The Importance of Identifying Conservation Units: Brown Trout and Pollan Biodiversity in Ireland

Abstract

The systematics and nomenclature of European freshwater fishes, especially salmonids, are in a chaotic state. The implications of this chaos for the conservation of Irish biodiversity are outlined with reference to pollan and brown trout. The recognition of Irish pollan as a postglacial relict of the Alaskan-Siberian species Coregonus autumnalis makes it one of the most unique components of the entire Irish fauna, not just the fish fauna. Brown trout (Salmo spp) shows considerable genetic diversity that is not adequately represented by designation as a single species, and it is more appropriate to regard it as either a species complex or as separate designated species in particular areas. One example of brown trout diversity is the occurrence in Lough Melvin of three types of brown trout, known locally as gillaroo, sonaghen and ferox. These three types are genetically distinct, due to independent ancestry and natal homing to separate spawning areas, which means that minimal hybridisation has occurred since sympatry was established. They differ also in their morphology and ecology. These three types therefore merit designation as separate species: gillaroo as Salmo stomachicus; sonaghen as Salmo nigripinnis and ferox as Salmo ferox. Their conservation importance needs to be recognised, and practical conservation measures need to be put in place as a matter of urgency. Long-lived piscivorous ferox trout, which probably share a common ancestry with Melvin ferox, are found in many of the larger Irish lakes. Further work will undoubtedly reveal other unique populations. Many threats to brown trout diversity exist, including the introduction of non-native fish and invertebrate species, such as the zebra mussel, and stocking with hatchery-reared brown trout. Although the Melvin brown trout types can be designated as distinct species, conservation activities should ideally be based on local populations and communities rather than formally described taxa. This approach is limited by current European legislation but may be achievable through other facets of national fisheries and wildlife legislation.