Erfðablöndun villts íslensks lax (Salmo salar) og eldislax af norskum uppruna / Hybridization between wild Icelandic salmon (Salmo salar) and farmed salmon of Norwegian origin HV 2023-25

Ágrip

Erfðablöndun við eldislax getur breytt erfðasamsetningu villtra stofna, leitt af sér breytingum í lífsögulegum þáttum og jafnvel valdið hnignun stofna. Á Íslandi er sjókvíaeldi á laxi af norskum uppruna vaxandi atvinnugrein. Framleiðsla á eldislaxi hefur farið úr því að vera nánast engin árið 2010 upp í 43.000 tonn árið 2022. Samkvæmt núgildandi ráðgjöf Hafrannsóknastofnunar (áhættumat erfðablöndunar) er talið að hægt sé að ala 106.500 tonn af frjóum laxi án þess að það valdi neikvæðum áhrifum á nytjastofna villtra laxa. Í erfðarannsókn frá 2017, þar sem notast var við 15 örtungl (e. microsatellites), fundust merki um erfðablöndun í ám í nálægð við sjókvíaeldi á Vestfjörðum. Í þessari rannsókn voru laxasýni tekin í ám hringinn í kringum landið og sýnafjöldi var tæplega tíu sinnum meiri. Alls voru 6.348 laxaseiði úr 89 ám rannsökuð og áhersla lögð á svæði í nálægð við sjókvíaeldi. Flest sýni tilheyrðu hrygningarárgöngum 2014-2018 þegar framleiðsla á eldislaxi var um 6.900 tonn að meðaltali. Sýni voru erfðagreind með 60.250 samsætum (SNP-erfðamörkum) og erfðaupplýsingar 250 eldislaxa nýttar til samanburðar. Stuðull erfðamunar (FST) milli íslenskra laxa og eldislaxa var 0,14 að meðaltali (miðað við 34.700 SNP) og 0,62 fyrir þau erfðamörk sem sýndu mestan aðskilnað milli hópanna tveggja (196 SNP). Erfðablöndun var greind með fjölþáttagreiningu (PCA) og í líkönum forritanna ADMIXTURE, STRUCTURE og NewHybrids. Alls greindust 133 fyrstu kynslóðar blendingar (afkvæmi eldislaxa og villtra laxa) í 17 ám (2,1% sýna, innan 18% áa). Eldri blöndun (önnur kynslóð eða eldri) greindist í 141 seiðum í 26 ám (2,2% sýna, innan 29% áa). Fyrstu kynslóðar blendingar voru algengari á Vestfjörðum en Austfjörðum sem er í samræmi við að eldið á Austfjörðum hófst síðar og hefur verið umfangsminna. Erfðablöndun greindist yfirleitt í minna en 50 km fjarlægð frá eldissvæðum en nokkrir blendingar fundust í allt að 250 km fjarlægð. Aftur á móti var eldri erfðablöndun tíðari á Austfjörðum en Vestfjörðum og tengist líklegast eldinu sem þar var starfrækt í byrjun þessarar aldar. Eldri erfðablöndun var mest áberandi í Breiðdalsá og greindist í 32% (72 af 228) seiðanna. Þörf er á frekari rannsóknum á kynslóðaskiptingu blendinga, umfangi og orsökum dreifingar eldri blöndunar. Rannsóknin greindi sem fyrr segir áhrif frá upphafsárum núverandi eldis, meðan framleiðslumagn var lítið, og eldri tilrauna í sjókvíaeldi. Niðurstöðurnar í þessari skýrslu sýna að erfðablöndun hefur orðið við hlutfallslega lítið eldismagn.

Abstract

Hybridization of farmed salmon with wild populations can alter local genetic composition, lead to changes in life-history traits and possibly even population declines. In Iceland, production of a Norwegian origin of salmon in sea-cages is a growing industry. Production of farmed salmon has gone from almost nothing in 2010 to 43,000 tons in 2022. According to the current advice of the Marine and Freshwater Research Institute (risk assessment of genetic mixing) 106,500 tons of fertile salmon can be farmed without causing a negative impact on harvestable wild salmon populations. In a genetic study from 2017, analysis of 15 microsatellites revealed signatures of hybridization in the vicinity of salmon farms in the Westfjords. In this study, sampling was conducted around the country and the number of samples was almost ten times higher. A total of 6,348 salmon juveniles from 89 rivers were studied with emphasis on areas close to salmon farms. Most samples belonged to the spawning cohorts of 2014-2018, when the production of farmed salmon was 6,900 tons on average. Samples were analyzed with 60,250 single-nucleotide polymorphism (SNP) markers, with genetic information of 250 farmed salmon used as a baseline. A summary of genetic difference (FST) between Icelandic salmon and farmed salmon was 0.14 on average (34,700 SNPs) and 0.62 for the SNP‘s showing the greatest differentiation between the two groups (196 SNPs). Hybridization was analyzed by principal component analysis (PCA) and with model approaches implemented in the softwares ADMIXTURE, STRUCTURE and NewHybrids. A total of 133 first-generation hybrids (offspring of farmed and wild salmon) were detected in 17 rivers (2.1% of samples, in 18% of sampled rivers). Older hybridization (second generation or older) was detected in 141 juveniles in 26 rivers (2.2% samples, 29% of rivers). First-generation hybrids were more common in the Westfjords than in the Eastfjords, which follows the fact that the current farming in the Eastfjords started later and is less extensive than in the West. First-generation hybrids were usually detected less than 50 km from farming areas, but few were found in rivers up to 250 km away. Older hybridization events, on the other hand, were more frequently detected in the Eastfjords than in the Westfjords and is most likely related to the farming that operated there at the beginning of this century. Older hybridization events were most noticeable in the River Breiðdalsá and were determined in 32% (72 out of 228) of juveniles. Further examination of the generational range of hybridization, as well as the extent and causes of the spread of older hybridization events is needed. As mentioned above, this study focuses on the initial years of the ongoing salmon farming operations, while the production volume was low, and the effects of earlier experiments in salmon sea-cage farming. The results show that hybridization has occured at relatively low production levels.