Crayfish in Scotland

1. Crayfish in Scotland Zara Gladman z.gladman.1@research.gla.ac.uk

2. Overview • Crayfish in Scotland • North American signal crayfish • White-clawed crayfish • Research so far: a synopsis • What next?

3. Crayfish in Scotland • Crayfish are naturally absent from Scotland • Two introduced species: • White-clawed crayfish (Austropotamobius pallipes) • North American signal crayfish (Pacifastacus leniusculus)

4. Crayfish in Scotland • Signal crayfish (Pacifastacus leniusculus) • First recorded in the wild in Galloway, southern Scotland in 1995 • Now inhabits ~ 174 km river length (13 catchments) and several standing waters • Serious threat to biodiversity – pressing need for research  ‘Species Action Framework’, 2007

5. Crayfish in Scotland • White-clawed crayfish (Austropotamobius pallipes) • Native to Europe, including England, Wales and Ireland – but not Scotland • Two Scottish populations • Non-native but protected species (Schedule 5 of Wildlife & Countryside Act 1981, Appendix III of Bern Convention, Annexes IIa and Va of EC Habitats Directive and the Nature Conservation (Scotland) Act 2004, IUCN Red List of Threatened Species)

6. Research so far . . . • 1. White-clawed crayfish • Status of Scottish populations • 2. Signal crayfish • Distribution • Movements (radiotracking) • Control (trapping at Loch Ken) • Impact

7. 1. White-clawed crayfish • Two introduced populations • Durness (Thomas, 1992) • Renfrewshire (Maitland, 2001) • Aim: survey both sites to assess the status of these populations

10. Surveys • Trapping • Hand-searching • Night viewing • Electrofishing • Invertebrate sampling

11. Surveys Providing data on: • Distribution • Population structure • Relative density • Stable isotope samples

12. Research so far . . . • 1. White-clawed crayfish • Status of Scottish populations • 2. Signal crayfish • Distribution • Movements • Control • Impact

13. 2. Signal crayfish Distribution • Methods for detecting signal crayfish in riffles – comparative field study Gladman et al. (2010), Aquatic Conserv: Mar. Freshw. Ecosyst.20: 588-594

14. 2. Signal crayfish Movements • Radio-tracking, mark-and-recapture studies

15. 2. Signal crayfish Control • Effects of trapping on crayfish population at Loch Ken, southern Scotland

16. Crayfish crisis 'looming' on loch 2. Signal crayfish • Control

17. 2. Signal crayfish • Control • Summer 2009: Marine Scotland funded an intensive 4-month trapping programme: • Assess the scale of the infestation • Assess the feasibility of control • Opportunity for research: • Effect of intensive trapping on the population • Two mark-and-recapture projects: one before and one after the trapping programme

18. 2. Signal crayfish • Control • Crayfish sampled at 3 sites (transects of 15 creels, 400 m apart) during two sessions: before (May/June) and after (September) the trapping programme

20. 2. Signal crayfish • Control • Summary • Trapping significantly reduced males; effect on females complicated by trap bias/reproductive status  sex ratio increased towards females • Mean size of crayfish reduced • Crayfish capable of significant movements • High densities mean loss to biodiversity likely to be significant

21. 2. Signal crayfish Impact • Signal crayfish: a threat to Atlantic salmon?

22. Signal crayfish: a threat to Atlantic salmon? • Atlantic salmon in Scotland • Valued part of natural heritage • Significant economic importance (salmon and sea trout: £73 million, annually) • Conservation of high priority • Salmon Conservation (Scotland) Act, 2001 • EU Habitats Directive, 1992

23. Signal crayfish: a threat to Atlantic salmon? • Previous research • Reduced recruitment of salmonid fish in English stream (Peay et al., 2009) • No impact on recruitment (Degerman et al., 2007) Circumstances/mechanism(s) behind declines unclear • Signal crayfish outcompete juvenile Atlantic salmon for shelter (Griffiths et al., 2004) • Interactions during other stages of development? • Egg predation? • Salmonid eggs are palatable to signal crayfish (Nyberg & Degerman, 2000) • Eggs buried in redds?

24. Signal crayfish: a threat to Atlantic salmon? Aim: • To investigate the ability of signal crayfish to detect and excavate artificial salmonid redds

25. Signal crayfish: a threat to Atlantic salmon? Preparation: • Indoor stream fed with water from the River Almond • Stream divided into 16 test arenas • Each arena filled with gravel + two pieces of plastic tubing

26. Impact Signal crayfish: a threat to Atlantic salmon? • Ability of crayfish to detect and excavate boxes containing: • Atlantic salmon eggs • Fish (Clupea herengus L.) • Nothing (control) • Boxes buried 5 cm below gravel surface • One adult male signal crayfish added to each arena

27. Signal crayfish: a threat to Atlantic salmon?

28. Signal crayfish: a threat to Atlantic salmon? Three successive trials: • Treatment 1 (eggs) • Treatment 2 (fish) • Treatment 3 (eggs) (+ empty ‘control’ boxes)

29. Signal crayfish: a threat to Atlantic salmon? Observations: • Number/location/dimensions of excavations recorded daily • At the end of each treatment, number of arenas containing: • No excavations • Minor excavations (≤ 2 cm depth) • Major excavations (> 2 cm depth) • Complete excavations (box exposed) . . . in box area (within 5 cm radius) recorded

30. Results: • Treatment 1 (eggs) • After 14 nights . . . . • 1 arena with a minor excavation, 11 arenas with no excavations Empty ‘control’ boxes undisturbed • Treatment 2 (fish) • After one night . . . • 3 arenas with major excavations, 3 arenas with complete excavations • After two nights . . . • Existing excavations deepened, 4 arenas with new excavations • 5 arenas with complete excavations, 5 arenas with major excavations • Treatment 3 (eggs) • After seven nights . . . • No excavations in any arena

31. Number of arenas containing excavations in the box area is significantly linked to bait type (X2Yates = 20.05, p<0.001 )

32. Signal crayfish: a threat to Atlantic salmon? Conclusions: • Signal crayfish could not detect salmon eggs buried at this depth  low risk of predation in the wild? • Vulnerability of redds likely vary according to a range of biotic and abiotic factors: • Egg – stage of development, dead/damaged eggs, density, burial depth; risk to newly hatched alevins? • Crayfish – density, age • Gravel size – burrowing ability/spawn site selection • Impact of egg predation on recruitment should be assessed on a case-by-case basis

33. What next? • Impact of signal crayfish on native biodiversity: • Freshwater pearl mussels (currently) • Stable isotopes analysis: white-clawed crayfish samples • . . . writing up!

34. Thanks to . . . Colin Adams Colin Bean Jo Long Willie Yeomans z.gladman.1@research.gla.ac.uk