Effects of variable and size-selective gill-net fishing on life-history evolution in grayling

1. Effects of variable and size-selective gill-net fishing on life-history evolution in grayling Thrond O Haugen & Leif Asbjørn Vøllestad

2. La a ? — — — ? + Growth Adult survival Growth + — — Size-selective fishing What to expect from size-selective fishing? • In other words: An open question! • When considered trait by trait

3. What to expect from size-selective fishing—a reaction norm perspective • Theoretical studies show that variation in growth-dependent survival affects the shape and posision of maturation reaction norms (e.g. Stearns & Koella 1986) • For any combination of mortality responses to growth, rapid growers are predicted to mature earlier than slow growers • Expect a smaller age-size maturation space with increasing mortality

4. 0.9 b 0.5 0.1 a Size at maturity c |slope|= |-a/b| width = c Age at maturity Increasing mortality Maturation reaction norms and survival

5. The study species

6. Tributary Lake/river Mature Egg 130-140 °D Max age: 28 years Gravel Larvae 130-140 °D 3-8 years Swim-up larvae 2–3 weeks Juvenile Fry During September

7. Osbumagasinet N Os 1954 Aursjøen Hårrtjønn 1920 Ht Aur Norway ØM Øvre Mærrabottvatn 1910 Lesjaskogsvatnet 1880 Les 10 km The study system

8. Microsatellite FST = 0.05–0.21 Juvenile trait QST = 0.00–0.92 Koskinen, Haugen & Primmer (2002), Nature Characteristics of the lakes and the grayling populations

9. 28 + 22 mm 30 + 22 mm 30 + 22 mm 32 mm 28 mm 30 mm 1900 1950 2000 Monofilament nylon nets Multiple mesh-size survey Relaxed size-selective fishery SIntensive size-selective fishery Lesjaskogsvatnet 1903–2000

10. The Objectives • Do grayling (and co-occuring trout) decrease age and size at maturity in systems with intensive size-selective fisheries? • Among-lake level (synchronic data) • Within-lake level (allochronic data) • If so, is this solely due to growth-rate changes/differences resulting from changed/differential fishing pressure?

11. Methods • Multiple mesh-size gill-nets • 12–52 mm for the synchronic data • 6–10 surveys in the 1995–1999 period per lake • 19–52 mm for the allochronic data • 7 surveys • Ageing and back calculation of growth using otoliths • Maturation pattern estimated from multiple logistic regression • Life-table simulations

12. The synchronic data

13. Øvre Mærrabottvatn 25 Hårrtjønn 20 15 10 5 0 -5 0.1 0.9 0.9 -10 0.5 -15 -20 0.1 -25 Relative size (%) -30 30 Aursjøen Osbumagasinet Lesjaskogsvatnet 25 20 15 10 5 0 -5 0.9 -10 0.5 0.9 0.9 -15 0.1 0.5 0.5 -20 0.1 0.1 -25 -30 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12 Age Differential maturation pattern

14. Life-history evolution in response to differential survival Haugen (2000), Oikos;Haugen & Vøllestad (2001), Genetica

15. Convergent evolution Haugen (2002), Submitted

16. 2.8 Fecundity Egg size GSI 2 La Survival Age at maturity 1 Standardized trait value (sd unit) 0 -1 -2 G2 G3 G1 0 100 200 300 Number of gill nets per km2 per year Responses to differential fishing intensities Haugen (2002), Submitted

17. b a Size at maturity |slope|= |a/b| width = Age at maturity Also affects maturation reaction norms Haugen (2000), Oikos

18. Life-table simulations

19. Predictions for Lesjaskogsvatnet Haugen & Vøllestad (2001), Genetica

20. 1927: 28 mm 32 mm 28/30+22 mm 32 mm 30 mm 28 mm 1975: 28+22 mm 1992: 30+22 mm 1985: 30 mm 1982: 30+22 mm Responses to changed fishing regime Haugen & Vøllestad (2001), Genetica

21. Back calculated length (mm) Has growth changed during the 1900s? • Yes, but not as expected according to changes in density • Selection for lowered growth under high fishing pressure Haugen & Vøllestad (2001), Genetica

22. Conclusions • All three data sets supported that the maturation pattern evolved in response to size-selective fisheries • In an adaptive manner • The response was not due to changed or differential growth pattern • Not a plasticity response • In Lesjaskogsvatnet growth changed directly in response to gill-net selection and not indirectly due to density effects

23. That’s all folks!