Otter (Lutra lutra): Expert fisherman of broadland and fen.
PREDICTABLY UNPREDICTABLE -- it's the only way I could describe the results of a 5-year study of otters' movements on a river local to my home of the time. It didn't matter how often I thought I was getting close to determining a chronological pattern of their comings and goings up and down the river -- in order to give myself a brief glimpse as they popped out of the water to anoint a favourite territorial marker -- as soon as I thought I had cracked it, they undermined my findings and sent me back to the drawing board. Persistence pays-off however, for all of my hours of staking-out these favoured markers, I was rewarded with fleeting views of the aquatic mammals, turned to a silvery sheen as they went about their nocturnal business under the reflected light of the stars and the moon.
The slow meandering rivers of the Norfolk Broads, mile after mile of ditches running through pristine grazing marshes and the large open bodies of water that form the broads themselves make for the equivalent of an otter Nirvana, offering the perfect blend of abundant fishing grounds and quiet backwaters where mothers can raise their cubs. The otters that we encounter in Norfolk and elsewhere in Britain are members of the mammal family Mustelidae -- the weasels -- further divided into the sub-family lutrinae, the river otters. This particular tribe of otters historically range from Britain, through Western Europe, across Asia and into Japan, even inhabiting the northern tip of Africa. Although Britain's otters suffered a calamitous weakening of numbers during the 1960's and 1970's, due chiefly to toxins from agriculture building-up in the river networks combined with habitat loss, they are now back where they belong, offering naturalists the best chance in a generation to observe their behaviour.
As elusive as they are, otters leave a trail of evidence behind that betrays their presence, which, once learnt, can lead to some memorable encounters. The evidence takes the form of spraints -- sweet smelling deposits that are a combination of fish bones and scales bound together with a jelly secreted from anal musk glands -- the otter's equivalent of a text message, passing on information to other otters travelling through a particular stretch of river such details as age, gender, state of health and, in the case of females, readiness to mate. The spaints are left in conspicuous locations throughout the animal's home range -- the roots of fallen riverside trees, rocks, tufts of grass, confluences of streams and most obvious of them all, under bridges where they are protected from the elements -- acting as telegrams and territorial markers used by successive generations of otters. The ability to identify these dark, scaly, jasmine scented emissions is crucial in tracking down the water-loving mammals.
Research suggests that a dominant dog otter may require up to 25-miles of linear water as a territory, where he will welcome the presence of two adult females and their young cubs. The river, with its adjoining lakes and feeder streams will need to be in pristine condition with a healthy population of suitable prey for the otters. Perch, bream, stickleback, eels and other course fish form 95% of the otters diet; brown trout is a favourite but generally too fast to catch. Requiring 1.5kg of food a day -- up to 12% of their body weight -- keeps the animals busy throughout the dawn, the dusk, nighttimes and even into the daylight hours. Twilight is the best time to catch a glimpse of them as they glide across channels that connect one body of water to another, the mirror smooth water broken only by a whiskered muzzle and dark, searching eyes. If they suddenly dive for fish, follow the trail of bubbles rising to the water's surface, for they will emerge within 10 - 20 seconds, allowing you to follow their liquid movements for a little while longer.
Young otter cubs are not natural swimmers; they have an inherent fear of the water. Only when they are three months old, once a dense, oily adult coat has developed will they get their webbed-feet wet for the first time, courtesy of their mother grabbing them by the scruff of the neck and dragging them into the drink!
Power and fluid grace combine as a dog otter swims purposefully towards a sprainting site. The defined bow wave created around its body betrays the speed at which these aquatic mammals can travel in water.
Sometimes this is the only view you get of an otter, the animal detecting your presence before submerging itself under the water's surface. On this occasion, it was fishing for breakfast on a misty March morning, shortly after sunrise.