Farming of Atlantic cod Gadus morhua in the vicinity of major spawning sites for Norwegian coastal cod populations - is it hazardous? Svein-Erik Fevolden 1 , Jon-Ivar Westgaard 2 , Jørgen Schou Christiansen 1 1) University of Tromsø, Faculty of Biosciences, Fisheries and Economics, 9037 Tromsø, Norway 2) Institute of Marine Research, 9294 Tromsø, Norway Waters along and adjacent to the coast of northern Norway are unique in housing two major populations of Atlantic cod with very different life histories. The Northeast Arctic cod (NEAC) has its nursery and feeding grounds in the Barents Sea but migrates to the coast of northern Norway to spawn. Norwegian coastal cod (NCC) is more stationary, spawns mainly at local sites in individual ords but to some degree also overlap with the spawning sites of NEAC (Fig.1). These distinctive patterns in life history are reflected in a clear-cut genetic divergence between the two populations. Various molecular genetic markers (scnDNA, microsatellites and SNPs) have displayed genetic differences between NEAC and NCC which are remarkable for marine fish with a comparable gene flow potential (cf. Sarvas and Fevolden 2005, Wennevik et al. 2008, and Westgaard and Fevolden 2008 for recent updates). The unique biology and genetic make-up of the two cod populations needs to be taken into consideration when design- ing a management regime for cod farming in northern Norway. In contrast to captive Atlantic salmon, the iteroparous and batch spawning Atlantic cod may spawn over extended periods allowing escapement of the pelagic eggs and larvae in addition to adults (Jørstad et al. 2008). Thus, strict criteria should be set on the choice of brood stocks, using preferably native populations, and avoid producing hybrids between NEAC and NCC despite potential production advantages they might have. The list of reservations against an impetuous development in cod farming is extensive and should be founded entirely on the unique characteristics of the natural cod populations of concern. Jørstad KE, van der Meeren T, Paulsen OI, Thomsen T, Thorsen A, Svåsand T (2008) “Escapes” of eggs from farmed cod spawning in net pens: recruitment to wild stocks. Reviews in Fisheries Science 16: 285-295. Nielsen EE, Bach LA, Kotlicki P (2006) HYBRIDLAB (version 1.0): a program for generat- ing simulated hybrids from population samples. Molecular Ecology Notes 6: 971-973. Sarvas TH, Fevolden S-E (2005) Pantophysin (Pan I) locus divergence between inshore v. offshore and northern v. southern populations of Atlantic cod in the north-east Atlantic. Journal of Fish Biology 67 (2): 444-469. Westgaard JI, Fevolden S-E (2007) Atlantic cod (Gadus morhua L.) in inner and outer coastal zones of northern Norway display divergent genetic signature at non-neutral loci. Fisheries Reearch. 85: 320-329. Wennevik V, Jørstad KE, Dahle G, Fevolden S-E (2008) Mixed stock analysis and the power of different classes of molecular markers in discriminating coastal and oceanic Atlantic cod (Gadus morhua L.) on the Lofoten spawning grounds, Northern Norway. Hydrobiologia 606(1): 7-25. By means of the software Hybridlab 1.0 (Nielsen et al. 2006) we simulated the effect of introgression between farmed NEAC and the native NCC population. The simulations were carried out with 1, 5, 10, and 25 % introgression of genetic material from NEAC. Given the high numbers of fish in a single cod farm and the notorious Houdini- talent of captive cod, the introgression levels employed here are deemed realistic for many northern Norwegian ords designated for cod farming. Figure 2 visualizes the effect on allele frequency distribution of the least common allele in native NCC by various levels of introgression from farmed NEAC. The Pan I exhibits the highest effect of introgression by escapees, in accordance with its displaying the largest divergence (F ST ) be- tween the farmed and native population. The GM240_0209 locus displays the highest divergence and most profound effect among the SNP loci. Figure 3 shows the effect on F IS for each locus in the native population by introgression from farmed NEAC. For Pan I and GM240_0209, F IS becomes increasingly negative by higher introgression rates, that is, the population deviates more and more from Hardy-Weinberg expecta- tions due to excess of heterozygotes, a typical hybridization effect. Given farmed escaped and wild cod interbreed, a simple simulation study on the genetic effects of escapees on a native ord population is outlined by consid- ering farming of typical North East Arctic cod (NEAC) in a ord known to be a spawning site for Norwegian coastal cod (NCC). Thus, two genetically known sam- ples from wild cod populations were used, NEAC sampled off Bear Island (Barents Sea) and NCC from the inner part of Ullsord (Troms County). Five molecular markers were included in the simulation study. They were four SNPs, all showing high adaptive divergence between NEAC and NCC, with FST values from 0.20 to 0.47 between the two populations. In addition, we analysed the Pan I locus (in re- ality also a SNP), which displays extreme allele frequency differences between NEAC and NCC (F ST = 0.71). Introduction Concern for cod farming Simulated genetic effects of farmed escaped cod References Table 1. Allele frequencies for the five markers and two samples of wild cod populations, plus F ST estimates between them. Figure 1. Approximate outer boundaries for Northeast Arctic cod (NEAC) and Norwegian coastal cod (NCC). Sampling sites indicated by filled circles. 20°E 40°E 60°E 65°N 70°N 75°N 80°N 0 200 km Norwegian Coastal cod NCC Northeast Arctic cod NEAC Figure 3. Changes in single loci F IS values in the F1 generation of the native population of coastal cod (NCC) at different levels of introgression by escaped farmed Northeast Arctic cod (NEAC). Values are means of ten simulation runs. 0.01 0.05 0.1 0.25 0.2 0 0.1 -0.1 -0.2 -0.3 -0.4 -0.5 -0.6 F IS F IS Gm1086_03 Gm 335_0159 Gm240_020 Gm1077_07 Pan l Figure 2. Changes in frequencies of the less frequent allele at five markers in the F1 generation of the native population of coastal cod (NCC) at different levels of introgression by escaped farmed Northeast Arctic cod (NEAC). Values are means of ten simulation runs. 0.01 0.05 0.1 0.25 % introgression % introgression 250 200 150 100 50 0 % change in minor allele frequency Gm240_020 Minor allele frequency Gm1086_03 Gm1077_07 Pan l Gm335_015 The simulations demonstrate that in cases where the farmed cod population (e.g. NEAC) is genetically very distinct from the native population (e.g. NCC) allele frequency alterations, even at low rates of introgression, have profound effects on the genetic profile of the native population. This clearly represents a genuine cause of concern. Outstanding questions The introduction of alien escaped cod inevitably raises several questions concerning the genetic impact on native cod in addition to the obvious ecological consequences. • Long-term change in genetic profiles over generations? • Change in migration and spawning patterns? • Change in overall fitness and survival? Layout: Frøydis Strand, UoT Norway Russia Svalbard Ullsfjord Ullsfjord ICES CM2009/Q:18