Whitefish – few and far between

Whitefish – few and far between

Whitefish are related to the trout and salmon and possess the adipose fin typical of game fish. A small fleshy fin with no rays, it is sited between the dorsal and the tail fins. Whitefish differ from their salmonid relatives in possessing large scales (a lot fewer than either trout or salmon), and in having virtually toothless jaws and a small mouth. They are pale in colour, the back being greeny-blue and the sides and belly silvery to white. It is this absence of dark colour that gives them their name – whitefish.

What’s in a name?

Three species of whitefish live in the British Isles, all in lakes in the north-west. However, over the years there has been enormous confusion about their identity and, indeed, about how many species there were in our islands.

The problem was caused partly by their isolation — they are found in widely separated lakes, and each population had acquired a separate common name — and partly because over centuries of isolation each population had evolved to possess slightly different features. This led scientists to give a distinct scientific name to each species or sub-species they thought they had recognized.

Since whitefish are also found across the whole of Europe, northern Asia and North America, many in lakes similar to those in Britain, the number of populations bearing scientific names was immense.

However, modern studies have now produced a situation where only three species are recognized in Britain. All three are also found in Europe or North America.

The first species is Coregonus lavaretus: it lives in Loch Eck and Loch Lomond in Scotland, where it is known as the powan; in Haweswater, Ullswater and the Red Tarn in the English Lake District, where it is called the schelly; and in Llyn Tegid (Lake Bala) in Wales, where it goes by the name of the gwyniad.

Another, somewhat smaller, species — the vendace (Coregonus albula) – lives in Derwentwater and Bassenthwaite in the Lake District. It was formerly found in Castle and Mill Lochs at Lochmaben in Dumfriesshire but is now believed to be extinct there.

The third species, Coregonus autum-nalis, known as the pollan, lives in Ireland in Loughs Neagh, Dearg, Ree and Erne. In many ways this is the odd one out since its nearest relatives seem to live in western

North America; the other two species are found in many lakes in northern Europe and the Alps.

How did they get here?

The whitefish are believed to have lived in the immense ‘ice lakes’ that covered large areas of Europe at the end of the Ice Ages, but they may also have lived in the low salinity seas surrounding the partly frozen land mass, migrating into rivers every year to spawn. Over thousands of years these ‘ice lakes’ disappeared as the glaciers melted, causing the land to rise as the weight of ice was removed.

The result seems to have been that populations of several kinds of whitefish (probably very closely related) became stranded in geographically restricted areas and eventually land-locked in the lakes in which we know them today. Ten to fifteen thousand years of isolation have caused tiny changes in each population in response to slight differences in environments.

Feeding and breeding

The whitefish in Britain feed mainly on minute crustaceans, particularly daphnia (water fleas) and copepods, but as they grow larger they eat insect larvae and even bottom-living molluscs as well. In winter, when planktonic crustaceans are scarce, they tend to feed near the lake bed on a variety of insect larvae.

They spawn in early winter, laying their eggs on gravelly lake beds, usually in moderate depths. The orange eggs take up to 10 weeks to hatch. The fry then feed on their yolk sacs for a few weeks, ensuring the young fish begin to swim in early spring— a time when the smallest planktonic creatures are readily available.