MONITORING PROGRAMME OF WHITE-CLAWED CRAYFISH IN IRISH LAKES - NPWS Training Talk Dr. William O Connor
Lifecycle, ecology and distribution of crayfish in Ireland
Crayfish are large, mobile freshwater invertebrates Introduction Considered keystone species wherever they occur The white-clawed crayfish (Austropotamobius pallipes) is Ireland s only crayfish species.
Natural range in Europe dramatically reduced in the last 150 years Irish stocks of substantial conservation importance. Human disturbances such as overfishing, habitat destruction, pollution, disease and the introduction of foreign crayfish species
European and Irish legislation Protection Wildlife Act, 1976 classified as vulnerable in the IUCN Red List Appendix III of the Bern Convention Annexes II and V of the EU Habitats Directive.
Slow growing compared to other astacids Life Cycle Reach 9cm total length in five or more years (max 12cm) Can live for more than 10 years Sexual maturity after three to four years Grow by moulting their shell and increasing by about 10% in length before the new one hardens. Immature crayfish may moult several times each year Mature males usually moult twice, early and late summer while reproductive females only once, in late summer.
Males can be distinguished from females by the specialised first two pairs of appendages on the undersides of the abdomen. These appendages function like a plunger to introduce a white spermatophore onto the underside of the female during mating. Adult males have larger claws than females and are more territorial, especially in the mating season. Females develop a broader abdomen, which accommodates the brood.
Mating occurs in October to November at a water temperature of around 10ºC. The females abdominal appendages are more hairy than those of the male and are used to support the mass of eggs, which is glued to them after laying, the number of eggs carried may range from 20 to 160, but is usually less than 100.
Life Cycle (continued) Such females are described as berried some females may lose most or all of their eggs while others will carry the majority to full term until about June. The hatchlings (8mm) remain attached to the mother until their second moult when they become independent, the female can then resume feeding and moult. The presence of juveniles would indicate a healthy breeding population of white-clawed crayfish.
Distribution in Ireland White-clawed crayfish are still widespread in the Irish midlands, where the geology is predominantly limestone. The distribution of white-clawed crayfish has declined since the mid-1980s Due in part to crayfish plague caused by the fungus Aphanomyces astaci. Crayfish populations in the lakes and rivers of the Boyne catchment are thought to have been decimated by crayfish plague.
Habitat Found in rivers and lakes Can tolerate slightly polluted conditions Require relatively hard water with high calcium levels Require plenty of refugia such as boulders, rocks ad cobbles, tree roots, vegetation etc. Juveniles are typically found among weed and debris in shallow water.
Food and Predators In Irish lakes the white-clawed crayfish prey on a wide variety of benthic invertebrates including snails, crustaceans and insect larvae. The grazing impacts of crayfish on aquatic macrophytes have long been known, their grazing checks primary productivity and in their absence luxuriant macrophyte growth may occur. Predators include dragon fly nymphs (juvenile crayfish), herons, salmonids, eels, perch, pike, otters.
Threats Environmental: habitat loss, water quality deterioration. Biotic: Predation, competition, disease.
Monitoring of Crayfish in Lakes
The Habitats Directive requires the condition of the habitats and species for which an SAC has been designated to be monitored An assessment of favourable conservation status Standard monitoring methods, assessment and reporting to allow results to be both compared and aggregated within and across EU member states. Assessment techniques for data collection at habitat and species level not available
Timing and conditions Crayfish are most active between June and November, and are best surveyed in summer or autumn. Avoid periods of high water, winds and heavy rain. Distribution of crayfish may not be homogeneous within a lake. Larger crayfish prefer stony shores, but access may determine which sites are available to survey. Monitoring is easiest on gently sloping stony shores facing prevailing winds, as these are relatively free from mud and provide ample refuges for crayfish. It is important to select the best possible sites.
Survey methods For logistical reasons, work in pairs. Follow at least one of the following methods: hand search, sweepnetting, night search, trapping. Two or more methods will give some relative measures. Night search and trapping will chiefly locate larger crayfish, while hand search and sweep-netting methods may find both juveniles and adults. For all methods you will need a digital camera, GPS hand-set, notebook, buckets or containers for crayfish caught, and measuring callipers. Check each method for any additional equipment needed. Make biological and other observations after sampling each patch.
Check access and examine the available substrate. On arrival at the lake Estimate the extent of most suitable habitat. Look for surrogate information cast shells, remains in otter spraints, burrows etc. Where vertical banks are visible, look for burrows with flattened oval entrances about 5-10 cm across. Take digital photos and GPS readings for sites where crayfish are particularly abundant, or where patches are widely spaced along the shore, to facilitate repeatability. Make biological observations on the crayfish catch from each defined sample (patch, sweep or trap) separately.
Habitat definitions Stretch: a lake margin with apparently suitable substrate. There may be several stretches of different extent at any one lake Patch: within a stretch, an area containing a concentration of refuges, or an otherwise defined area, e.g. that covered by a standard sweep, or an area of shoreline illuminated by torchlight for night search. Refuge: a stone, crevice or clump of weed which may shelter crayfish.
Biological Sampling As each patch, sweep or trap is surveyed, place any captured crayfish in a bucket with lake water. Record total length (TL) (excluding claws) and hard carapace length (CL) Juvenile (16-50 mm TL) or adult (greater than 50 mm TL), Male or female, breeding status Note also any signs of damage or disease, then return specimen to place of capture before moving on to sample the next patch. If a crayfish is seen but not caught, estimate its size and stage as hatchling, juvenile or adult. Record all data in a notebook. At the end of sampling, upload the data onto the attached Recording Form, including notes on breeding and disease status etc. under Other comments.
Measuring and handling
Recording survey details Basic survey details, including conditions at the time of survey. Habitat details in each habitat patch. An overall appraisal of habitat for crayfish and ease of survey in the site. Crayfish record, the details of the catch.
Health and Safety
Hand-searching This method is most suitable for lakes with abundant stony cobble in the shallows. Aim to examine at least 100 m of shoreline, depending on lake size. Estimate how many stretches of this habitat are available in the lake, and accessible to surveyors.
Centre the stretches on known crayfish hotspots where possible. Select 10 patches of stones in each stretch and ideally investigate 10 refuges per patch. If stony stretches are continuous, treat the whole lake shore as a stretch and define patches at a suitable distance apart. If crayfish are found in abundance, concentrate on just one stretch per lake.
Night search If the edge shelves abruptly, or the bottom is soft marl or mud which may swirl up if disturbed and obscure vision, consider night viewing as an alternative. An estimate of margin length and width viewed in each area and a count of animals seen will give a semi-quantitative abundance of crayfish moving around in the area. Weed and algal growth may limit usefulness of this method. Safety considerations
Sweep netting If there are no or few stones, or the bottom is obscured by weed, algae or debris, use a hand-held pond net, treating one standard sweep of the net as a sampling unit. Select an apparently favourable area as the patch to be sampled. Hand-searching and sweep-netting are not directly comparable. As sweeps are less predictable than hand search, therefore, aim to do a minimum of 20 sweeps per lake.
Trapping Trapping should be considered where the terrain is unsuitable for hand search, sweep-netting or night search. Baited traps may attract crayfish from an unknown area, probably several square metres. Set the baited traps before dusk, and retrieve them early the following day.
Experimental method Dependant on conductivity Low and variable efficiency Currently being evaluated Electrical fishing
Analysis of crayfish catch Crayfish abundance per site, as no. crayfish per 10 refuges Size distribution of population. Percentage of population as juveniles less than 25 mm carapace length (CL). Health of population Percentage of adult females showing signs of breeding.
Preliminary results from the current survey
No Lakes Catchment County 1 Lough Doon Bonet Leitrim 2 Lough Gill Sligo 3 Lough Glenade Leitrim 4 Lough Labe Sligo 5 Lough Kill Boyne Cavan 6 Lough Major Monaghan 7 Lough Tullaghan Monaghan 8 White Lake Meath 9 Lough Aclaureen Corrib Roscommon 10 Lough Carra Mayo 11 Lough Corrib Galway 12 Lough Mask Mayo 13 Loughaunwillian Galway 14 Lough Carrickaport Erne Leitrim 15 Lough Glaslough Monaghan 16 Lough Gowna Cavan 17 Lough Kilrooskey Monaghan 18 Lough Nageage Donegal 19 Lough Veenagrane Donegal 20 Poulaphuca Reservoir Liffey Wicklow 21 Lough Talt Moy Sligo 22 Lough Carrickacladdy Shannon Leitrim 23 Lough Derg Tipperary 24 Lough Ennell Westmeath 25 Lough Owel Westmeath 26 Lough Ree Westmeath
The largest lake surveyed was Lough Corrib No crayfish recorded at three sites investigated. Also not found at sites investigated in Loughs Mask and Carra.
The smallest lake surveyed was Lough Tullaghan, Co Fermanagh, which appeared to have good water quality No crayfish recorded
Lough Labe (Sligo) is a small upland lake with ideal habitat. Sampled by hand searching and sweep netting. N=21 crayfish were caught in the 100 refuges searched.
Loughaunwillian, Co Galway was the most westerly lake surveyed. It has a history of pollution and no crayfish were found here.
Poulaphuca Reservoir, this man made reservoir in County Wicklow was the most easterly lake surveyed. Moderate numbers of crayfish recorded. High water levels at time of survey. To be resurveyed.
Suitable habitats present at Lough Carrigacladdy, Co. Cavan. No crayfish were caught here. Will be resurveyed in September.
Lough Nageage, Co. Donegal was a small upland lake, heavily vegetated and soft substrate. No Crayfish recorded. Plan to resurvey in September with traps. Crayfish present in nearby Lough Veenagreane. This lake had a shallow rocky shore.
Good numbers in Lough Owel Absent in nearby Lough Ennell.
A total of 52 crayfish were recorded at two sites (200 refuges) on Lough Talt, Co. Sligo.
Nominal population in White Lake, Co Westmeath Large population here in the 1980 s Crayfish plague outbreak Restocked by NPWS
Crayfish have been confirmed present in 10 of the 25 lakes surveyed to date. Summer 2007 was very wet and lake levels were high. Selection of lakes will be resurveyed in September 2007.
No Lakes Catchment County Crayfish Present 1 Lough Doon Bonet Leitrim YES 2 Lough Gill Sligo 3 Lough Glenade Leitrim YES 4 Lough Labe Sligo YES 5 Lough Kill Boyne Cavan 6 Lough Major Monaghan 7 Lough Tullaghan Monaghan 8 White Lake Meath YES 9 Lough Aclaureen Corrib Roscommon To be surveyed 10 Lough Carra Mayo 11 Lough Corrib Galway 12 Lough Mask Mayo 13 Loughaunwillian Galway 14 Lough Carrickaport Erne Leitrim 15 Lough Glaslough Monaghan 16 Lough Gowna Cavan YES 17 Lough Kilrooskey Monaghan YES 18 Lough Nageage Donegal 19 Lough Veenagrane Donegal YES 20 Poulaphuca Reservoir Liffey Wicklow YES 21 Lough Talt Moy Sligo YES 22 Lough Carrickacladdy Shannon Leitrim 23 Lough Derg Tipperary 24 Lough Ennell Westmeath 25 Lough Owel Westmeath YES 26 Lough Ree Westmeath
Today s demonstration Demonstration of hand search method (snorkelling) Crayfish handling, sexing and measuring. Sweep net method.