A sampling strategy for stream populations of white-clawed crayfish, Austropotamobius pallipes (Lereboullet), (Crustacea, Astacidae)

Abstract

This paper presents an analysis of two sampling methods used to examine population size and age structure of freshwater crayfish in the River Nore catchment, Ireland. Results indicate high densities of crayfish in this river system (20-45 per in2). The combination of the two sampling methods employed (traps and enclosures) provided data on all size classes, reduced sampling selectivity and allowed estimates to be made on population densities, including juveniles. Colin F. Byrne (corresponding author), Three Rivers Project, Suir Catchment, Clonmel, Co. Tipperary; Jane M. Lynch and John J. Bracken, Department of Zoology, University College Dublin, Belfield, Dublin 4. Received 19 October 1998. Read 24 May 1999. Published 29 October 1999. INTRODUCTION The white-clawed crayfish, Austropotamobius pallipes (Lereboullet), is the only freshwater crayfish recorded in Ireland (Moriarty 1973; Matthews and Reynolds 1995). It is believed to be a native species although this is under investigation (Reynolds 1998). Austropotamobius pallipes is pro tected in Ireland under the schedules of 1 Wildlife Act 1976. It is also listed in the Appen dices EU Habitats Directive 1992. Populations of A. pallipes in the rest of Europe have declined due to competition from introduced crayfish species, pollution, habitat destruction and disease. Ireland may be seen as a unique stronghold for this species in a European context (Reynolds 1988, 1998) as there are no alien crayfish species and the occur rence of pollution, disease and other environmen tal perturbations are generally less prevalent than in the rest of Europe (Lucey and McGarrigle 1987). A number of shortcomings were identified in contemporary crayfish population studies. Most studies referred to crayfish populations in lentic as opposed to lotic riverine habitats. No single sam pling method provided an estimate of the total crayfish population. Juveniles (carapace length < 13mm) were generally underestimated or ig nored. Many methods showed similar selectivity. Crayfish behaviour has also proved to be a major problem when determining population estimates. The main objective of this study was to estab lish baseline data on all size classes of crayfish in two tributaries of the River Nore prior to the development of a lead-zinc mine in the area. To do this a sampling strategy was devised using two sampling methods, namely traps and enclosures. STUDY AREA Crayfish were sampled from five sites on two tributaries of the River Nore, which is located in the south-midland region of Ireland (Fig. 1). These were the River Goul (Sites 1, 2 and 3) and the River Erkina (Sites 4 and 5). These rivers have been under investigation since 1989 as part of an environmental monitoring programme related to a lead and zinc mine in the catchment (Byrne 1994). Physical characteristics of these sites are outlined in Table 1. All sites were riffle/glide-type habitats. Chemical analyses indicated the water was hard (276-382mg 1` CaCO3) due to the predomi nantly limestone geology of the area. The rivers sampled were nutrient rich (unfiltered molybdate reactive phosphorus 12-74gg I -' P) with prolific weed growth and well oxygenated water. The catchment is of international importance since an ecophenotypic form of the freshwater pearl mussel, Margaritffera margaritjfera (L.), known as M. m dur rovensis Phillips only occurs in the River Nore and shares the same conservation status as A. pallipes under the Habitats Directive. These are the only legally protected aquatic invertebrates in Ireland (Lucey 1998). The hardwater pearl mussel has been recorded approximately 3 km downstream of the study area in a 10-km stretch of the River Nore main channel (Moorkens et al 1992). MATERIALS AND METHODS Two methods, traps and enclosure, were used to sample crayfish populations in the catchment between August and September 1995. BioLOGY AND ENVIRONMENT: PR.OCEEDINGS OF THE ROYAL IRISH ACADEMY, VOL. 99B, Nc. 2, 89-94 (1999). 0 ROYAL IRISH ACADEMY 89 This content downloaded from 157.55.39.136 on Tue, 05 Jul 2016 06:12:35 UTC All use subject to http://about.jstor.org/terms BIOLOGY AND ENVIRONMENT R ver Erkina Du wTown