For a long time, global mariculture has primarily operated in coastal waters. However, intensive farming and unsustainable practices have led to growing conflicts with other coastal activities like shipping, tourism, and conservation. This crowded space often results in environmental degradation, fish escapes, and disease spread in near-shore areas.
To address these challenges, the industry is turning to more expansive and environmentally friendly locations: the deep sea. Deep-sea aquaculture offers vast ocean space, reducing conflicts with other marine sectors. It also provides superior water quality and sustainable, natural water exchange, paving the way for more sustainable seafood production.
The Evolution of Key Technologies
Utilizing deep-sea conditions for fish farming has emerged as the optimal choice for ensuring a stable supply of high-quality fish. Pioneered by fishing nations like Norway, the US, and Sweden, the main technological directions are large-scale nets and aquaculture platforms.
Supported by modern technology, these nations have rapidly advanced the automation of large farming nets. The development and application of information technology have significantly boosted efficiency and improved management control.
Projects like Europe’s “Offshore Large-Scale Net Pen Platform” integrate various technologies—including large nets, offshore wind power, remote monitoring, high-quality fry breeding, eco-friendly feed, automated feeding, and health management—forming a comprehensive deep-sea aquaculture engineering system.
Another key research direction is the use of Aquaculture Vessels. Since the 1980s and 90s, advanced fishing nations have been developing various platforms, including floating structures, ship-based farming compartments, and semi-submersible net-pen vessels. These innovations have yielded significant results and built a solid technological foundation for industrial-scale development.
Classification and Designs of Aquaculture Systems
Based on current deep-sea farming conditions, the equipment can be divided into two main categories: Open Net Pen Systems and Closed Containment Systems.
1. Open Net Pen Systems
Open net pens are widely used for marine fish farming. In Norway, for instance, systems designed with a 50-year lifespan are deployed in waters with significant wave heights of 2-3 meters, classified as “partially exposed.”
Floating Flexible Pens: Often made with HDPE (High-Density Polyethylene) pipes for buoyancy, these pens are assembled into floating frames, combined with nets and mooring systems. Their high elasticity allows them to withstand waves, and they typically last over 10 years.
Floating Rigid Pens: These feature sturdy, often steel, frames, offering advantages in strength, stability, and buoyancy. They provide a stable platform for operations and can integrate automated feeding and harvesting systems. Support facilities like feed storage and cranes can be installed. While they can be built in traditional shipyards, their drawbacks include the need for heavy structures, expensive installation, vulnerability in extreme weather, and costly mooring systems.
Semi-Submersible Flexible Pens: Their key feature is the ability to submerge to a certain depth during storms or typhoons, minimizing damage. However, the need for submergence capability increases design complexity, difficulty, and cost.
Semi-Submersible Rigid Pens: These use rigid frame units, often steel, to prevent movement and volume changes from waves and currents. Equipped with adjustable ballast tanks, they can be raised or lowered to avoid severe weather. This design can also avoid wave resonance. Submerging during typhoons enhances safety for the structure and the fish, but construction costs are high.
Fully Submersible Pens: These systems normally operate at a safe depth below the dangerous surface layer but can be temporarily raised for maintenance or harvesting. Several designs, like Sadco, AquaPod, and NSENGI, have been developed, with some already in exploratory trials or commercial use.
2. Closed Containment Systems
Introduced in the 1990s to better control water quality and the production process, these systems were initially land-based with water recirculation systems. To protect farmed fish from sea lice and parasites, floating closed systems were developed for deep-sea use.
These systems continuously replenish water, helping maintain proper temperature and oxygen levels while removing waste. Their main advantage is controlled water exchange, allowing for continuous disinfection to keep out pathogens. External events like algal blooms no longer impact the fish, and organic waste is removed via biofilters before water is discharged. Threats from predators are also eliminated.
Compared to open nets, these systems offer greater control, allowing for the optimization of physical parameters to maximize productivity. However, deploying them offshore requires a power supply, which can be costly if transmitted from land. They also involve high construction and equipment costs, require more intensive management for monitoring, and must mitigate the effects of internal water sloshing on the structure and the fish.
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