Signal crayfish latest views from Sweden. Lennart Edsman Institute of Freshwater Research

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1 Signal crayfish latest views from Sweden Lennart Edsman Institute of Freshwater Research

2 Signal crayfish a little of this and some of that Lennart Edsman Institute of Freshwater Research

3 Long and strong traditions Fisherman catching crayfish in western Sweden 1912 Sweden has lakes >1 ha In principle the fishing right belongs to owner In the 5 largest lakes state controlled fisheries North American signal crayfish was introduced in 1960ies to improve the fishery Swedes consume 4.5 million kg of crayfish yearly

4 Noble crayfish (the original) Signal crayfish (the substitute) The native noble crayfish (Astacus astacus) was classified as critically endangered in the national red list year 2010, since 97% of the populations has disappeared in the last 100 years mainly due to the disease crayfish plague. The extinction rate has accelerated lately. The north American signal crayfish (Pacifastacus leniusculus) was introduced into waters in Sweden starting in the 1970ies to substitute for the noble crayfish fishery lost and to give a more reliable catch. More than 4000 permits given. Turned out to be a chronic carrier of crayfish plague. Large unfounded expectations. Collapses. Has been a disaster for the noble crayfish

5 In the beginning there where many success stories and everybody was happy 25 Lake Halmsjön (37 ha) Stocking of signal crayfish started in But then. 15 CPUE Year ~ 45kg/ha CPUE > 10cm CPUE < 10cm ~ 0 kg/ha

6 So the signal crayfish catch is not always increasing indefinitely. There have been many examples of strong declines Signal crayfish catch by one commercial fisherman in Lake Mälaren Catch Numbers indicate catch in kg ,3 0,1 0, The fishermen were becoming a bit worried for the future!

7 Total yearly catch in lake Vättern where commercial signal crayfish fishery constitutes 95% of income Tonnes/Year Lake Vättern? Fishermen started to worry more!

8 How to achieve and manage a sustainable fishery of signal crayfish L. Edsman, A. Sandström, F. Engdahl, M. Ågren, M. Andersson, A. Asp, P. Bohman, A. Fjälling, P. Nyström, K. Olsson, M. Stenberg Swedish University of Agricultural Sciences, Institute of Freshwater Research and Ekoll AB, Sweden

9 Båven Små sjöar: Utveckling signalkräfta Erken + Erken Båven Hövern Sjögarpesjön Trehörningen Bunn Läen Lake Vättern Lake Hjälmaren Lake Vänern Sjögarpesjön Hövern Bunn Trehörningen Läen Kilometers

10 The commercial signal crayfish fishery is the second most economically important inland in Sweden The joint project managers-fishermen-scientist started in 2009 in order to Study stock status and impact of the fisheries Analyse and model population dynamics Utveckling signalkräfta: fältarbetet Investigate reasons for collapses in signal crayfish populations Deliver advice and guidelines to fishermen, managers and authorities First we did a literature survey to find gaps of knowledge

11 Gaps of knowledge Recruitment Natural mortality Growth Movement patterns Fisheries statistics

12 Sampling catch Monitoring Every year 2 sampling fishermens catch 1 standardised test fishing We recorded size, moulting stage, injuries, diseases

13 crayfish in the database

14 Tagging Erken Hjälmaren Vittsjön Lab st st 144 st st 210 st

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16 (%) Recaptures Märkta 2010 Märkta

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21 Trends for the crayfish?

22 Signal crayfish in Lake Vättern Ton Fångst CatchVättern Ansträngning Effort Vättern Effort(1000 * trapnghts)

23 0,350 The average catch in August has decreased Kg per trapnight 0,300 0,250 0,200 0,150 0,100 0,050 0,000

24 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0 There are fewer large crayfish F/A < 10 cm CPUE < 10 cm CPUE > 10 cm

25 % The length distribution goes towards smaller sizes Längd (mm)

26 Some analyses and modelling

27 Communal fishing area in Lake Vättern high effort 4 3,5 Total mortality 3 2,5 2,63 Z +- CI 2 1,5 1,89 1,9 1 0,5 0,56 0,68 0,

28 Stock assessment method, MSY -Schaefers logistic production model Based on crayfish fisheries statistics from Lake Vättern Fångst (ton) Catch (ton) ? Effort ansträngning (trapnights (burnätter x 1000) 1000)

29 And things have not become easier since Catch Fångst (ton) Ansträngning Effort (burnätter (trapnights 1000) x 1000)

30 Stock assessment methods for freshwater crayfish? -the Leslie method Moulting After moult Fångst per CPUE ansträngning Slope Intercept Cumulative Kumulativ catch fångst or Time

31 0,000 Leslie method applied to individual fisheries 0,450 0,400 0,350 0,300 0,250 0,200 0,150 0,100 0,050 0,400 0,350 0,3 00 0,350 0,300 0,2 50 0,300 0,250 0,2 00 0,250 0,200 0,200 0,150 0,150 0,150 0,100 0,100 0,100 0,050 0,0 50 0,050 0,000 0, , ,4 00 0,3 50 0,3 00 0,2 50 0,2 00 0,150 0,100 0,0 50 0, ,250 0, ,300 0,600 0,40 0 0,200 0, , ,250 0,500 0,35 0 0,30 0 0,200 0,400 0,150 0, ,25 0 0, , 150 0,300 0,20 0 0,100 0,150 0, 100 0,200 0,150 Fishermen fishing only in communal areas 0,100 0,050 0, ,000 0, ,300 0,300 0,250 0,250 0,200 0,200 0,100 0,050 0,100 0,05 0 0,000 0, , ,350 0,700 0,600 0,300 0,600 0,500 0,250 0,500 0,400 0,200 0,400 0,150 0,150 0,300 Fishermen fishing in there own area 0,100 0,050 0, ,150 0,100 0,200 0,100 0,050 0,100 0,050 0,000 0,000 0, Lake Vättern 0,300 0,200 0,100 0, Fishermen fishing anywhere 0,25 0 0,50 0 0,45 0 0,45 0 0,40 0 1,000 0,90 0 0,40 0 0,35 0 0,20 0 0,40 0 0,35 0 0,80 0 0,30 0 0,35 0 0,30 0 0,70 0 0,150 0,30 0 0,25 0 0,60 0 0,25 0 0,25 0 0,50 0 0,20 0 0,100 0,20 0 0,20 0 0,40 0 0,150 0,05 0 0,150 0,100 0,150 0,100 0,30 0 0,20 0 0,100 0,05 0 0,05 0 0,100 0,05 0 0,00 0 0,00 0 0,00 0 0, , , ,4 50 0,400 0,400 0,8 00 0, ,4 00 0,350 0,350 0,7 00 0,3 50 0,300 0,300 0,6 00 0, ,3 00 0,250 0,250 0,5 00 0, ,2 50 0,200 0,200 0,4 00 0, ,2 00 0,150 0,150 0,3 00 0,150 0, ,100 0,100 0,100 0,2 00 0,100 0,0 50 0,050 0,050 0,100 0, ,000 0,0 00 0,000 0, Lake Hjälmaren

32 Other things we did in connection Stable isotopes to study food webs Age determination - Lipofuscin Genetics Reasons for declining catches Crayfish plague detection in natural waters with Real time PCR

33 Estimating suitable crayfish habitat with sonar

34 Hövern

35 Bottom hardness Hövern

36 Crayfish catch Bottom hardness Hövern

37 CPUE Soft bottom Hard bottom

38 Crayfish plague

39 Percentage crayfish with visible black plague spots 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%

40 Percentage with crayfish plague 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Synliga Visiblepestfläckar spots Pest Crayfish enligt plague analysanalysed

41 Fecundity and female size Is bigger always better?

42 Gaps of knowledge found Recruitment Natural mortality Growth Movement patterns

43 Recruitment is important! Recruitment is crucial for variation in catch and dynamics of fished stocks. (Hjort, 1914; Beverton & Holt 1957; Houde, 1987) Recruitment and particularly the relationship between fecundity by female size/age and spawning biomass/egg number per recruit is an important element in many attempts to model population dynamics of exploited crustaceans (Beverton & Holt, 1957; Smith & Addison 2003; Sadykova et al. 2009; Sadykova et al. 2011).

44 Already Darwin.. "Increased size must be in some manner of more importance to the females... and this perhaps is to allow the production of a vast number of ova" (Darwin 1874).

45 It is found in lobsters Agnalt A. L ICES J. Marine Science

46 It is found in 4 north American crayfish Corey S Crustaceana

47 It is found in Japanese crayfish Cambaroides japonicus Nakata K. & Goshima S Aquaculture

48 It is found in crayfish in Scandinavia Skurdal & Taugbøl, 1994

49 It is found in signal crayfish in the US Lewis S Master thesis.

50 It was found in signal crayfish in Sweden Abrahamsson 1971, OIKOS

51 It is still found in Swedish signal crayfish Söderbäck B Freshw. Biol.

52 Summing up expectations ovarian and pleopodal egg numbers are believed to increase linearly with female size

53 What we did Ovarian egg counts in late autumn in the two lakes 2010 Pleopodal egg counts in late spring 2010 and 2011 Egg size/diameter measured

54 Larger females have more eggs in their ovaries Ovarian eggs *** No of ovarian eggs *** Lake Erken Lake Hövern Female size and there is no difference between the lakes

55 But they do not have more pleopodal eggs in spring Pleopodal eggs 400 Number of eggs NS; p=0.84; r 2 = Female size

56 Lake Erken p<0.001; r 2 = Number of eggs Ovarian eggs late autumn Female size

57 Lake Erken p<0.001; r 2 = Number of eggs NS Ovarian eggs late autumn 2010 Pleopodal eggs late spring Female size

58 Lake Erken p<0.001; r 2 = Number of eggs NS Ovarian eggs late autumn 2010 Pleopodal eggs late spring 2010 Pleopodal eggs late spring NS Female size

59 Lake Hövern p<0.001; r 2 =0.78 Number of eggs Ovarian eggs late autumn Female size

60 Lake Hövern p<0.001; r 2 =0.78 Number of eggs Ovarian eggs late autumn 2010 Pleopodal eggs late spring NS Female size

61 600 Lake Hövern p<0.001; r 2 = Number of eggs p<0.05; r 2 =0.16 Ovarian eggs late autumn 2010 Pleopodal eggs late spring 2010 Pleopodal eggs late spring NS Female size

62 Larger females lose more eggs Estimated egg loss in relation to size p < 0.001; r 2 = 0.10 Estimated egg loss (%) Female size

63 This may compensate a bit - assuming that large eggs give large hatchlings, where large size is a competitive advantage 3,2 Egg size in relation to female size 3 p < 0.05; r 2 = 0.09 Egg size 2,8 2,6 2,4 2, Female size

64 Conclusions Larger female crayfish were thought to contribute more to future recruitment by higher fecundity We did not always find that Anyway not for signal crayfish.. and not in Sweden We do not know why! Relationship between ovarian egg numbers and female size should be used with care when modelling crayfish population dynamics

65 Pure speculation! What makes large females lose more of their eggs? Susceptibility to disease increases with age or number of reproductive events? Senescence in old/large individuals? Lazy? Behavioural difference between sizes leading to more stress?

66 So the biggest mothers are not always the best mothers

67 Thank you for your attention

68 Questions?