf litter choking water ways. It can grow from small roots. The dense blankets it grows into also out compete native plants and act as a barrier to migration. The Ribble Catchment Conservation Trust has undertaken a scheme to increase flow on stock beck which has removed large quantaties of Canadian pond weed which favours slow or still waters.
Control:
There are various forms of control, such as mechanical cutting, herbicide and increasing river flow. However these must be done by an expert and as part of a program of several years as it is able to re-grow very rapidly and from small stems not removed.
Himalayan Balsam (Impatiens glandulifera)
Introduced to the UK in the mid 19th century as a garden plant this annual plant has spread rapidly. It has achieved this due to projecting it’s seeds up to 4 metres from “explosive” seed pods. The plant can grow to 2 metres in height and very dense, out competing other bankside vegetation, decreasing biodiversity. When the plant dies in the autumn this causes the banks to be bare and easily eroded. This adds to sediment pollution.
Control:
Himalayan Balsam is very difficult to control, it can be done by pulling or cutting, and herbicide. However this is best done in the spring before it has a chance to reach full height. It needs a “top down approach”, starting at the top of a catchment moving downstream, or it will easily recolonise.
Japanese Knotweed (Fallopia japonica syn. Polygonum cuspidatum)
Probably the most common and recognized invasive species. It is present through out Britain. It causes severe structure damage to roads and buildings, but also erodes river banks and out competes native plants by shading them out. It can grow in excess of 3 metres tall and regenerates from root fragments as small as 2mm.
Control:
Due to it’s hardyness and ability to regenerate it is a difficult plant to eradicate. There are a few options that require professionals. Herbicide (either spray or stem injection) can be used. Digging and removing all soil from a site, dumping in a registered land fill, or burying it over 5 metres deep. The burial can also take place using “cells” however the digging options aren’t suitable for rivers.
Alien invasives What can you do?
Don’t introduce any!! Prevention is always the best solution. There are more invasive’s out there that the Ribble hasn’t got, so don’t bring any in. And please don’t add any more of what’s already here either! Canadian pond weed is often sold in garden centres, when it is planted in ponds and takes over, you will need to remove it, Dispose of it properly and carefully. Crayfish can be bought in pet shops, when they get to big for your tank don’t flush them down the toilet or release them into the wild!
You could always volunteer and help on work days (Please add link to volunteer page) or why not support the trust by becoming a member (Please add link to support the trust page)
Commercial Fisheries
Over fishing by commercial trawlers and netsmen as well as inappropriate methods can have a negative affect on not just the sea, but all the animals that benefit from the sea, including fish and birds. Over fishing, i.e. not leaving sufficient fish to repopulate, results in not only that fishes decline, but all the other fish linked to it. For example loss of sand eels (used for animal feed and in some parts of the world, fuel for Power Plants!) Results not only in decreased sand eels, but sea trout and puffins as sand eels are a major part of their diet. Over fishing of Cod, may mean that in the not to distant future we won’t have any Cod to eat, but juvenile cod make up a part of the Salmons diet.
Inappropriate methods include those which take in by catch, such as fish of other species that are to small or are ready to bread, but it may also include dolphins or birds. Only appropriate methods should be used to halt this from happening. Other inappropriate methods include Scallop dredging. The dredging of the sea floor to recover scallops is like ploughing the sea bed over and over again, until it is barren and nothing will live their. However, not all commercial fishing is bad, sunken long lining for certain fish species is an effective method that only catches the target fish. Hand picked scallops are a more sustainable and low impact way of gathering scallops.
What can you do?
Make sure that you only eat sustainably caught fish. To see a guide to fish to eat or avoid click here for a copy of the MCS Pocket good fish guide. (Please add link to adobe file for MCS pocket good fish guide)