World Aquaculture - December 2023

26 DECEMBER 2023 • WORLD AQUACULTURE • WWW.WAS.ORG Norway, genetic introgression is generally considered the second largest environmental problem resulting from salmon farming after the parasitic salmon louse. Why are wild x farmed fish unsuited for a life in the wild? Farmed fish have been domesticated through 50 years of selective breeding. This has the benefit of reducing production times by removing unwanted traits and selecting fast growing fish which grow well in the farm environment. Recently, the egg supplier AquaGen AS estimated that selective breeding of their sires alone had increased harvest weight by 40 percent while simultaneously reducing the amount of time fish need to spend in seawater to reach 4 kg (market size is 4-5 kg) from 17 to 9 months between 2003 and 2021 (Næve et al. 2022). However, the traits that are beneficial for living on the farm are not beneficial for a life in the wild (Solberg et al. 2020). For example, fast growth is demanding on the body and encourages more risky behavior to find food which makes farmed salmon easier for predators to catch. In Norway, over 1 million farmed salmon have escaped in the last decade with 6.8 million since records began in 1998 (Figure 1C). This normally happens when holes develop in the nets. These escapees only make up a small fraction of the total salmon being farmed in Norway every year, which stood at 426 million individuals in 2021. But in the most recent surveys, Norway is home to only 480 thousand wild salmon! That’s 0.1 percent of the number of farmed salmon today, and down from around 1.1 million wild salmon in the Norwegian aquaculture and the problem of fugitive salmon Norway is the world’s second largest producer of cultured marine and coastal finfish and 93 percent of its production is Atlantic salmon (Salmo salar) (FAO 2023). Its salmon industry has grown enormously since the early 1970’s when the first farms began. Now producing 1.4 million metric tons annually, with an export value of 106 billion NOK’s (€9.9 billion/$10.7 billion) in 2022 (Norwegian Seafood Council 2023), Norway is and always has been the largest producer of farmed salmon globally (Figure 1A). This success has been founded on Norway’s local environment, that is home to some of the world’s largest wild salmon populations. And at over 100,000 km in length, its coastline provides many potential farming locations with 990 sea sites in operation in 2021 (Directorate of Fisheries 2023). Despite the early success, the industry’s growth has been relatively stagnant for the last decade due to environmental challenges (Figure 1B). One of the major worries is the impact farm escapees are having on wild populations through a phenomenon termed “genetic introgression.” This refers to interbreeding between two strains of Atlantic salmon: wild and farmed. This produces crossbred fish maladapted for a life in the wild, and enhances the pressure on wild salmon stocks which are already struggling under the multiple burdens of habitat loss, overfishing, disease, and climate change (The Scientific Council for Salmon Management 2021). In Norway’s Experiment with Triploid Atlantic Salmon: From Small-scale Successes to the Suspension of Commercial Trials Thomas W. K. Fraser, Per Gunnar Fjelldal and Tom J. Hansen FIGURE 1. Atlantic salmon production. (A) Global Atlantic salmon production. Data from FAO (accessed 2023). (B) Atlantic salmon production in Norway over time. Data from FAO (accessed 2023). (C) The number of reported Atlantic salmon escapees in Norway. Data from the Directorate of Fisheries (accessed 2023).