Another Life: Our pike are noble predators, not alien villains

They were blamed for declines in trout stocks when pollution, overfishing and drainage were also taking their toll

The pike, Esox lucius, is the one freshwater fish that looks at you with both eyes at once, above jutting, duck-billed jaws and spiny teeth. Even dead it can have the menace of an alligator. Coming home once in Westport, Ethna found a large pike astride the kitchen table and still remembers the shock. Her angling father, Seamus, had caught the monster in Lough Mask, where he normally fished (with trophy-winning success) for brown trout.

That was before this keystone predator – noble and necessary and of lithe and muscular beauty – began to be persecuted as an alien villain. It was blamed for declines in our trout stocks at a time when many other causes – sewage and farming pollution, overfishing, arterial drainage, competition from introduced roach – were also taking their toll. Beginning in the early 1950s, some 36,000 pike a year were culled or transferred, notably from the great trout lakes of the west.

This costly operation, widely criticised as a misguided ecological experiment, has since been somewhat reduced. Pike angling is now worth some €180 million a year. And new research, initiated jointly by Inland Fisheries Ireland and University College Dublin, has gathered a netful of new knowledge about Ireland's pike, notably that it's a native fish and eats a wide range of food beside trout. The menu is led by roach, the trout's chief competitor, but also includes frogs, birds, mice, water insects and each other's young.

A general belief that the pike was originally introduced to this island around the 1600s rested on a paper in 1957 by the fishery scientist Arthur Went. Among his evidence was that the modern Irish name for the pike, gaill iasc, identified it bluntly as a "foreign fish". It is since established that the Irish name liús was in use before the 1600s and, like the old "luce" of England, chimes with the pike's Latin surname, lucius.

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More important scientifically is the recent genetic analysis by a team led by Dr Debbi Pedreschi of UCD. Ireland's pike, it shows, arrived in two waves, first under their own steam and later by introduction. The first wave, about 8,000 years ago, used freshwater flows from melting ice sheets to swim from Europe to enter Irish rivers. Another group, in the Middle Ages, were brought by people from British waters, with descendants found mainly in the southern river catchments of the Lee and the Barrow.

Translocations of pike and changes in the canal system have led to the mixing of genes, notably in populations in waters connected to the Shannon. But the many distinct populations discovered by the new research have ecological importance. Their diversity matters even more as real and invasive aliens, such as curly waterweed and freshwater clams, increase the pressures on our ecosystems.

In the research reports (all downloadable at the Inland Fisheries Ireland website), one on the pike's dietary habits has special surprises. While the pike is distinctively shaped for fast take-off in ambushing fish, its choice of food is highly opportunist. Roach and perch dominate its fish prey, but invertebrates such as Asellus (an aquatic slater) account for more than half the diet in nearly all Irish waters.

Overall, the number of trout in Irish pike diet is currently no higher than the level of pike cannibalism. And although pike can indeed grow to giants (a 46lb fish was caught in the Erne at Enniskillen in 2009), comparatively few in Ireland reach the size for concentrating on trout as their prey.

The great adaptability of pike is reflected even in their shape: those in lakes tend to have short, deep heads, smaller eyes and deeper bodies, with more streamlined fish, with more tapered heads and larger eyes, in rivers and canals. Such “ecological polymorphisms”, say Pedreschi and her colleagues, could become important in the uncertain future of climate change. It could also mean that lake and river pike do poorly when moved between each other’s habitats.

As for the appetite for trout, the team concedes that the rapid spread of roach may well have diverted pike to an easier prey. That could change again if roach populations were to collapse through the impact of alien clams and mussels on our lake and river ecosystems.

Meanwhile, Inland Fisheries Ireland continues to remove pike from the six big western trout lakes, plus Lough Sheelin. A policy review in 2014 will let angling clubs kill rather bigger pike but make them throw back those over 90cm to live a final year and astonish pike-fishing tourists in the trout closed season.

I suspect my father-in-law had no intention of catching a pike but, finding that one had gulped a small trout on his hook, decided to play it to the boat if he could, even on such light tackle. His skill as a fly-fisher won him the Tostal angling shield in 1953 that now hangs over our woodstove.