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

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

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

Long and strong traditions Fisherman catching crayfish in western Sweden 1912 Sweden has 100 000 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

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

In the beginning there where many success stories and everybody was happy 25 Lake Halmsjön (37 ha) Stocking of signal crayfish started in 1970 20 But then. 15 CPUE 10 5 0 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 Year ~ 45kg/ha CPUE > 10cm CPUE < 10cm ~ 0 kg/ha

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 800 700 698 Catch 600 500 400 300 200 356 230 528 499 505 494 276 253 Numbers indicate catch in kg 100 0 19 24 47 17 30 15 1 0,3 0,1 0,2 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 The fishermen were becoming a bit worried for the future!

Total yearly catch in lake Vättern where commercial signal crayfish fishery constitutes 95% of income Tonnes/Year 160 140 120 100 Lake Vättern? 80 60 40 20 0 1994 1996 1998 2000 2002 2004 2006 2008 2010 Fishermen started to worry more!

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

Båven Små sjöar: Utveckling signalkräfta Erken + Erken Båven Hövern Sjögarpesjön Trehörningen Bunn Läen Lake Vättern Lake Hjälmaren Lake Vänern Sjögarpesjön Hövern Bunn Trehörningen Läen 0 55 110 220 Kilometers

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

Gaps of knowledge Recruitment Natural mortality Growth Movement patterns Fisheries statistics

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

72.676 crayfish in the database

Tagging Erken Hjälmaren Vittsjön Lab 2010 898 st 2011 1671 st 144 st 2012 2008 st 210 st

(%) Recaptures 45 40 35 30 Märkta 2010 Märkta 2011 25 20 15 10 5 0 2010 2011 2012 2013

Trends for the crayfish?

Signal crayfish in Lake Vättern Ton 160 140 120 100 80 60 40 Fångst CatchVättern Ansträngning Effort Vättern 1400 1200 1000 800 600 400 20 200 0 0 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 Effort(1000 * trapnghts)

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

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 2003 2005 2006 2007 2008 2009 2010 2011 2012 2013

60 50 40 % 30 20 The length distribution goes towards smaller sizes 2005 2007 2009 2010 2011 2013 10 0 Längd (mm)

Some analyses and modelling

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 0,58 0 2002 2004 2006 2008 2010 2012

Stock assessment method, MSY -Schaefers logistic production model Based on crayfish fisheries statistics from Lake Vättern Fångst (ton) Catch (ton) 160 140 08 120 100 06 07 09 80 60 05? 2010-2011 40 04 20 02 01 03 0 0 500 1000 1500 2000 Effort ansträngning (trapnights (burnätter x 1000) 1000)

And things have not become easier since Catch Fångst (ton) 160 140 08 120 100 07 13 09 80 06 11 10 12 60 40 20 04 02 03 01 05 0 0 500 1000 1500 2000 Ansträngning Effort (burnätter (trapnights 1000) x 1000)

Stock assessment methods for freshwater crayfish? -the Leslie method 7000 6000 Moulting After moult Fångst per CPUE ansträngning 5000 4000 3000 2000 1000 0 Slope Intercept 0 5000 10000 15000 Cumulative Kumulativ catch fångst or Time

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 0,000 0 200 0 4 000 6000 80 00 1000 0 0,0 00 0 5000 10000 15000 2 0000 4 000 60 00 800 0 1000 0 12 000 140 00 0 10 00 20 00 3000 4000 5 000 60 00 0,4 00 0,3 50 0,3 00 0,2 50 0,2 00 0,150 0,100 0,0 50 0,0 00 0 1000 20 00 30 00 40 00 500 0 6000 0,250 0, 40 0 0,300 0,600 0,40 0 0,200 0, 35 0 0, 30 0 0,250 0,500 0,35 0 0,30 0 0,200 0,400 0,150 0, 25 0 0,25 0 0, 20 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, 05 0 0,000 0, 00 0 0 1000 2000 3000 4000 200 0 300 0 4000 5000 600 0 0,300 0,300 0,250 0,250 0,200 0,200 0,100 0,050 0,100 0,05 0 0,000 0,000 0 100 0 2000 3000 4000 0,00 0 0 500 1000 150 0 2000 2500 3000 0 5 00 1000 15 00 200 0 2 500 3 000 35 00 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 0,000 5000 5500 6 000 650 0 7000 7500 8 000 0,150 0,100 0,200 0,100 0,050 0,100 0,050 0,000 0,000 0,000 0 500 1000 1500 20 00 2 500 0 1000 2 000 300 0 400 0 0 5 00 1000 1500 2000 2500 3000 Lake Vättern 0,300 0,200 0,100 0,000 0 5 00 1000 15 00 20 00 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 0,00 0 0 2 000 40 00 6 000 800 0 0 50 100 150 200 2 50 300 3 50 0 500 1000 1500 200 0 0 500 1000 1500 0,00 0 0 5 00 1000 15 00 2000 2 500 0, 70 0 0,4 50 0,400 0,400 0,8 00 0, 60 0 0,4 00 0,350 0,350 0,7 00 0,3 50 0,300 0,300 0,6 00 0, 50 0 0,3 00 0,250 0,250 0,5 00 0, 40 0 0,2 50 0,200 0,200 0,4 00 0, 30 0 0,2 00 0,150 0,150 0,3 00 0,150 0, 20 0 0,100 0,100 0,100 0,2 00 0,100 0,0 50 0,050 0,050 0,100 0, 00 0 0,000 0,0 00 0,000 0,0 00 3 00 500 700 900 110 0 0 5 00 1000 1500 2000 2500 0 50 100 150 200 0 100 200 300 400 500 600 0 200 4 00 6 00 800 1000 Lake Hjälmaren

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

Estimating suitable crayfish habitat with sonar

Hövern

Bottom hardness Hövern

Crayfish catch Bottom hardness Hövern

CPUE 7 6 5 4 3 2 1 0 17 39 54 64 70 77 87 101 123 156 Soft bottom Hard bottom

Crayfish plague

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

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

Fecundity and female size Is bigger always better?

Gaps of knowledge found Recruitment Natural mortality Growth Movement patterns

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).

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).

It is found in lobsters Agnalt A. L. 2008. ICES J. Marine Science

It is found in 4 north American crayfish Corey S 1987. Crustaceana

It is found in Japanese crayfish Cambaroides japonicus Nakata K. & Goshima S. 2004. Aquaculture

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

It is found in signal crayfish in the US Lewis S. 1997. Master thesis.

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

It is still found in Swedish signal crayfish Söderbäck B. 1995. Freshw. Biol.

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

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

Larger females have more eggs in their ovaries 600 500 Ovarian eggs *** No of ovarian eggs 400 300 200 *** Lake Erken Lake Hövern 100 0 70 80 90 100 110 120 130 140 150 Female size and there is no difference between the lakes

But they do not have more pleopodal eggs in spring 500 450 Pleopodal eggs 400 Number of eggs 350 300 250 200 150 NS; p=0.84; r 2 =0.000 100 50 0 70 80 90 100 110 120 130 140 150 Female size

500 450 Lake Erken p<0.001; r 2 =0.76 400 350 Number of eggs 300 250 200 150 Ovarian eggs late autumn 2010 100 50 0 70 80 90 100 110 120 130 140 150 Female size

500 450 Lake Erken p<0.001; r 2 =0.76 400 350 Number of eggs 300 250 200 150 NS Ovarian eggs late autumn 2010 Pleopodal eggs late spring 2010 100 50 0 70 80 90 100 110 120 130 140 150 Female size

500 450 Lake Erken p<0.001; r 2 =0.76 400 Number of eggs 350 300 250 200 150 NS Ovarian eggs late autumn 2010 Pleopodal eggs late spring 2010 Pleopodal eggs late spring 2011 100 50 NS 0 70 80 90 100 110 120 130 140 150 Female size

600 500 Lake Hövern p<0.001; r 2 =0.78 Number of eggs 400 300 200 Ovarian eggs late autumn 2010 100 0 70 80 90 100 110 120 130 140 150 Female size

600 500 Lake Hövern p<0.001; r 2 =0.78 Number of eggs 400 300 200 Ovarian eggs late autumn 2010 Pleopodal eggs late spring 2010 100 NS 0 70 80 90 100 110 120 130 140 150 Female size

600 Lake Hövern p<0.001; r 2 =0.78 500 Number of eggs 400 300 200 p<0.05; r 2 =0.16 Ovarian eggs late autumn 2010 Pleopodal eggs late spring 2010 Pleopodal eggs late spring 2011 100 NS 0 70 80 90 100 110 120 130 140 150 Female size

Larger females lose more eggs Estimated egg loss in relation to size 100 90 p < 0.001; r 2 = 0.10 Estimated egg loss (%) 80 70 60 50 40 30 20 10 0 70 80 90 100 110 120 130 140 150 Female size

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 2,2 70 80 90 100 110 120 130 140 150 Female size

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

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?

So the biggest mothers are not always the best mothers

Thank you for your attention

Questions?