The Arctic Char <i>Salvelinus alpinus</i> (L.) Species Complex in Ireland: A Secretive and Threatened Ice Age Relict

Abstract

Members of the Arctic char Salvelinus alpinus (L.) species complex were most likely the first freshwater fish to colonise Ireland after the last Ice Age. Once widespread and anadromous, they now form isolated populations, confined to inland freshwater lakes with suitable habitat (well oxygenated clean water, gravel shores and adequate depth when in the presence of other fish species). Adapted to Arctic conditions, they are extremely sensitive to environmental changes within their range further south, in which Ireland lies. The greatest threats to their present survival in Ireland are interspecific interactions from introduced fish species, eutrophication, acidification and climate change. The rate of extinction of entire populations has increased over the last few decades, and immediate steps must be put in place to preserve our remaining discrete populations. As marginal populations at the southern edge of the species range in Atlantic Europe, Arctic char in Ireland potentially hold some of the oldest genetic material in western Europe for the species complex. Such populations may be an important source of genetic material for the long-term survival of the species. Isolated in their respective lakes/lake catchments since the last Ice Age, they are of both genetic and evolutionary interest to scientists. This paper draws attention to the limited ecological data available on Arctic char in Ireland and attempts to place Irish Arctic char populations in context with the rest of the species' range. Where possible, recent information is given on the various aspects of the biology, distnrbution and current status of the species. Fran Igoe, Irish Char Conservation Group (ICCG), 11 Poddle Green, Kimmage, Dublin 12, Ireland (corresponding author e-mail:info@ charr.org) Johan Hammar, Institute of Freshwater Research, SE-178 93 Drottningholm, Sweden. INTRODUCTION Arctic char have a circumpolar distribution and are the most northerly-distributed freshwater fish in the world. Treated as a species complex, they belong to the genus Salvelinus, which evolved some five to ten million years ago (Power 2002). Other well known taxa belonging to this genus are the Dolly Varden (S. malma), brook trout (S. fontinalis), lake trout (S. namaycush), bull trout (S. confluentus) and the white-spotted char (S. leucomaenis). Adapted to the climatic extremes of the Arctic, the Arctic char are the only fish 'taxon' found naturally at high latitudes in the Arctic. However, they persist further south in deep, cold lakes or at high altitudes in environments that retain quasi-Arctic conditions. Relicts of a time when the polar ice sheets extended much further south, these char are referred to as marginal populations. Ireland is situated along the southern marginal zone. In this respect, outside of the Alpine populations, Irish lakes potentially hold some of the oldest genetic material in western Europe for the species complex. In the Arctic, char have evolved a range of strategies to survive and multiply. As landlocked char are often the only fish species in an impoverished environment, it is not uncommon for them to turn to cannibalism (Hammar 1998a; 2000). Further south (but still in the Arctic) many populations migrate to sea and achieve sizes up to 15kg (ohnson 1980). The bimodal size and age distribution associated with many Arctic popu lations is a reflection of thermodynamic processes (Johnson 1981; 1983; 1994; 2002) and their life history strategy patterns (Hammar 1989; 1998a; 2000). Similar situations must have prevailed in Ireland during and shortly after the last Ice Age. However, as the sea wanned and the annual cost of going to sea in terms of predation and competition for coastal food increased, Irish Arctic char lost their anadromous behaviour and became lake residents. They now live, feed and reproduce within the confines of lakes. Irish Arctic char are not physically landlocked, however, as many Irish char lakes support diadromous populations of other salmonids and eel (Fig. 1). In addition char have been recorded moving between lakes BIOLOGY ANI) ENVIRONMENT Po(XC-EEI)IN(GS O F THE ROYAL ItISH ACADFMY, V)i-. 104B, No. 3, 73-92 (2004). ( ROYAL IRISH ACADEMY 73 This content downloaded from 157.55.39.59 on Sun, 16 Oct 2016 04:44:14 UTC All use subject to http://about.jstor.org/terms BIOLOGY ANM) ENVIRLONMENT