Collins New Naturalist Library

‘The water streames, besides lampreys, roches, and the like of no value, breed salmons (where there is recourse to the sea), eels and divers sorts of trouts. There was never a pike or bream as yet engendered in all this countrey, nor in the adjacent parts of Mayo or Galway counteys.’55

The pike must have been brought into Ireland some time before 1682, for historical records state the presence of weirs for eels and pike on the River Camoge at the Abbey of Monasternenagh, near Croom, Co. Limerick, at the time of the Abbey’s dissolution.56 The Civil Survey of Ireland (1654–6) also noted the River Camoge as well as other tributaries of the River Maigue had pike.57 Its widespread distribution today should not be mistaken for a sign of long-lasting presence in the country. As a rapid coloniser, the species was able, once introduced, to spread throughout freshwater systems over a short period of time.53

Went stated that there was no evidence as to whether the perch was a native species or not. However, since the remark by Young in Tour in Ireland that perch first ‘swarmed in the Shannon’ in about the year 1770, the geographic distribution of the species and its numbers have increased considerably.58 The roach, often confused with the rudd, was introduced to the River Blackwater, Co. Cork, in 1889. The barbel and ‘gardon’ – almost certainly the chub – referred to by Cambrensis are not present in Ireland today. The gudgeon, however, which the Welshman reported absent in the twelfth century, is now claimed to be a native species as are minnows – also called ‘verones’ by Cambrensis – and the stone loach.

The ‘salares’ of Cambrensis is almost certainly one of the pollan or whitefìsh species, restricted to five of the largest Irish lakes – Lough Neagh, Upper Lough Erne (no records this century), Lower Lough Erne (small but precarious population59), Lough Derg and Lough Ree (no recent records). Absent from Britain and elsewhere in western Europe, its presence in Ireland is outlandish, and it is possibly a relict from a once wider distribution. Today it is only found in the coastal areas and lower reaches of arctic rivers in eastern Europe, Asia and western North America. Once thought to be an intermediate between the powan and the vendace – both absent from Ireland – it has the status of an endemic Irish subspecies of the Arctic cisco which lives in Alaska, Coregonus autumnalis pollan. These two ‘conspecifics’, the Arctic cisco and Irish pollan, have probably been separated for about 10,000 years since the first pollan – a cold water species able to withstand life at the edge of ice sheets – are thought to have entered Ireland through the Shannon system at the start of the postglacial period.60 Although the pollan are anadromous throughout most of their northern range, in Ireland they are virtually non-migratory, and restricted to fresh waters. The species named the ‘tymal’ by Cambrensis is the grayling which, in fact, is absent from Ireland. Was it ever present or did the observer misidentify the species? It is impossible to say.

The ‘spotless’ fish referred to by Cambrensis is the Arctic charr, whose name is derived from the Gaelic ‘tarr’, meaning belly. The male belly colour ranges from pink to bright vermilion, as pointed out in two Irish names, tarr-dhearg, meaning ‘red-bellied’, and ruadh bhreac, meaning ‘red trout’.52 The female is drabber than her male counterpart whose bright red colour plays an important role both in courtship and defence of the breeding territory. Charr, more than most other freshwater fish, excite the imagination of naturalists who know them as ‘glacial, or Ice Age relicts’, i.e. survivors of the Ice Age. They inhabit the deep dark, oligotrophic (nutrient-poor) formerly glaciated lakes which they invariably share with brown trout – although in Ireland, they often break from their austere habitats and are found in shallow and eutrophic (nutrient-rich) waters. The Arctic charr is distributed throughout the northern hemisphere with both anadromous and non-anadromous populations. In Ireland, it is non-anadromous. Like the smelt and Twaite shad, it is classified as an ‘endangered and vulnerable’ species – the pollan, Killarney shad and Allis shad are ‘endangered’ species while the sea lamprey, river lamprey and brook lamprey are ‘threatened’ species.61

In an exercise of species-splitting much practised once, Regan examined various charr from Ireland and identified six ‘species’ living in different Irish lakes.62 They were: Cole’s charr, Salvelinus colii, (Loughs Eske and Derg, Co. Donegal, Lough Conn, Co. Mayo, Loughs Mask and Inagh, Co. Galway, Counties Clare and Kerry); Grey’s charr, S. grayi, (Lough Melvin, Co. Fermanagh); Trevelyan’s charr, S. trevelyani, (Lough Finn, Co. Donegal); Scharff’s charr, S. scharffii, (Loughs Owel and Ennell, Co. Westmeath); Coomasaharn charr, S. fimbriatus, (Coomasaharn Lake, Co. Kerry) and blunt-nosed charr, S. obtusus, (Loughs Tay and Dan, Co. Wicklow, and Loughs Leane and Acoose, Co. Kerry). Today these are regarded as different local forms of the single species Arctic charr.63 Since 1930, the Arctic charr has been recorded in 32 lakes in western Ireland ranging from Lough Fad, Co. Donegal, to Lough Inchiquin, Co. Kerry, together with Lough Dan, Co. Wicklow. Several other lakes, especially those suffering from eutrophication, have lost their populations of this pollution-sensitive salmonid.61

The freshwater fish that have been indisputably introduced to Ireland, and for which there are reasonably good historical records, include the following five species.

1. RAINBOW TROUT

Introduced to Ireland from western North America in 1888 when eggs were sent to hatcheries at Inishshannon and the River Bandon, Co. Cork, and Ballymena, Co. Antrim.64 Spawning takes place at about 40 sites in Britain and Ireland but the populations are self-sustaining at only six, including three in Ireland. One site was at Lough Shure, Aran Island, Co. Donegal, where they were recorded present in 1940, and the second was at White Lough, Co. Westmeath, where they were introduced by the Inland Fisheries Trust in 1955.64 Breeding was recorded at the third site, Lough na Leibe, Ballymote, Co. Sligo, in 1971 (originally stocked in 1955 by the Inland Fisheries Trust). In all cases their present status is unknown.65,66 Elsewhere most populations are maintained by the continued introduction of hatchery-reared fish.

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

Mackay’s heath at Lough Nacung Upper, near Dunlewy, Co. Donegal. Very similar to crossleaved heather but has a stronger and bushier habit.

St. Dabeoc’s heath with its urn-shaped corolla.

3. ST DABEOC’S HEATH

Confined to but very numerous in some locations in west Galway and in south and west Mayo from near Cong and Partry to the Killary Harbour and Croagh Patrick, and at Corraun on Achill Island. It was first unwittingly discovered by Edward Lhwyd, the great Welsh naturalist and antiquarian, who found it growing in most of the mountains of Galway and Mayo during a visit, probably mid May 1700. At the time he did not know it was St Dabeoc’s heath, describing it as ‘…an elegant sort of Heath, bearing large Thyme-leaves, a spike of fair purple Flowers, like some Campanula, and various stalk…’. He brought his specimens back to London and presented several to his friends there, including the botanist Petiver who later identified and described it in 1703.78 It is a small undershrub with straggly branches, often growing up through heather or gorse. Its leaves are narrow, elliptical, shiny green on top and whitish underneath. The large purplish corolla is about three times the size of those of bell heather. It is absent in Britain but found in southwest France as far north as the River Loire, and especially in the Cantabrian mountains, in the Spanish peninsula and the Azores. In the Pyrenees it survives quite happily under a snow covering for five months each year, belying the notion that it is a tender Mediterranean plant.

4. IRISH HEATH

First found by Mackay in 1830 on Errisbeg, near Roundstone, Co. Galway, and later in other localities in west Co. Galway. In Co. Mayo it is present at the mouth of Killary Harbour, on Clare Island, at Bellacragher Bay (north of Mallaranny), northwards to the Mullet peninsula and eastwards to Lough Conn (west and eastern shores). It is absent from Britain. The single station northwest of Bordeaux in southwest France is probably extinct.75 It occurs in good quantity in Portugal and in northwest Spain. Unlike the other heaths in Ireland, it may start flowering in January with the blooms at their finest in April, producing one of most magnificent botanical sights in the country. This hairless shrub forms dense stands, sometimes as high as 3 m, both at sea level (Praeger once observed it adorned with seaweed thrown up during storms) and on the mountainside (up to at least 155 m) rising up from the head of Bellacragher Bay. The sight of it here in early spring is a truly remarkable botanical feast.79 On the Bellacragher Bay mountainside the heather tracks the snaking pathways of small streams and rivulets that provide the plant with extra nutrients and moisture. Irish heath is also found further south, in the remarkable area of lowland blanket bog between Roundstone and Clifden, Co. Galway, that was covered with woods in the aftermath of the last glaciation. Jessen showed from the analysis of pollen remains found in the muds that Irish heath was growing in those woods, as it does in northwest Spain today.77 How it successfully survived the transition from a protective woodland environment to the barren, bleak and windswept blanket bog habitats in the west of Ireland is a tribute to its adaptive capabilities. Unlike the two other rare heaths, Dorset heath and Mackay’s heath, it is fertile and reproduces by seed. It has been argued by Foss & Doyle that it could have been introduced to Ireland by man some 500 years ago, at a time when there were direct trade links between Ireland, Spain and Portugal. Irish heath is found growing close to many pilgrimage shrines and abbeys in Portugal, Spain and France and it is postulated that it could have been carried by pilgrims.80

5. CORNISH HEATH

Originally found by Major Dickie of Enniskillen, but first reported by Praeger in 1938.81 It was growing on an isolated blanket bog near Belcoo, Co. Fermanagh, with white flowers (normally lilac-pink), and Praeger sided with those who considered the plant indigenous in a native habitat. Webb visited the bog in 1954 and reckoned that ‘the force of arguments were in favour of regarding it as native’.82 The site, close to a mineral flush, was visited in 1965 and 1966 by McClintock when about 1,000 plants were recorded.83 Another historical site was reported by Robert Burkitt in the 1850s, on the cliffs of Islandikane townland, west of Tramore, Co. Waterford, but the species has not been seen there since, despite repeated searches. It was naturalised on the sand hills at Dundrum, Co. Down, where it was discovered by Swanston in 1899, and was still present in 1978.84 It also grows on the rocky shore at Shane’s Castle, Co. Antrim. Outside Ireland it occurs in heaths in south Cornwall, and elsewhere in western Europe. It is a short to medium hairless undershrub with flowers ranging from white to pink to lilac. No evidence has yet been produced to show that Irish heath was a member of the Irish interglacial flora. Their seeds are consistently larger (c.0.7 mm) compared with c. 0.5 mm of other Erica species, so it would have been difficult to overlook them in samples of interglacial deposits.85

Irish heath with western gorse at Ballacragher Bay, Co. Mayo.

The Connemara and Burren plant assemblages

The congregation of the above ericaceous species in western Connemara is one example of apparent geographical plant madness, but the eclectic agglomeration of rare flowers in the Burren, Co. Clare, with representatives of arctic, alpine and Mediterranean floras also begs explanations. What could be the origin of such an unlikely association?

One interpretation postulates that these species originally had a more widespread range in Ireland. Although the Pleistocene glaciers probably wiped much of the landscape clean of living resources, some plants may have been able to avoid the ice blanket by moving up to the highest mountain peaks or sheltering in other refugia. Others, however, possibly shifted westwards to ice-free offshore islands and peninsulas. The sea level started to drop around 35,000 years ago, reaching its maximum fall of some 130 m below present day levels around 15,000 years ago. The west Clare and Connemara coastlines could then have extended perhaps some 45 and 10 km respectively west of today’s shorelines.2 Admiralty charts show commodious areas off the Burren coast stretching beyond the Aran Islands which would have been uncovered and well above water during the Ice Age. Assuming that the North Atlantic Current exercised some warming influence, the glaciers could not have impacted those areas. It is therefore possible that the plants may have survived in isolation on mist-shrouded, ice-free banks. As the glaciers withdrew and the sea started to rise again, the plants would have had to move back to the mainland. Despite the vegetative reproduction of most alpine species and presumed slow migration rates, the long time spans associated with the waxing and waning of the glaciers would have been sufficient to permit the relatively short migrations from the Burren and Connemara to those western tips and back again. Survival of plants during the first glacial epochs of the Ice Age on the summits of the Burren hills can probably be ruled out as all of them are too low to have escaped a scouring of the ice sheets (the highest is Slieve Elva at 344 m). However, several Burren hills were glacier-free during the last Midlandian glacial phase, towards the end of the Ice Age.

An alternative hypothesis regarding the survival of plants put forward by Mitchell & Ryan envisages a general migration of the various Burren and Connemara curiosities as well as other Lusitanian plant species up and down the western Atlantic seaboard from the Irish west coast to the shores of Spain and Portugal. In support of their western seaboard migration route hypothesis they quote the present known distribution of the shore-living bug Aepophilus bonnairei in Ireland, southern England, west Wales and the Isle of Man. Its modern day distribution centre is the Atlantic coast from Morocco to Portugal. If the bugs had been present in Ireland historically, they would not have survived the cold Nahanagan snap and must have ‘marched’ up along a western seaboard land bridge as temperatures rose some 10,000 years ago. Additional support for the southern route to Ireland for Lusitanian species comes from detailed pollen studies carried out by Fraser Mitchell,2 which show that pine, oak and alder followed the proposed route taken by Aepophilus across the ‘dry’ Bay of Biscay to the Celtic Sea and then into southern Ireland. However, the question of sea barriers and the long distances involved make this hypothesis less convincing. The introduction of seeds by migrating birds travelling northwards from Spain and Portugal is also improbable as most seeds of the Burren and Connemara curiosities are not eaten by birds.

Western Connemara, Co. Galway, the location of rare plant assemblages.

Devoy has discussed five possible land bridge connections between Ireland and Britain, including the Continental shelf, across which flora and fauna could have moved into Ireland when the country was released from the grip of ice during the late Ice Age.86 Devoy considered that the route from the south, across the Continental shelf, along which the southern Lusitanian species would have travelled, would have been problematical. An interconnected series of channels and troughs off the south coast of Ireland led west and southwest into canyons lying at a greater depth than 100 m below today’s sea level. The movement of meltwaters and sediments over this area at the time even when sea levels were much lower than today would have created adverse conditions (pools, channels, rivers, etc.) for species sensitive to water, and made it very difficult, if not impossible, for plants to move dry-shod from Portugal, northern Spain and western France into Ireland. Thus the southern entry route for the so-called Lusitanian and other Mediterranean species now present in the Burren and in Connemara seems to be ruled out. Entry into Ireland of these species across the other four land bridges traversing what is now the Irish Sea is not supported by any historic or present day evidence. Survival of these species, many of which were already present in Ireland, in ice-free areas or refugia (off the west coast) thus appears to provide the most plausible explanation to account for the curiosities of Clare and Connemara.