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Evolving Net Pens for Fish Culture - Reinventing the Wheel?

More than 20 years ago there a Pacific NW based company, Mariculture Systems, developed and patented a methodology for growing salmon outdoors in an enclosed environment. They named it SARGO, a floating rigid wall tank. They were several decades ahead of their time. They noted that there are several potential challenging environmental issues with net pens.

These are illustrated below. Several units were tested in the Pacific NW and elsewhere. Testing successfully demonstrated the concept in both Coho and Chinook salmon as well as Arctic char. Despite the promise of the technology, they simply were too far ahead of the potential demand. The company shut down and the technology was abandoned.

Today we are seeing a number of companies looking at similar approaches. These systems have the potential for eliminating the objections of those that are focused on what they might consider to be the negative aspects of net pen aquaculture. They also can improve productivity. The challenges are to ensure the safety and integrity of the crop and ultimately to lower the cost of production.

The basic element of the SARGO fish rearing system was a floating, rigid‐wall reservoir with a continuous, external supply of water pumped from depth. Six fish‐rearing reservoirs assembled around a service platform comprised a pod. Each service platform contains the pumps, controls, feeding equipment, oxygen supply, waste handling system and other support equipment for its pod. No system ever made it to the point of commercial operation, but there were several that were evaluated under field conditions.

Major testing had been conducted on Coho and Chinook salmon (saltwater), and Arctic char (freshwater), as well as Yellowfin tuna in Panama and Walleyed pike in freshwater lakes in Michigan. Mariculture Systems worked with Yellow Island Aquaculture on Quadra Island to install a system to raise Chinook salmon, to be operational by the spring of 2008. The system was expected to be able to produce market size 3.6‐3.9 Kg (8 – 8.5 lbs.) in approximately 15 months at a cost that would have been competitive with net‐pen production. They previously harvested 2 cycles of Atlantic salmon in Puget Sound (2001 – 2002). These grew to market size 3.6‐3.9 Kg (8 – 8.5 lbs.) in 10.5 months, outpacing average net‐pen production for Atlantic salmon.

Their 2nd generation tanks were 20 m in diameter and 11.5 m deep with a total of 2500 m3 usable space. There was a 5ft high level barrier from the open water to top of tank to minimize liquid transfer. The fabric was a high-density polyethylene with steel reinforcement and fiberglass bottom, which had the advantage of very low growth of organisms on the sides so there is less drag from fouling compared to nets. It was designed to withstand winds of up to 160 km/h.

Water was pumped in locally (either ocean or lake water) and was filtered to remove particulates or any organisms before going into the tank. Intake pipes reached depths as great as 280m (>900 ft) with the ability to select the source of intake to control temperature and salinity as well as water quality. The waste treatment system was a Type III marine sanitation device (designed for the shipping industry). They also explored anaerobic digesters to create methane and wave‐energy generators for low-cost energy generation. Ultimately, the pods would be entirely self-sufficient for ‘far from shore’ open ocean deployment. In tests they saw excellent feed conversion ratios of 1.15.

This system offered the ability to eliminate waste streams, closure of the system to avoid the deleterious impacts of algal blooms and a means to ensure that potential pathogens were not dumped into aquatic ecosystems. Field testing proved the concept. Unfortunately, the demand was not there as at the time concerns about potential environmental impacts of salmon farming were not issues. They should have been as humanity is learning the hard way that we can have broad and seriously negative impacts on the overall quality of life by thinking that the atmosphere, the oceans, and the land are incapable of being altered negatively by human activity. This has been increasingly obvious for many years but widely ignored for the sake of profit.

Much of the current issues concerning net pens are not based on science. NGOs and environmentally concerned organizations focused on what they perceived to be the negative aspects of cage culture. Among these were the waste streams from net pens, the potential of fish escaping and the presence of pathogens that might be transferred to local stocks. Raw and partially treated human sewage is the real problem as the consistent increase in localized algal blooms in estuaries around the planet is demonstrating. Fish can and do escape from net pens sometimes in large numbers. There is no evidence though that this results in local damage to wild stocks. The damage is from human development and apathy. As for disease transmission. The diseases that impact farmed animals typically are present in wild stocks, albeit at low levels. Holding large numbers of fish in traditionally designed net pen enclosures can allow pathogens to move between animals in a manner that is much different than what typically occurs in the wild. Many of the pathogens affecting farmed fish are opportunistic and would not impact healthy non-stressed animals.

The use of the SARGO system prevented all of these issues. Waste streams are treated and not added to the environment, killing any potential pathogens. Fish cannot escape because of fouling of net pens or damage from weather or human activities. If they learn from what has been done before then we can look forward to a significant paradigm shift that does not entail growing fish on land in RAS systems with their technological hurdles and high costs.

The only complaints might be from landowners who don’t wish to have their vistas impacted by the reality that farmed fish are needed to supply a high-quality food source to a world that is not in balance. Demand for wild fish and the impact of global climate change is stressing many wild populations and it is no secret that human activity has destroyed many native habitats and overfishing is still all too common. While no system is perfect it remains to be seen how effective the coming generation of these enclosed systems handles these issues. Based on the technology that SARGO pioneered decades ago there is reason to believe that we can produce high quality farmed aquatic animals without the potential for what some perceive of negative impacts.

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