Modernizing Net Pen Aquaculture: How Submersible Pens are Changing Aquaculture Management

As global food demands increase, more efficient food production strategies have become a focal point of sustainability and food security efforts across the globe. A top priority for many of these efforts is the expansion of aquaculture facilities, which provide a good source of protein at an efficient rate.

While most experts agree that growth of the aquaculture industry is important to ensuring global access to food, fish farming varies from place to place, both in scale and methodology–ranging from indoor Recirculating Aquaculture Systems to more open-water operations, such as net pen aquaculture–which provide their own set of benefits and limitations.

A diver next to Innovasea’s submersible pen. (Credit: Innovasea)

What is Pen Aquaculture

Most simply explained, pen aquaculture, also known as net pen aquaculture, refers to a net pen or floating cage on a lake or open water body that holds farmed fish or fish used to enhance commercial or recreational fishing, according to NOAA Fisheries. 

Pen designs may vary, but a key feature of net pens is that water flows through the site more freely. This approach is in contrast to indoor aquaculture operations, which rely on manual recirculation of the water in order to provide fresh water to the pens consistently.

Benefits of Net Pen Aquaculture

This organic circulation is one of the key benefits of pen aquaculture, though there are many others. 

According to the Food and Agriculture Organization (FAO), net pen facilities optimize space more efficiently than other methods and are also more cost-effective to construct compared to other alternatives.

Pen sizes can be scaled up or down based on the fish being farmed and with respect to the water body being used. Additionally, sites can utilize a large portion of the water column, so even if the pens are smaller in diameter, deeper pens can support larger populations without taking up more space.

Risks of Net Pen Aquaculture

Of course, nothing is without its limitations and risks. In the case of net pen aquaculture operations, high demands for oxygen and water flow are leading concerns, according to the FAO.

They also note that pen operations are at a greater risk of feed losses due to flowing water conditions. Additionally, since there are usually large volumes of fish in each pen, this can accelerate the spread of disease.

There are also possible environmental impacts that need to be considered alongside operations. Daily activities can release nutrients into the surrounding water that can and should be managed through responsible operations. 

In addition to operational risks, there are concerns about how net pen aquaculture impacts ecotourism and the visual impact on coastlines.

Fortunately, a combination of best management practices, environmental monitoring, and quick response times from operators can help minimize some of these risks.

Fish in an Innovasea submersible pen. (Credit: Innovasea)

Responding to Water Quality Declines

Many pen aquaculture operations rely on the use of environmental measurement systems to monitor water quality, but as a result of their location, operators can be limited in how much they can control conditions. 

For example, if dissolved oxygen (DO) declines suddenly, reaction times may be impacted by how often water quality is sampled and how quickly treatment takes to have an effect on water quality.

The use of real-time measurement systems that include real-time alerts is integral to minimizing data delays and ensuring that operators can respond as quickly as possible with treatments or by modifying operations such as delaying feeding.

Quick responses to these events are key to preventing the loss of large volumes of fish or entire pens. Treatments may include the use of an aerator or other oxygenation equipment. Still, many of these responses are dependent on surface water conditions, which can influence the efficacy of treatments.

Submersible Pens

With surface aquaculture pens facing their own set of risks, Innovasea sought to create a solution—something that would be able to get around—or in this case go below—the problem.

The answer is submersible net pens that can be moved up and down the water column depending on water quality and hydrological conditions. Erik Vis, Aquaculture Services Lead for Innovasea, highlights several key benefits to these systems.

In the case of inclement weather, pens can be submerged below the wave zone, reducing structural stress, equipment damage, and the risk of fish escapes resulting from damage to the pens.

In addition to protecting the equipment from damage, being able to move fish out of turbulent water zones can help reduce stress and improve overall health.

Surface conditions, such as harmful algal blooms, jellyfish swarms, temperature extremes, and some parasite concentrations that are often highest near the surface, can also be avoided with the submersible pens.

Submersible pens also make it possible to deploy net pens in more exposed offshore locations that may be unsuitable for surface pens.

Because the pens provide more control, Vis shares that the submerged pens “enable more consistent operations, and steady fish growth regardless of surface conditions.”

The submersible pens also help to remove the visual concerns surrounding pen aquaculture. Zero visual pollution addresses a concern for local residents, helping to make their adoption more palatable.

The Topian submersible pen in action. (Credit: Courtesy of Topian)

How Submersible Aquaculture Pens Work

The Innovasea pens consist of a net enclosure supported by a floating structure that can be submerged or raised with a single switch of an air generator. These pens can operate independently or in a grid depending on the farm’s needs. 

“Buoyancy is controlled using air chambers and flotation systems that allow a single operator to raise or lower the cage in the water column,” explains Vis.

The mobility and flexibility of the systems make submersible pens well-suited for a variety of use cases. 

Though many operators may move the pens up and down the water column more frequently, Vis shares that some users have left systems submerged for prolonged periods in response to long-term water quality concerns. 

For example, Topian, the sustainable food component of the Kingdom of Saudi Arabia’s NEOM project, recently used these submersible pens to protect the fish from high surface temperatures that can last for multiple months.

Environmental measurement instruments can be paired with the pens to help operators identify the ideal position for the pen at that time based on present conditions. A combination of DO, temperature, salinity, currents, waves, and weather sensors may also be used to inform operations such as feeding schedules.

An Innovasea submersible pen from below. (Credit: Innovasea)

Making Pen Aquaculture Management Proactive 

This data helps inform day-to-day operations but also contributes to larger data sets that help improve future management decisions. 

Vis describes this process as transforming “farming from a reactive process into a proactive one. It allows managers to take data-driven actions that improve operations, reduce waste and address concerns.”

The introduction of real-time data collection in particular is essential to keeping farm managers informed of what is happening, without having to be on site.

For example, if low DO or hypoxic conditions are detected by integrated real-time environmental sensors, Vis explains that “operators can move fish vertically within the water column, reduce feeding, or adjust stocking strategies before fish welfare is affected.”

The submersible pens can help operators respond to much more than just DO conditions. When paired with temperature sensors, fish can be moved deeper during heat waves, or to warmer sections of the water column during colder periods to optimize growth and feed conversion.

Some parasites are also depth-specific, so operators can make adjustments as needed to avoid areas where parasites occur most frequently. Similarly, pens can be submerged in response to harmful algal blooms, minimizing impacts to fish health.

“In short, sensor-driven monitoring allows farmers to place fish in the best available environment at any given time, rather than forcing fish to remain in a fixed position,” states Vis.

A diver inspects the bottom of Innovasea’s submersible pen. (Credit: Courtesy of Topian)

How Submersible Pens are Changing the Aquaculture Industry

The power to act quickly and adjust aquaculture operations to meet the needs of the environment is essential to pushing the industry forward and into new areas of the world. 

As Vis explains, “[The submersible pens are] enabling offshore aquaculture in environments where we couldn’t farm before, offering a high-protein food source, and new economic opportunities for the community.”

For example, as coastal farming areas reach capacity, submersible offshore systems provide a pathway to expand operations away from coastlines—increasing global seafood production without relying solely on new nearshore sites.

The pens will also help aquaculture operators respond to changing climate conditions, as farms will be able to better withstand storms, heat waves, and changing ocean conditions.

Overall, these pens are helping transform the aquaculture industry, making operations more robust against traditional challenges, shifting aquaculture from fixed-location farming to dynamic, environmentally responsive farming.

This approach allows fish to be “actively positioned in the safest and most productive part of the water column using real-time environmental data,” explains Vis.

He continues, “This has the potential to improve fish welfare, operational reliability, sustainability, and production capacity simultaneously.”

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