Modelling from experiments on farm and wild Atlantic salmon in nature Kjetil Hindar & Ola Diserud Norwegian Institute for Nature Research (NINA), Trondheim, Norway Phil McGinnity, Marine Institute, Ireland Ian Fleming, Ocean Sciences Centre, Nfld., Canada Genimpact, Bergen, July 2007

Background: wild and farm salmon  Atlantic salmon is a highly valued species  Population sizes in nature may be at an all- time low  Farm salmon production is increasing  Escaped farm salmon outnumber wild salmon in several rivers.  What are the long-term consequences?  Implications for management?

Wild Atlantic salmon (Salmo salar)  Consist of many semi-isolated populations in nature  Show between-population variation in molecular and quantitative genetic traits  Some differences likely represent local adaptation

Cultured Atlantic salmon  Outnumber wild salmon 500-fold  – fish escape every year  Make up 20-40% in North Atlantic catches of salmon  Constitute ca. 20% in Norwegian rivers at spawning  Are increasingly genetically different from wild fish

Modelling interactions  Look at the long-term consequences using: Population vectors from surveys in Norwegian rivers Spawning success and survival vectors from experiments Input parameter values varied across likely range (Hindar et al., 2006 ICES J Mar. Sci., 63)

Farm and wild salmon in R. Imsa (Fleming et al., 2000 Proc. R. Soc. Lond. B, 267)  One generation: adult-to- adult in a controlled natural stream  22 farm and 18 native spawners released  16% farm success vs. native salmon  ca. 30% lower total and native smolt productivity

Farm and wild salmon in Burrishoole (McGinnity et al., 2003 Proc. R. Soc. Lond. B, 270)  Two generations: egg-to-adult  Farm salmon had lifetime success of 2-4% relative to Wild  ‘Hybrids’ showed intermediate fitness and decreased survival; by rank: Backcross to wild, 89% FxW hybrid (wild mother) 2nd generation hybrid Backcross to farm WxF hybrid (farm mother)27%

Spawning success Fish typeRelative successReference Sea-ranched male0.51 ( )1 Sea-ranched female0.91 ( )1; 2 Farm male0.13 ( ) 3; 4 Farm female0.44 ( )2; 3; 4 1 Fleming et al. (1997) Behav. Ecol., 8 2 H. Lura (1995) PhD thesis, University of Bergen 3 Fleming et al. (1996) J. appl. Ecol., 33 4 Fleming et al. (2000) Proc. R. Soc. Lond B, 267

Spawning success: parr males Fish typeProportional successReference (% of eggs) Wild X wild 4.5 ( )1; 2 Wild X farm10.5 ( )1; 2 Farm X farm 8.5 ( )1; 2 1 Garant et al., (2003) Ecol. Letters, 6 2 Weir et al., (2005) Can. J. Fish. Aquat. Sci., 62 In total; parr males fertilised 23-24% of the eggs in the two experiments. Larger variation is known.

Survival (Fleming et al., 2000; McGinnity et al., 2003) Fish typeEgg to to smoltSmolt to adult Wild X wild111 Farm X wild; W X F0.67 ( )0.92 ( )0.85 ( ) Farm X farm0.88 ( )1.06 ( )0.33 ( ) Backcross to W Backcross to F nd gen hybrid NA

Basic simulation (Hindar et al., ICES J. Marine Sci., 63)  20% farm escapes each generation  Even sex ratio  Average fitness from experiments  No mature parr  Back-crosses to ’1/2 wild or farm’ and ’1/2 hybrid’  4-yr generation wild hybrid feral farm

Difference between rivers wild hybrid feral farm wild hybrid River Stjørdalselva, consecutive intrusion rates: [0, 0.07, 0, 0.02, 0, 0, 0, 0.25, 0, 0, 0.03, 0.03] River Vosso, [0, 0.19, 0.23, 0.46, 0.75, 0.61, 0.71, 0.59, 0.65, 0, 0, 0] Hindar et al., (2006) ICES JMS, 63

Recovery of high-impacted populations?  ’High’ for 10 years. Then no escapes for 100 years W H W H FF Years Proportions

Other effects (not modelled)  Higher growth rate of farm and hybrid offspring  Altered life-history traits Age at smoltification Age at sexual maturity  Reduced productivity: 30% fewer smolts  Increased interspecific hybridisation with trout  Diseases

Can we suggest limits to gene flow? Some possibilities to consider:  Intrusion rate (x modelled fitness)  Genetic difference between populations  Long-term effective population size

Intrusion rate of escaped farm salmon: results after 10 generations W H W FF Proportion escaped farm salmon Proportion wild hybrid feral farm

Genetic difference between populations  Do not allow more migrants than can be deduced from F ST = 1 / (4N e m + 1)  Limit related to difference between donor and recipient, which can be estimated by genetic analysis  F ST ~ 0.05 between rivers within continent (N e m ~ 5)  F ST > 0.25 between continents (N e m < 1)  Wild vs captive somewhere between (N e m ~ 2) Ryman (1991) J. Fish Biol., 27 (suppl A) Alternative based on quantitative trait: Tufto (2001) Amer. Natur., 158

Long-term effective population size (Tufto & Hindar, J. theor. Biol., 222) Two-way symmetric gene flow One-way gene flow * isolation increases total effective population size * asymmetry in gene flow decreases total effective population size Two-way asymmetric gene flow

Summary & recommendations  Farm escaped salmon have negative effects on wild salmon Effects cumulative over generations Population eventually composed of ‘hybrids’ and feral farm fish  Farm fish must be contained By keeping them inside the net pens By sterilization