There are occasions when the introduction either naturally or by man of another species to an area can cause the demise of another resident species. There are two such instances that are having a devistating effect on the fish stocks in the Fens. In general we give little thought to fish stocks in the fens out of sight out of mind so to speak. As humans we tend to favour the cute and furry or feathered variety of a species and ignore the scaley ones. Fish are a very important part of the eco-system and fish stocks in the Fens deserve to be protected as much as the other wildlife residents. Firstly the Cormorant ( carbo sinensis) which in recent years has become wide spread in the uk are have a damaging effect on fish stocks in the Fens. The Cormorant is an indiginous bird in the Uk an protected under the wildlife and country side act. therefor if a fishery owner wishes to control the numbers of cormorants on his fishery he must apply to defra for a license to cull a limited number. I myself have whitness a large colony of cormorants pearched on telegraph poles in Frithville Boston after feeding on the Maud Foster Drain.Many residents have commented on the lack of fish in the Maud Foster since the birds have arrived.There is no doubt that the same situation is occuring on other rivers and drains in the Fens. The other species being introduced to the Fens is the Otter. Once again the Otter is protected under the wildlife and countryside act. and was once wide spread throught the uk. Slowly the Otter is being introduced back into the Fens, local farmers and other groups are building man made otter holts to encourage the otter back on the fenland rivers. Ok this all sounds very worthwhile for the Otter but what will the effect be on fish stocks, only time will tell. Below are some facts about the Cormorant and the Otter.
The Cormorant can eat more than 1lb of fish per day
All Cormorants are fish eaters,dining on eels, fish and even water snakes.They dive from the surface though many species make a half jump as they dive to give themselves a more streamline entry into the water.Under water they propel themselves with their feet. Some species have been known to dive to as much as 45 metres.To survive each Cormorant needs to consume atleast 1lb of fish a day although some will eat considerably more. So a colony of 30 for example will eat atleast 30lb of fish per day which equates to over 200lb of fish per week.and multiplied by 52 the figure is astronomical. After fishing cormorants will go ashore and can be seen drying their wings in the sun.Cormorants are colonial nesters using trees rocky inlets or cliffs.There is useally one brood a year, the young feedng on regurgitated food. Latest figures show that there are now 8,355 breeding pairs and a winter population in excess of 35000 individuals.
Many Otters live in cold water and have a very high metabolic rate to help keep them warm. European Otters must eat 15% of their body weight per day ( some species can grow up to 6ft and weigh 100lbs, as you can imagine an animal this size would have to eat a lot of fish to stay alive ) depending on the temperature. In water as warm as 10c an Otter needs to catch 100grams of fish per hour to survive.Most species hunt for 3 - 5 hours a day and nursing mothers will hunt for up 8 hours per day. For most Otters fish is their staple diet,This is often supplemented by frogs, crayfish and crabs.Some will feed on small mamals and birds. Otters are very active chasing prey in the water or searching beds of rivers lakes or the sea. Different species vary in their social structure with some being largely solitary and others living in groups.