David Cabot - Collins New Naturalist Library

Freshwater fish

The first fish to come back to Ireland after the last Ice Age were the euryhaline species (those that can tolerate a wide range of salinity and are encountered in both salt and fresh water). These fish are able to maintain the concentration of chemical salts in their blood and body fluids regardless of the changes in the water around them. Thousands of years ago they almost certainly cruised around the coastline, following the northwards retreat of the glaciers, exploring the unfolding and warming aquatic systems, and penetrating the ice-free rivers and lakes. Maitland considered that the following 12 euryhaline fish colonised the freshwater systems of Ireland in early postglacial times: 50sea lamprey, river lamprey, Allis shad, Twaite shad, Atlantic salmon, brown trout, Arctic charr, pollan, smelt, European eel, three-spined stickleback and ten-spined stickleback. The latter, however, is considered by some to have been introduced (see below).

As to the stenohaline species (those that can tolerate only a narrow range of salinity), a question mark prevails over their provenance. The issue is twofold. Firstly, they are non-migratory although some, like the pike, have a capacity to spread rapidly across the land through interconnecting lakes and rivers. Secondly, they were not suited to the salt waters that surrounded all Irish shores from postglacial or earlier times. The four possible explanations for their presence are that they were already present during the last interglacial period and survived the final phase of the Ice Age in sheltered ice-free ponds; that they swam into Ireland, using the waterways in the land bridges between Ireland, Britain and the Continent; that they were once able to tolerate salt water and swam into Ireland across the sea, or that they were introduced by man or by some other agent.

The following species are generally considered to have been introduced to Ireland by man: 51brook lamprey, pike, carp, gudgeon, tench, bream, minnow, rudd, roach, dace, stone loach, perch and ten-spined stickleback. When were these first brought into Ireland? The weight of expert opinion is that probably most, if not all, were introduced sometime between the Norman invasions and the late nineteenth century. An examination of the Irish names for fish provides some corroborative insights: salmon or brown trout, not in the above list, have at least 30 different Irish names – including many local variants – authenticating their ancient presence in Ireland. By contrast, the dace and tench, both relatively recent arrivals, have only one and two Irish names respectively. 52However, this is subject to caution, as the Arctic charr and pollan, both prehistoric but rather scarce species, and not known to many, only carry a few names.

Cambrensis provides clues as to the origin of certain fish. The following translation, quoted by Went, is by Forester from Wright’s The Historical Works of Giraldus Cambrensis . 53,54

‘Sea-fishes are found in considerable abundance on all the coasts. The rivers and lakes, also, are plentifully stored with the sorts of fish peculiar to those waters, and especially three species: salmon and trout, muddy eels and oily shad. The Shannon abounds in lampreys , a dangerous delicacy indulged in by the wealthy.

This country, however, does not produce some fine fishes found in other countries, and some excellent fresh-water fishes, such as the pike , the perch, the roach, the barbel, the gardon [chub], and the gudgeon. Minnows, also, bullheads, and verones [minnows] are not found there, also no loches, or they are very rare.

On the other hand, the lakes of this country contain three species of fish which are found nowhere else. One is a sort of trout, called the salares, which are longer and rounder than trout, and which are white, close grained and good flavoured. The tymal , commonly called the umber , resembles the former kind of fishes, except that it is distinguished by a larger head. There are others which very much resemble the sea herring, both in shape and quality and in colour and taste. A third sort, exactly resembles the trout, except that it has no spots. The first sort is called Glassans, the second Cates, and third Brits. These three fish make their appearance in the summer only, and are never seen in the winter’.

It would appear from this text that the freshwater fish present in Ireland during the twelfth century included salmon, brown trout, eel, shad (probably both Twaite and Allis), sea and river lampreys, and almost certainly the brook lamprey, as the habitats of the three overlap. Amongst these early settlers, the sea and river lampreys, Atlantic salmon and the brown trout are anadromous, i.e. spend most of their lives in the sea but migrate to fresh water to spawn.

Other anadromous species arrived in Ireland from more southerly seas at the end of the last glaciation. They were the Allis and Twaite shads. Resembling herrings and found in shallow coastal waters and estuaries in western Europe, they run up the lower reaches of the larger rivers during the spawning season. In Ireland, however, the Allis shad has no known spawning site left. In fact, it is not certain whether the species is still here, as its presence is only supported by a few post-1960 records – in the Foyle estuary, Co. Derry, at two north Mayo sites, in the River Corrib, Co. Galway, and at one site in Cork. The Twaite shad shares the same coastal distribution and probably still breeds in a few Irish rivers such as the Nore, Suir and Barrow, all flowing into Waterford Harbour and the Cork Blackwater. When locked away in remote lakes, it developed into different subspecies, the Killarney shad, Alosa fallax killarnensis, being one of the most celebrated. Known locally as the ‘goureen’, it is restricted to Lough Leane and Muckross Lake, Co. Kerry, where it has been preserved for several thousand years. The smelt, also a coastal dweller in western Europe, imitates the anadromous behaviour of the shads. In Ireland it spawns in the rivers Shannon, Fergus and Foyle and perhaps at various sites in rivers Suir, Nore and Barrow. The remaining native euryhaline fish to arrive after the last Ice Age was the European eel, a catadromous species (one that migrates from rivers to the sea to spawn). Eels live in lakes and rivers and spawn in the Sargasso sea, after which the baby eels return to Ireland.

Once in Ireland the brown trout evolved a series of varieties, some of which are collectively known as sea trout (sometimes ascribed subspecific status as Salmo trutta trutta but not fully accepted by all scientists) with anadromous habits, and the darker, landlocked non-anadromous brown trout (sometimes ascribed the subspecific status Salmo trutta fario, again not fully accepted by all scientists). The latter have given rise to many other different varieties. For instance in Lough Melvin, Co. Leitrim, there are three clearly distinct stocks of brown trout: the ferox ( Salmo trutta ferox ), the gillaroo ( Salmo trutta stomachius) and the sonaghan ( Salmo trutta nigripannis) . They are genetically different and spawning takes place in different parts of the lake.

Arthur Went who, apart from being the scientific advisor on fisheries to the Irish Government, was a specialist in questions concerning the history of fish in Ireland, believed that the pike was an introduced species, basing his arguments on an examination of historical documents including the statement by Cambrensis (see here). Cambrensis had a reasonable knowledge of Irish lakes and rivers. He mentions the pike as absent from Ireland. A further clue as to the late introduction of the species is supplied by the great historian Roderic O’Flaherty, who clearly ascertained that in 1684 the pike was absent from Connacht when he wrote: