Collins New Naturalist Library. David Cabot

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      Rainbow trout. There are only two self-sustaining populations in Ireland (J. Barlee).

      2. CARP

      Originally a central Asian species, carp was brought to England in the first quarter of the sixteenth century and to Ireland some time around 1634 on account of its potential as a food fish. Originally introduced to Ireland by Richard Boyle, Earl of Cork, as announced by his son Robert to the Royal Society in April 1663.⁶⁷ Diary entries in the autumns of 1640 and 1643 record orders given by the Earl to send both carp and tench to his friends.⁶⁸ Smith claims that both carp and tench were in the River Awbeg, Co. Cork, during the reign of James I (1603–25).⁶⁹ Like tench, carp can live in stagnant waters with very low oxygen levels (down to 0.7 mg/1) but require a water temperature of at least 18°C before they can spawn either in spring or late summer.

      3. TENCH

      Since its introduction in the seventeenth century noted above there have been selective introductions to Ireland during the past 40 years.

      4. ROACH

      Accidentally introduced to the River Blackwater, Co. Cork, in 1889, then introduced to a small ornamental lake on the River Foyle system in the mid 1920s, from where it soon escaped to colonise the river system. In the early 1970s it was illegally introduced to the Erne waterways and within ten years had colonised this large river system up to its headwaters. Since then it has been introduced to the rivers Boyne, Shannon, Corrib, Liffey, Barrow and Nore.^70,71

      5. DACE

      Accidentally introduced to the River Blackwater at the same time as the roach. Apparently two tins of each species were brought over from England as pike bait and were washed away in a flood.⁶⁵ In the late 1980s and early 1990s they were illegally introduced to Doon Lake, Co. Clare and to the lower end of the River Nore.⁷²

      Many of these introductions have upset the ecology of rivers and lakes, and led to the displacement of native species such as trout. The roach, one of the most recent interlopers and a prolific breeder, has rapidly spread from its initial area of introduction in Co. Cork some hundred years ago to colonise many river systems. It has displaced the rudd and hybridised with it, and also with bream. Apart from interspecific competition for food resources, introduced fish can bring with them fungal, viral, bacterial and other diseases. Cross-breeding with closely related species will cause genetic disruption to the disadvantage of resident species. However, fish, like other animals, are able to share out food and habitat resources. As a general ecological principle, coarse fish tend to occupy warmer, calmer and muddier waters, leaving the more turbulent, oxygen-rich and cooler areas to the native salmon and sea trout.

      The heathers

      The Ericales or heathers are to many people the most typical and interesting group of peatland plants in Ireland. They are pretty and colourful, and five species are of particular biogeographical and botanical interest. Not only do they have a restricted distribution in Ireland but they exhibit a discontinuous or relict distribution in Europe, suggesting a more widespread earlier dispersion. Such issues raise many difficult questions such as when and how did they travel to Ireland, or have they been resident here since Gortian times? Why are four of the species concentrated in a relatively restricted bogland area of west Galway and Mayo? Together with five other plant species – large-flowered butterwort, St Patrick’s cabbage, kidney saxifrage, the strawberry-tree and the Irish orchid – they form the central core of the so-called Mediterranean-Atlantic element of the Irish flora. These are the species found generally in the west and southwest of Ireland, western France, Spain, Portugal and in some western Mediterranean locations. The presence of the five heaths in Ireland, and how they accomplished and survived the transition from quite different ecological circumstances are puzzling questions. If they entered Ireland on a land bridge from north Spain during an interglacial period, why did none of them lodge in Cork and Kerry? Why did they all congregate in western Galway and Mayo?

      As the five species of heath are such special members of the Irish flora, additional information is presented on their discoveries and general ecology.

      1. DORSET HEATH

      Originally discovered in 1846 by Thomas Bergin at one very small site, close to a bog road, some 6 km southeast of Clifden, Co. Galway. Bergin presented an annotated herbarium specimen to Trinity College Dublin.⁷³ It was reported again from the same location in 1852 and then remained elusive until it was rediscovered by Lambert in 1965. Its site is a damp hollow, close to the road, and it has been suggested that the location indicates introduction by the agency of man.⁷⁴ Its growth is low and straggly, and seems at a disadvantage in relation to the nearby and taller vegetation of purple moor-grass and soft rush. The site extends no more than a few square metres with approximately five plants.⁷⁴ Its bell-like deep pink flowers are large, up to 8–10 mm, with leaves in whorls of three. The population here is unique in that there are no glands on the tips of the stout marginal hairs of the leaf.⁷⁵ It is sterile, never setting any seed of its own, but a hybrid with cross-leaved heath has been found here by Scannell. Outside Connemara it only occurs in Cornwall, Devon and further east in Dorset. In Britain it hybridises with cross-leaved heath. On the Continent it occurs in central France, Spain, Portugal and in heathy woodland in northwest Morocco. Dorset heath was present and growing in Ireland during the warm interglacial Gortian period some 428,000–302,000 years ago (see below).¹

      2. MACKAY’S HEATH

      Confined to Counties Donegal and Galway until it was recently discovered in northwestern Mayo in 1990 by van Doorslaer in a small area of raised bog near Bellacorick. The natural hybrid Erica mackaiana x tetralix (a cross between Mackay’s and cross-leaved heath) was growing nearby. In Donegal, Mackay’s heath grows on blanket bog on the shore of Lough Nacung Upper near Dunlewy, while in west Galway there are two stations – one small colony 1.5 km southeast of Carna and the other, more extensive (about 3 km²), around Lough Nalawney on the lowland blanket bog stretching southeast from Clifden to Errisbeg. The species was first discovered, prior to 1835, by schoolmaster William McAlla, who was born at Roundstone. It has shorter, broader, darker green leaves than Dorset heath, but like the latter it is sterile, for reasons not yet understood. It spreads vegetatively and the population would therefore seem to consist of a single clone from the original plant or plants. It hybridises with cross-leaved heath. The hybrid is now known as E. x stuartii. Outside Ireland it is found only in the province of Oviedo in northwest Spain, in the mountains of Castile and Asturia. Remains of leaves of E. mackaiana have been recorded in postglacial deposits from a blanket bog near Roundstone, Co. Galway⁷⁶ and from the much earlier interglacial Gortian deposit. Remains of Mackay’s, Dorset and Cornish heath have all been found in the Gort deposits as they have been in other interglacial deposits raising the possibility that they may have survived the final stages of the Ice Age and that they may not be of recent origin.^2,77