Environment A to Z of Canal Wildlife
A to Z of Canal Wildlife: P - R

Pondweed

To the casual towpath walker all those numerous ‘weeds’ that grow in our canals are pondweeds, after all the canal is just a long pond, and who has heard of canalweed?! However, the true pondweeds are but a few in the myriad of plants that grow along all of thecanals of Britain. Which grow where, and how abundantly, is determined by many complex conditions, but you would be hard pressed to find a canal that did not contain at least a few of the 21 British pondweeds. Indeed, in some canals the pondweed is so dense that it impedes boats and fouls propellers. The growth of all water-based plants is affected by many factors, not least water quality, depth, and light availability.

The larger plants that grow in fresh water are collectively known as macrophytes and include the well-known reeds, water-lilies and pondweeds, but there are many smaller relatives, some smaller than 1 mm across. Macrophytes also include non-flowering plants like the quillwort.

The Pondweeds, Potamogeton, are a large family and as some tend to hybridise they are difficult to identify. However, among the commonest is the floating, or broad-leaved, pondweed, P .natans. It is easy to identify by its large oval floating leaves,( which often blanket long stretches of canal), together with long, narrow submerged leaves. Other typical members of the family are curled pondweed, P. crispus, which has only wavy-edged submerged leaves and small pondweed, P. berchtoldii which has only grass-like submerged leaves. Macrophytes are a feature of still, shallow water, with the widest selection being found in clear shallow water. The bottom-rooting species, being anchored, can withstand some water flow, but the free-floating species can be washed away. On canals with boating activity, nearly all plant growth is near the water’s edge, any free-floating plants survive, sheltered between their rooted neighbours or in side-ponds where water disturbance is minimised. Powered boats on canals not only physically damage water plants, literally chopping them to pieces, but they also kill plants by stopping light reaching them. The churning propeller stirs up the silt from the bed of the canal, returning it to suspension in the water and making it cloudy so that light cannot penetrate to the plants. The more boats, and the faster they go, the worse the water gets. More and more weed is lost together with all the wildlife that the weed supports.

Balance is the answer. A canal is not a canal without boats. Boaters want to see a healthy waterway full of wildlife, not a sterile, dirty and uninviting water channel. So not too many boats and slow down. The central channel will be kept clear and the weeds will survive along the banks. Wildlife and boats can exist in harmony with just a little consideration.

Rats

Black Rat

There are two species of rats in Britain, the black or ship rat and the brown or common rat. Brown rats were unwittingly introduced into Britain as stowaways aboard the ships of the eighteenth century. Being more aggressive than the black rat that had infested the country since medieval times, the brown rat soon supplanted its meeker relative.

Although not often seen the brown or common rat, Rattus norvegicus, is indeed very common along Britain’s canals and is the one featured here. The shy, nocturnal rat is undoubtedly our most disliked, as well as being our most destructive, mammal. It can be found almost everywhere and is as much at home in the countryside, especially if there are old buildings nearby, as in the cities. A canal, with its associated structures and towpath hedgerow makes an ideal environment for the rat.

This rodent has a heavy 8-inch (20cm) body, with a tail almost as long. Its shaggy coat is greyish-brown above and off-white below. Being omnivorous, it will eat almost anything, alive or dead; it damages and contaminates crop stores and carries disease. This burrowing animal will over-winter anywhere that affords some undisturbed shelter, even rubbish tips, especially if there is a food store close by that they can plunder. This is when they do the most damage, gnawing away at the fabric of buildings in an attempt to reach the farmer’s grain or animal feed store to satisfy their enormous appetites. In early spring, the rural population moves from their winter quarters in out-buildings, sheds, barns, culverts, boatyards and wharves etc. into the hedgerow and along the canal and this is when you may spot one scurrying along the towpath or swimming across the canal. Be careful though, rats and water voles are easily mistaken for each other. Although the rat may live in places we would consider foul and dirty it is itself a very clean animal, taking the greatest care in its personal hygiene.

Rats breed prolifically, reaching a peak in late summer. Four to six litters, usually containing seven blind, deaf and furless young are produced each year. The young grow rapidly, reaching maturity in only four months to become parents themselves. They return in late October and November to their winter quarters.

Despite man’s best efforts, and huge sums of money spent on many campaigns to contain the rat population, there are estimated to be over 60 million rats in Britain. More rats than humans so you must have seen one!

Rushes

Rushes are grass- like plants with long, narrow leaves and green or brown flowers whose parts are arranged in sixes. The flowers are either in a head at the top of the stem or in a cluster some way down. There are around thirty species in the British Isles, among which the most easily recognised growing along our canals is the bulrush. Most rushes grow in bogs, marshes and wet places and some can be found in the margins of canals and along back ditches and side-ponds. Like grasses, rushes are pollinated by the wind and as they do not have to attract insects, the flowers are small and unattractive. Toad-Rush is a short 15 to 20cm annual with flowers at the top of its stem and can be found growing in wet open ground, ditches, pond and canal margins. Soft Rush is the most widespread and common rush that bears its flowers some way down the stem. It has glossy green smooth stems up to 75 cm tall and forms great tussocks in wet meadows and at the edge of boggy towpaths. Hard Rush also bears its flowers below the top but is not as common. It has stiff ridged greyish green stems up to 60 cm tall. One to look out for.