The Evolution of Bottom Trawling Impact on North Sea Flatfish Populations

Home , Bottom trawling

Adriaan Rijnsdorp, Jan Jaap Poos, Georg Engelhard, Katrien Lescrauwaet

IFF10, St Malo, 12-16 November 2017 Overview

. History of exploitation . Density-dependent processes . Long-term effects of fishing ● Habitats ● Population biology

2 History of exploitation & management

. Data sources ● Fish remains (archaeological excavations)

Ervinck & van Neer Evidence historic fishing (written sources): rij 16Adriaen Coenen (1578) Visboeck

Bennema & Rijnsdorp 2015 Fish Res, 161: 384-399

N Z

Beam trawl fishery along the coast Controversy about use of beam trawls Letter 19 April 1583 to Willem van Oranje

“...Netten met Hout openghestelt...hebbende onderaen hangen wel sestien ofte seventien ponden Loots, met groote steenen daer beneffens, Adverse effects on seafloor .... Deur de gront gaen strijcken, ....denand food kleynen for fishSchol ende Bot vangen, nemende mede uyt den gront op het Aes waer mede de Visch ghevoedt wordt, .... “Overfishing” .... Indien sulcks gecontinueert worde, dat men in korten tijdt ghelijcke Visch niet meer vangen en soudeDepletion” of fish stock

De Groot, 1984 Ocean Management 9: 177-190 Beam trawl fishery in coastal waters (17th – 18th century)

Mesdag: Pinken in de branding Expansion beam trawl fishery (sailing)

sail 1850: ± 200 1890: 2200

motor Steam (since 1890) Changes in catch rate (NL, England)

Bumb boats Netherlands

Smacks England

Posthumus & Rijnsdorp (2016) Reconstructed stock biomass

Rijnsdorp and Millner 1996 ICES JMS 53: 1170-1184 ICES WGNSSK Density-dependent processes

. Juvenile phase ● DD mortality after settlement ● DD reduced growth nursery grounds group -

Mortality: Modin & Phil, 1994. NJSR 32: 331–341 Van der Veer et al.

Residuallength 0 Teal et al., 2008 Growth: Modin & Phil, 1994. NJSR 32: 331–341 Nash & Geffen, 2007. MEPS 344: Teal et al., 2008 MEPS 358: 219-230 Ciotti et al., 2013 MEPS 475: 213-232 Density-dependent processes

. Adult phase Comparison growth rate annuli in otoliths of ● DD-growth? present day samples with Medieval samples

Bolle et al (2004) J. Sea Res. 51: 313-328 Density-dependent processes

. Adult phase ● No dd-efect in reproduction (relative fecundity)

Rijnsdorp et al (2005) Can J Fish Aquat Sci 62: 833-843 12 Changes in maturation reaction norm & maximum body size (Linf)

50 Linf= 90 cm Linf= 40 53 cm Linf= 48 cm

0 Maturation midpoint Age 4 (cm) 4 Age midpoint Maturation 1890 1910 1930 1950 1970 1990 2010 Grift et al. 2003 MEPS; van Walraven et al. 2010 JSeaR Food web effects of bottom trawling

van Denderen PD, van Kooten T, Rijnsdorp AD. 2013 When does fishing lead to more fish? Community consequences of bottom trawl fisheries in demersal food webs. Proc R Soc B 280: 20131883. Trawling effects on food availability 0.4

155 a 0.3

150 0.2 biomas fish to Prey 145 0.1 at standardized length (g) length standardized at

Wt 140

Pleuronectes platessa 0.0 0 2 4 6 8 Trawling intensity (n/year)

15 Hiddink et al. (2016) J Applied Ecol 53: 1500-1510

Long-term effects of trawling

. Phenotypic plasticity ● Density-dependence ● Temperature effects ● Eutrophication ● Trawling effects on food availability . Changes in sea-bed habitats . Evolutionairy changes

16 Fisheries-induced evolution Expectations (modelling evolution of growth, maturation and reproduction) < • Evolving traits: Emergentdw traits3/4 :  0 if ttmat =aw −− bw  a,decrease c, tmatin max sized&t size / age atcw 1stif maturity t≥ tmat ,

Genetic traits

Start exploitation

Mollet et al. (2015) MEPS; Mollet et al. (2016) CJFAS Managing fisheries-induced evolution

Flat-topped exploitation Size at maturationat Size (reaction norm)

Mollet et al. (2016) CJFAS 73: 1126-1137 Managing fisheries-induced evolution Protect large / old fish

Full dome-shaped norm) reaction ( Half dome-shaped maturation Flat-topped exploitation at Size

Mollet et al. (2016) CJFAS 73: 1126-1137 Conclusions

. Population regulation • Importance of nursery phase • Density-dependence in adult growth questionable, but what is happening now SSB is at historic high? Conclusions

• Population regulation • Importance of nursery phase • Density-dependence in adult growth questionable, but what is happening now SSB is at historic high? . Juvenile growth increased due to eutrophication (and perhaps bottom trawling) • affects size and age at maturation (phenotypic plasticity) Conclusions

• Population regulation • Importance of nursery phase • Density-dependence in adult growth questionable, but what is happening now at historic high SBB? • Juvenile growth increased due to eutrophication (and perhaps bottom trawling) • affects size and age at maturation (phenotypic plasticity) . Fisheries-induced evolution • Fisheries selection low until ~ 1880 • Management advise: protect large / old fish Conclusions

• Population regulation • Importance of nursery phase • Density-dependence in adult growth questionable, but what is happening now at historic high SBB? • Juvenile growth increased due to eutrophication (and perhaps bottom trawling) • affects size and age at maturation (phenotypic plasticity) • Fisheries-induced evolution • Fisheries selection low until ~ 1880 • Management advise: protect large / old fish . Change in sea-bed habitats