D. Doherty, N. O Maoiléidigh and T.K. McCarthy ABSTRACT

Transcription

1 THE BIOLOGY, ECOLOGY AND FUTURE CONSERVATION OF TWAITE SHAD (ALOSA FALLAX LACÉPÈDE), ALLIS SHAD (ALOSA ALOSA L.) AND KILLARNEY SHAD (ALOSA FALLAX KILLARNENSIS TATE REGAN) IN IRELAND D. Doherty, N. O Maoiléidigh and T.K. McCarthy ABSTRACT Anadromous twaite shad (Alosa fallax Lacépède) and allis shad (Alosa alosa L.) occur in Irish coastal waters, although only twaite shad has been confirmed to reproduce in Ireland. A landlocked subspecies of the twaite shad, known as the Killarney shad (Alosa fallax killarnensis), occurs in Lough Leane in south-western Ireland. Relatively little scientific research has been undertaken on the marine phases of these species in Ireland except for occasional reports of coastal bycatch. The growth, diet and parasite assemblages of twaite and allis shad sampled from Waterford Estuary and the upper tidal reaches of the River Barrow have been investigated since Similarly, aspects of the Killarney shad have been investigated since The number of gill rakers or general body size easily separates these subspecies of shad. The perceived threats to the twaite, Killarney and allis shad in Ireland, where they have been categorised as vulnerable to extinction (twaite shad) and endangered (Killarney and allis shad), are listed and discussed. D. Doherty (corresponding author; denis.doherty@ mail.esb.ie), Electricity Supply Board, Ardnacrusha, Co. Clare, (via Limerick), and Zoology Department, National University of Ireland, Galway; N. O Maoiléidigh, Marine Institute, Fisheries Research Centre, Abbotstown, Dublin 15; T.K. McCarthy, Zoology Department, National University of Ireland, Galway. INTRODUCTION The genus Alosa is represented in the British Isles by twaite shad (Alosa fallax Lacépède) and allis shad (Alosa alosa L.). In addition, the Killarney twaite shad or goureen occurs in south-western Ireland. This unique landlocked dwarf twaite shad was assigned subspecific status in 1911 as Alosa fallax killarnensis by Regan (1916) from a specimen taken from Lough Leane, Killarney. Regan was of the opinion that the specimen must have been part of a colony of twaite shad that had remained in the lake and now formed part of a non-migratory lacustrine group (Regan 1916). Aprahamian et al. (2003) suggested that the Lough Leane population existed in isolation due to local tectonic changes. The only other known European lacustrine twaite shad occur in several of the northern Italian lakes, i.e. Alosa fallax gracilis Regan in Lake Garda and A.f. lacustris Fatio in Lakes Como, Lugano and Maggiore (Trewavas 1938). Trewavas stated that the goureen or lake herring, as they were known locally, spend their entire life cycle in the lakes without migrating to the sea. Despite heavy netting by draft nets in the lower estuary of the Killarney lakes system over the past 30 years, there is no evidence of a contemporary anadromous twaite shad population in the lakes. In contrast, the anadromous migratory shads of the Mediterranean still enter Italian rivers and lakes inhabited by the lacustrine form (Trewavas 1938). A map of the current distribution of shad in Ireland is shown in Fig. 1. There have been occasional records from locations around the Irish coast, and these have been referred to in general accounts of rare and endangered Irish fishes (Bracken and Kennedy 1967; Whilde 1993; Maitland 1996). However, many of these records are historical, and there is no clear knowledge of their current distribution. Fahy (1982) analysed variation in bycatch of A. fallax from net fisheries in Wexford Estuary. O Maoiléidigh et al. (1988) examined the two forms of twaite shad using electrophoretic and multivariate analyses of their morphometric and meristic character sets. Doherty and McCarthy (2001) investigated aspects of the spawning anadromous twaite shad and transitory non-spawning allis shad from Waterford Estuary and the River Barrow. The study involved aspects of the ecology, growth, parasites, diet and fecundity of both species of BIOLOGY AND ENVIRONMENT: PROCEEDINGS OF THE ROYAL IRISH ACADEMY, VOL. 104B, NO. 3, 93/102 (2004). # ROYAL IRISH ACADEMY 93

2 BIOLOGY AND ENVIRONMENT Fig. 1*/The location of twaite shad records in Ireland: 1. River Foyle; 2. Castletown River; 3. River Boyne; 4. Nanny River; 5. River Liffey; 6. River Slaney; 7. River Barrow; 8. River Nore; 9. River Suir; 10. River Blackwater (Munster); 11. River Lee; 12. River Bandon; 13. River Ilen; 14. River Laune; 15. Lough Leane; 16. Dundalk Bay; 17 East of Lambay Island; 18. Waterford Harbour; 19. River Eske, and 20. River Feale. Allis shad have been captured occasionally from the Irish and Celtic Seas (Bracken and Kennedy 1967) and also from Waterford Estuary (Doherty and McCarthy 2001). A detailed map of the St Mullins area on the River Barrow is also shown, indicating the area fished during the annual shad fishing competition and the spawning site below the weir. anadromous shad. In addition, their morphometric and meristic character sets were also analysed using multivariate analysis. According to Whilde (1993), allis shad are thought to be endangered, while twaite shad are vulnerable. Both species are much less common than formerly over their European range, including Ireland (Maitland 1996). Due to the decline in abundance of Alosa spp, the species have been included in Appendix III of the Bern Convention and in Annexes II and V of the EU Habitats Directive (Aprahamian et al. 2003). European populations of allis and twaite shad are in decline due to overfishing in estuaries, obstruction of river migration by pollution, dams and weirs, and habitat destruction resulting from pollution and engineering works. This paper aims to summarise the current knowledge and status of the Alosa genus (two species and one subspecies) and to review their conservation status and discuss possible threats to the shad species in Irish waters. DIFFERENTIATION OF THE THREE SHADS All of the shads are members of the herring family, Clupeidae. In general body form they are deepbodied and laterally compressed, with large, easily detached scales. The number of gill rakers on the first gill arch and the geographical location of the subspecies effectively separate the two Alosa species. Twaite shad have 35 /60 gill rakers (depending upon size) and allis shad have 80 /155 (dependant upon size). Killarney shad have between 43 and 53 gill rakers (Wheeler 1969; Sabatié et al. 2000; Aprahamian et al. 2003). Extensive variation and hybridisation have been recorded among European populations (Alexandrio 1996). The presence of hybrid fish in Ireland is thought to be doubtful as there is no known Irish spawning site for allis shad (Doherty 1999). Apart from the obvious differences in body size (the allis shad being larger), a combination of shape differences in the morphometric character sets allows for differentiation between the two anadromous shad species on the basis of their morphometric and meristic character sets (Doherty and McCarthy 2001). O Maoiléidigh et al. (1988), in a comparative study of the two forms of Irish twaite shad, reported that apart from the dwarfed appearance of the lacustrine Killarney shad and the increased number of gill rakers carried on the first branchial arch, a broad overlap occurred in the meristic character sets. Furthermore, no consistent shape differences were observed between the two forms of twaite shad. O Maoiléidigh et al. (1988) reported that the taxonomic position of the Killarney shad was uncertain in that it differed phenotypically from other twaite shad but displayed few genetic 94

3 BIOLOGY, ECOLOGY AND FUTURE CONSERVATIONS Fig. 2a*/Allis shad Alosa alosa. Reproduced with the kind permission of Peter Maitland. Fig. 2b*/Twaite shad Alosa fallax. Reproduced with the kind permission of Peter Maitland. differences. These authors advocated the retention of a subspecific name for Alosa fallax killarnensis because it served to focus attention on a unique Irish lacustrine population. More recently, Kottelat (1997) suggested reclassifying Alosa fallax killarnensis (Regan 1916) as a separate species and proposed Alosa killarnensis Regan, 1916 as the valid scientific name. ECOLOGY OF THE SHADS GROWTH AND LIFESPAN Twaite shad sampled from the River Barrow in 1996 and 1997 by Doherty and McCarthy (2001) ranged from 202mm to 429mm in length and 182g to 1178g in weight and were 2 to 7 years old. Allis shad sampled in 1996 and 1997 were larger and older, ranging from 386mm to 504mm long and 988g to 1775g in weight and were 5 to 9 years old. The growth curves of Irish and European populations of twaite and allis shad are shown in Fig. 3. Growth of Irish twaite shad is broadly similar to other European populations, though Quignard and Douchement (1991) reported that growth rates and longevity of both twaite and allis shad varied with locality. The age and weight of a small sample of allis shad from Waterford Estuary indicated that these were the slowest growing and smallest when compared with other European allis shad populations as described by Quignard and Douchement (1991). This may be due to the small sample size (n /12) or because these were occurring at the edge of their European range. A gill-netting survey of Lough Leane carried out in 1985 and 1986 captured Killarney shad from 3 to 5 years old. Back-calculated growth data obtained from the 1985 and 1986 surveys of Lough Leane are given in Table 1. SPAWNING AND LIFE HISTORY In Ireland, the only known spawning population of anadromous twaite shad occurs in the upper tidal limit of the River Barrow as shown in Fig. 1. According to Doherty and McCarthy (2001), it is doubtful that a spawning allis shad population occurs within the Nore, Suir or Barrow rivers discharging into Waterford Harbour because only immature allis shad were captured in their study and there is neither documented nor anecdotal evidence 95

4 BIOLOGY AND ENVIRONMENT of spawning. These allis shad probably represent transitory non-spawning migrant fish. The nearest known reproducing population is in northern and western France (Quignard and Douchement 1991). The spawning habits of both species of shad are broadly similar, although there are some differences in timing and location (Boisneau et al. 1992; Alexandrio 1996). Both species enter the upper reaches of large European rivers during the spring months after reaching sexual maturity at 3/7 years old (Boisneau et al. 1992; Assis 1990). In Ireland, where only twaite shad are known to spawn, mature fish enter the River Barrow from April to June, with peak spawning activity occurring in late May. Considerable variation in activity may occur depending upon water temperature, tidal strength and river flow. Mature males were younger and significantly smaller than females (Doherty and McCarthy 2001). Doherty (1999) found that gravid female twaite shad on the spawning site at St Mullins on the River Barrow had a mean age of 5.6 years, compared to younger males that were 2.95 years old. Sexual dimorphism also occurred in the two shad species, the females being significantly larger in size. According to Quignard and Douchement (1991) spawning usually occurred near a confluence, but may be anywhere along a river where the current is fast enough and where the bed is mainly gravel with a water depth of less than 1.5m. During the spawning period, adults moved to the spawning grounds at night and left at the break of day. According to Aprahamian et al. (2003) water temperature ( /128C) is the most important environmental factor moderating spawning migratory behaviour. The description of French spawning sites is similar to the River Barrow spawning site as shown in Fig. 1. On the River Barrow, spawning occurs immediately downstream of the last navigation weir located at the uppermost tidal limit (Doherty 1999). Spawning usually begins at dusk and occurs where the water depth generally ranges from one to two metres. Eggs are released directly into the water column, where they sink into the gravel bed of the river, hatching 4/8 days later. The fry, which are approximately 10mm in length upon hatching, grow rapidly and reach 14 /18cm after one year (Maitland and Campbell 1992). Adults return to the sea almost immediately after spawning, whereas the young fish move downstream to the estuary in the autumn (Wheeler 1969; Claridge and Gardiner 1978; Aprahamian 1988). In 1996 and 1997, River Barrow twaite shad congregating at the spawning site had gonad: somatic index (GSI) values (mean9/standard deviation) of 16.59/7.3 (18.89/7.5 for females and 11.49/2.9 for males) (Doherty 1999). This Length (mm) Length (mm) (a) (b) France (Loire) France (Adour) France (Garonne) Ireland (R. Barrow) Age (years) France (Loire) France (Adour) Age (Years) Fig. 3*/The growth in length of some European populations (Quignard and Douchement 1991) of (a) female and (b) male twaite shad along with twaite shad sampled from Waterford Estuary and the River Barrow (after O Maoiléidigh 1990; Doherty and McCarthy 2001). France (Garonne) Ireland (R. Barrow) 96

5 BIOLOGY, ECOLOGY AND FUTURE CONSERVATIONS Length (mm) Age (years) Loire, France Garonne, France Adour, France Duoro, Spain Waterford estuary, Ireland Fig. 4 */The growth in length (mm) of some European populations (Quignard and Douchement 1991) of allis shad including a sample from Waterford Estuary (Doherty and McCarthy 2001). compares to 3.19/4.2 (3.69/4.5 for females and 0.49/0.0 for males) for a post-spawned estuarine sample captured from Waterford Estuary in the same years (Doherty 1999). According to Quignard and Douchement (1991) the GSI of French and Portuguese twaite shad populations increased rapidly one or two months prior to spawning, with high values reported at spawning time due to the loss of somatic weight. However, Quignard and Douchement (1991) stated that twaite shad GSI values may differ from year to year and from site to site, e.g. males (and females) of the Loire River had GSI values of 7.8 (12.2); the Ardour River, 9.1 (16.4); and the Rhône River, 7.7 (18.7). Annual variation of a twaite shad population is evident in records of the annual twaite shad angling competition on the River Barrow, which is operated on a catch-and-release basis. The records of the competitions, together with those of the Irish Specimen Fish Committee (ISFC), may give an indication of the annual variation in numbers of spawning twaite shad in the River Barrow. The ISFC maintains records of large rod-caught fish referred to as specimen ( /0.964kg) twaite shad. There was considerable interannual variation (Fig. 5) in the number of specimen twaite shad reported by anglers from the River Barrow between 1980 and 2001 (n /305, mean9/sd/ 13.59/13.96, range 0 /41). Over 99% of these shad were caught between March and June. Catches are influenced by tidal cycles. No specimen allis shad ( /1.814kg) have been recorded in Irish waters by the ISFC within the past 46 years (ISFC 2001). The weight frequency distributions of these specimen twaite shad are shown in Fig. 6. Lough Leane shad are reported to spawn on gravel bars and gravelled shallows surrounding the larger islands in the lake between June and early July. However, the exact location of these sites is unknown (O Maoiléidigh 1990). The length of Killarney shad sampled by gill nets of variable mesh size in 1985 and 1986 was between 17.0cm and 22.4cm (Table 1). In both years the mean size of the females was considerably larger than that of the males. An examination of the scales of Killarney shad showed a predominance of four-year-old fish. Only one fish over five years was taken, and it is likely that the life span of Killarney shad is quite short. However, the population age structure was not apparent for the 1985 or 1986 sampling programmes, as the gill nets did not sample the lower age groups. In contrast to the anadromous twaite shad from the River Barrow, the Killarney shad scales did not display the same degree of spawning erosion on the scale edges. This probably reflects the shorter migration and the less exhaustive spawning activity of the Killarney shad compared to the anadromous spawning run (O Maoiléidigh 1990). The sex ratio of the Killarney shad did not differ from a 1:1 ratio (Chi 2 /3.4, P/0.063). However, the sex ratios changed considerably during the 1986 sampling period. Prior to spawning, male fish dominated the samples; subsequent to spawning, there was almost an equal ratio of spent male and female fish. DIET AND PARASITOLOGY The variation in feeding intensity of spawning French populations of twaite and allis shad recorded by Quignard and Douchement (1991) has also been noted in River Barrow twaite shad (O Maoiléidigh 1990; Doherty and McCarthy Table 1*/A comparison of back-calculated length at age of Killarney shad sampled during 1985 /6 (O Maoiléidigh 1990). L1 (cm) L2 (cm) L3 (cm) L4 (cm) L5 (cm) Range 2.5 / / / / n

6 BIOLOGY AND ENVIRONMENT 2001). Both of these studies reported that feeding ceased during the spawning period. Doherty and McCarthy (2001) reported that post-spawned estuarine twaite shad sampled from Waterford Estuary fed to a large extent on invertebrates, although piscivory appeared to be particularly important for the larger specimens of both shad species. Adult twaite shad actively fed on marine mysids Praunus neglectus (G.O. Sars), which formed 99.9% by number and 96.8% by weight of stomach contents. The remainder of the diet was made up of small sprats, Sprattus sprattus (L.). The relatively larger allis shad, although fewer in number, also fed extensively upon the marine mysid P. neglectus. Three marine fish species*/whiting (Merlangus merlangus (L.)), sprats and European smelt (Osmerus eperlanus (L.)) were recorded in allis shad stomachs, fish making up a significant proportion by weight of the diet. A small number of shrimps, Crangon allmani Kinahan, were also recorded (Doherty and McCarthy 2001). In the River Severn, twaite shad were found to feed upon a range of prey, with preferential items being fish and secondary items including mysids, shrimps, isopods, detritus and other aquatic insects (Aprahamian 1988). According to Quignard and Douchement (1991) large allis shad are plankton feeders, with the main food being copepods (Calanus sp.), decapods (Pandalus sp.), euphausids (Meganyctiphanes sp.) and young fish. Bracken and Kennedy (1967) reported that the diet of adult twaite and allis shad captured in the Irish Sea consisted of zooplankton and small euphausids. The parasite species assemblages, as recorded by Doherty and McCarthy (2001) and listed in Table 2, were found to be similar for both anadromous Alosa species. All of the parasite species were new Irish host records, although they all had been previously reported from other European twaite and allis shad populations (Aprahamian 1985; Quignard and Douchement 1991). Differences noted in parasite species infection levels of the two shad species may be due to the specificity of the parasite or aspects of the host fishes such as dietary preferences or movements at sea. Dietary analysis of Lough Leane Killarney shad (n /32), sampled in a gill-netting survey in June 1985, demonstrated that stomach contents were almost exclusively composed of zooplankton (Table 3). Daphnia longispina Müller was found in all stomachs that contained food. D. longispina represented 93% of the total numerical abundance of all food items (Table 3). The next most important food items were copepods, which were found in 82% of stomachs. Numerically they were less important than the Daphnia spp (4.8%). The pupating chironomids and ceratopogonids also found were probably migrating through the water specimens of No Year Fig. 5 */A histogram showing the number of specimen (/0.964kg) twaite shad recorded in Irish waters during the period 1980/2001. A total of 305 specimens were captured on the River Barrow at St Mullins, while one specimen was captured on the River Suir in 1992 (Irish Specimen Fish Committee 2001). fish) of (no. Frequency Weight (kg) Fig. 6 */A histogram showing the weight frequency distribution of all specimen twaite shad (n/305) recorded in Ireland from 1980/2001 (Irish Specimen Fish Committee 2001). column when eaten by the shad. Water mites and Argulus spp also formed a small portion of the diet, but whether they were deliberately selected or ingested accidentally while feeding on plankton is not clear. The Italian lacustrine form of twaite shad (Alosa fallax lacustris) was also found to feed primarily on Daphnia (in this case Daphnia hyalina Leydig) during the summer months (Berg and Grimaldi 1966). However, from autumn to spring, the diet was found to consist almost entirely of copepods. While evidence of piscivory has been noted for Italian lacustrine shad and anadromous Irish 98

7 BIOLOGY, ECOLOGY AND FUTURE CONSERVATIONS twaite shad, dietary analysis found no fish eaten by Killarney shad (O Maoiléidigh 1990). Nevertheless, anglers using small spinning lures often catch Killarney shad. THE CURRENT STATUS, PERCEIVED THREATS AND CONSERVATION OF SHAD IN IRELAND During the first half of the twentieth century, twaite and allis shad were the main commercial riverine clupeids in Europe, with high catches, greater than 100 metric tons, in the North and Baltic Sea basins. Nowadays they have declined or disappeared from many areas of Europe (Assis 1990; Bervoets et al. 1990; Maitland and Lyle 1990; Alexandrio 1996; Nicola et al. 1996; Elvira et al. 1998; Aprahamian et al. 2003). The general decline of the shads throughout their European range has been attributed to overfishing in estuaries, obstruction of river migration and habitat destruction by pollution and engineering works. In Portugal, Assis (1990) recommended remedial actions for twaite and allis shad on the River Tagus, such as promotion of detailed studies of the bioecology of the migrant populations under threat, reduction of pollution levels, maintenance of functional and efficient fishways, protection (full and partial) of the spawning grounds, creation of closed fishing seasons and recognition of the need to establish fish hatcheries for restocking purposes. In Ireland, twaite and allis shad are not, like many other rare and endangered fish species, protected under any specific national legislation. Such legislation is largely aimed at the conservation of fish as an exploitable resource rather than as an element of the native fauna (Doherty and McCarthy 2004). Whilde (1993) designated twaite Table 2*/Infection parameters of each parasite species recorded from samples of twaite and allis shad sampled from the River Barrow and Waterford Estuary (Doherty and McCarthy 2001). The intermediate host of each parasite species is also indicated where applicable. Parasite species Authority Intermediate host Spawning freshwater twaite shad (n /60) Post-spawned estuarine twaite shad (n/6) Allis shad (n /12) Abundance Abundance Abundance Monogenea Mazocraes alosae Hermann Direct lifecycle Digenea Pronoprymna ventricosa Rudolphii Amphipods Diplostomum gasterostei Williams Bivalves, molluscs, gastropods Diplostomum spathaceum Rudolphii Bivalves, molluscs, gastropods Hemiurus appendiculateus Rudolphii Copepods Nematoda Hysterthylacium osculatum Rudolphii Crutaceans, other fish species Hysterthylacium aduncum Rudolphii Crutaceans, other fish species Cestoda Eubothrium fragile Rudolphii Copepods Absent Crustacea Clavellisa emarginata Kroyer Direct lifecycle

8 BIOLOGY AND ENVIRONMENT shad as vulnerable and the Killarney and allis shad as endangered in the Red Data Book of Irish vertebrates. The incorporation of Alosa populations into the EU Habitats Directive places an obligation on members of the European Union to assess numbers and exploitation of the populations and to designate Special Areas of Conservation (SACs)/ Sites of Community Interest (SCIs) to safeguard populations (Aprahamian et al. 2003). At sea both Alosa alosa and Alosa fallax are coastal in habit and are clumped in aggregations around the major catchments for reproduction (Aprahamian et al. 2003). Twaite and allis shad are occasionally captured by commercial salmon drift-net fishermen during March /July within Waterford Estuary and for the most part are returned unharmed to the estuary. A relatively large annual catch (0.4 tonnes) of twaite shad was reported by Fahy (1982) on the River Slaney in County Wexford. Though adequate information is not available, it appears that the bycatch is not as great in Waterford Estuary (Doherty and McCarthy 2001). In the River Slaney, twaite shad are captured by ring and snap nets, which use smaller mesh sizes (44 /125mm) compared to the drift nets (119 /125mm) used within Waterford Estuary (Fahy 1982; Doherty and McCarthy 2001). In Ireland the capture of either shad species as bycatch by netsmen is not usually reported. Thus the extent of the migrant estuarine twaite and allis shad elsewhere is unknown and the significance of bycatch levels for both species of shad within Irish estuaries and in adjacent coastal waters is difficult to quantify, as no reliable records are kept. However, anecdotal evidence of bycatch from the salmon (Salmo salar L.) drift- and snap-netting fisheries of Waterford Estuary and the Munster Blackwater Table 3*/Stomach content analysis of Killarney shad (n /32) captured in June 1985 (O Maoiléidigh 1990). Food Group No. of food items % occurrence % number Daphnia spp 29, Copepoda Argulus spp Water mites Dipteran pupae Ceratopogonids Shad scales Pupating chironomids indicate that the levels of bycatch are very low (M. Doherty and M. O Keefe, pers. comm.). Threats to the shad species in Ireland are similar to those described for Irish populations of European smelt (Doherty and McCarthy 2004) and include deteriorating water quality and habitat degradation. These threats apply especially to the localised River Barrow twaite shad spawning population and the freshwater population of Killarney shad in Lough Leane. The reversal of long-term nutrient enrichment on Lough Leane is a priority to protect the population of Killarney shad. The presence of excessive filamentous algal growths overlying littoral gravel areas may impede spawning shad or inhibit intragaseous exchange in the developing eggs, and recently hatched juveniles may become enmeshed in the material and may die as a result. The presence of such excessive algal growth as an overlay is due to Lough Leane being moderately eutrophic (Lucey et al. 1999). The clear identification of spawning sites within Lough Leane and the protection of such sites from the effects of possible development works and factors such as declining water quality are priorities to ensure the long-term survival of the Killarney shad. According to de Groot (1990) the possible restocking of the River Rhine with A. fallax was being reviewed. If needed, this same approach could be implemented for the Lough Leane and River Barrow spawning populations of twaite shad. The effects of exotic freshwater fish introductions on native Spanish species have been reported by Elvira and Almodóvar (2001). They reported that competition between exotic and native species was certain to occur, at least to some degree, but that there was little quantitative information about these interactions. Similarly, the effects of exotic freshwater fish introductions in Ireland and the subsequent spread through freshwater catchments are very difficult to determine. Information, education and public awareness are critical components of any effort to prevent the spread of introduced fish species (Elvira and Almodóvar 2001). Three species of fish were numerically predominant in the 1985 and 1986 gill-netting surveys of Lough Leane. These were brown trout Salmo trutta L., Killarney shad and perch, Perca fluviatilis L. (O Maoiléidigh 1990). More recently, cyprinids such as roach, Rutilus rutilus L., and roach/bream hybrids (Abramis brama L.) are known to be present within Lough Leane (D. O Teangeanna, pers. comm.), and these may represent a threat to the planktonivorous population of Killarney shad. Likewise, the competitive effect of introduced non-indigenous freshwater fish species such as roach on endangered fish species such as Arctic char, Salvelinus alpinus L., may be linked to the 100

9 BIOLOGY, ECOLOGY AND FUTURE CONSERVATIONS extinction of some char populations, such as those of Lough Corrib (Doherty and McCarthy 2000). A similar situation may also occur for other endangered Irish freshwater species such as the pollan Coregonus autumnalis Pallas (Harrod et al. 2001), which occurs in Lough Neagh. ACKNOWLEDGEMENTS The assistance of the zoology staff of the National University of Ireland, Galway, the Central Fisheries Board and South-Western Fisheries Board, the Cheekpoint drift-net fishermen and St Mullins anglers is gratefully acknowledged. Details of the specimen twaite shad were provided by the Irish Specimen Fish Committee (ISFC). REFERENCES Alexandrio, P Genetic and morphological differentiation among some Portuguese populations of allis Alosa alosa (L. 1758) and twaite shad Alosa fallax (Lacépède, 1803). Publication Especiale Institute Espana Oceanography 21, 15/24. 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