22 MARCH 2024 • WORLD AQUACULTURE • WWW.WAS.ORG FIGURE 1. The development in Danish blue mussel cultivation. PHOTO 1. Mussel longlines. Courtesy Danish Aquaculture Producers Organization (DAPO). Danish LTA production is almost exclusively blue mussels. The development in volume and value is shown in Figure 1. From 2017 to 2022 the share of production volume has increased from 4% to 19% while the share in value has increased from 1% to 3%. An additional 5 tons of seaweed (Saccharina latissimi) was produced in 2022. Mussel farming uses longline technology and tubenet systems (Photo 1). Mussels are generally sold in big bags to wholesalers in the Netherlands where they are re-packed and distributed to the market. More than 95% of the production is exported and some 90% of the production is certified organic. The Danish aquaculture strategy acknowledges the growth potential and the ‘additional’ ecosystem services provided by mussel farming, but there is also concern related to visual impacts, competition for space, and local environmental impacts, in particular related to multiple mussel farms. Such concerns, combined with an increasing number of license applications led to a temporary moratorium on new licenses for mussel farming lasting from 2021 until today. Mussel farming for mitigation aims to optimize total biomass production at the lowest cost. Such farming might be a cost-effective marine measure, but it has not yet been decided to adopt mussel farming as a mitigation tool since it is dependent on public incentives13. The new Danish Maritime Spatial Plan covers the Danish marine area and includes zones for farming of shellfish in the water column. Public authorities may only grant permits within defined development zones, and this might limit the sub-sectors’ access to space. Despite the overall political goodwill and the public funding of numerous development projects, the Danish LTA sub-sector still almost exclusively produces blue mussels. The short-term outlook for the sub-sector thus depends mainly on policy decisions in relation to lifting the moratorium, the number and location of useful zones for shellfish farming in the Maritime Spatial Plan and the potential use of mussel farming as a mitigation tool. Freshwater Farming Pond farming in Denmark dates back to the 19th century when the first farms were established. These were flow-through earthen ponds within the numerous rivers/streams in the Jutland peninsula, and mainly farming rainbow trout (Photo 2). The number of flow-through farms have declined from some 500 in 1989 to 66 in 2022. They cover a wide range of activities including breeding/ egg production, production of fry and fingerlings, organic farming, and production of different market size fish and species. In recent years this sub-sector has developed dramatically, and a significant shift from traditional, extensive farming towards more intensive farming in (semi-) recirculated systems has occurred. The introduction of the so-called ‘Model Trout Farms’14 in 2004 initiated a change from flow-through to recirculated freshwater farms. The Model Trout Farm concept was based on applying pre-designed recirculation technology on existing flow-through farms and converting the earthen ponds to constructed wetlands (Photo 3). The concept also introduced emission-based regulation. The emission-based regulation limits both the total emissions to the water environment as well as the specific emissions (discharge per kg farmed fish) to ensure compliance with the Best Available Technology (BAT) concept enforced in the Danish Environmental Protection Act. The combination of pre-designed configurations and emission-based regulation linked investments in technology to production output (Photo 4). While flow-through farms are still regulated by the amount of feed they can use, Model Trout Farms / recirculating aquaculture farms are regulated by their discharge of nutrients (N & P) and organic matter. This change in regulation accelerated structural development in the sub-sector, with the establishment of larger PHOTO 2. Traditional pond-based trout farm. Courtesy DAPO.
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