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Existing pilot and commercial facilities demonstrate that offshore aquaculture is technically feasible, and that it can improve growing conditions and farmed animal health under some conditions. Moreover, because offshore aquaculture occurs in ecological contexts that differ significantly from nearshore contexts, different kinds of ecological risks may also arise as the sector grows. Here, we present information on the ecological risks posed by offshore aquaculture and how to mitigate them.
Interest in growing fish, seaweed, and shellfish has grown markedly in recent years in recognition of the growing and potential contribution of aquaculture to marine food production, nutrition, and economic development.
Siting aquaculture operations in waters, where there are fewer claims on marine space and higher water quality, may reduce constraints on marine food production systems. The space available for growing food offshore is considerably larger than is needed to meet global food demand under certain assumptions.
Certain offshore environments also offer natural subsidies, such as higher water quality, flushing, nutrient delivery, and assimilation, with some evidence that the greater depths and currents characteristic of offshore environments also improve growing conditions.
The potential benefits of farming such waters are substantial, but as with all food production systems, its development will not come without some risk to ecosystems and wildlife, particularly if the industry grows sufficiently to contribute significantly to food production, nutrition, and economic development goals.
Here we present a summary of available information on ecological risks posed by offshore aquaculture. Also, knowledge gaps related to characterizing ecological impacts likely to be associated with an expanding U.S. offshore aquaculture sector to help set a national research agenda that could fill these gaps and inform the development of policies capable of facilitating industry growth while minimizing adverse environmental impacts.
Major types of offshore production infrastructure
As interest in offshore aquaculture has grown, several approaches to facility design have emerged. These approaches can be categorized as either open-pen design or closed containment, each with several sub-categories of design within them.
“Open-pen designs are those which use only mesh-style barriers to contain the farmed population, allowing free, three-dimensional exchange between the ‘internal’ farm environment and the ‘external’ ambient environment.”
The most common open-pen designs are surface structures, which suspend mesh fish containment barriers from floating infrastructure, are moored to the seafloor by a series of strategically placed anchors, and have tensioned lines to maintain the shape of the net pen as currents act upon it.
In contrast to open-pen designs, closed containment designs physically separate the ‘internal’ farm environment from the ‘external’ ambient environment. Physical separation allows isolation of the farm population from potentially harmful ambient risks like pathogens, parasites, and algae blooms, as well as the opportunity to remove or treat farm waste products.
However, this eliminates natural subsidies afforded by open pen designs, introducing the need to intake, circulate, and discharge water, as well as maintain its quality to support fish health and growth.
Offshore aquaculture in U.S. waters
There has been increasing interest in growing finfish, shellfish, and seaweed in U.S. offshore waters during the past decade, resulting in greater investment and development of support and research programs. Governance and regulatory systems for offshore aquaculture remain largely under-developed, and very few countries have any regulations that explicitly mention offshore or open-ocean aquaculture.
“Offshore operations can be complicated to regulate under existing legal frameworks because of stakeholder conflict, maritime jurisdictional issues, and understudied environmental impacts.”
U.S. policymakers have pursued a variety of approaches to regulate offshore aquaculture. However, while these efforts are all aimed at increasing U.S. aquaculture production, aquaculture proponents have identified governance, siting issues, and permitting issues as the most significant obstacles to increasing U.S. operations.
In addition, offshore aquaculture requires regulatory certainty and long lease periods to reduce risk for investors and justify large capital expenses associated with constructing and operating a new facility.
The lack of aquaculture-specific federal policy for offshore facilities in the U.S. has driven most offshore aquaculture initiatives to operate in state waters (or in other countries) that offer similar conditions and degrees of exposure to what is expected from sites in federal waters (Table 1).
Ecological risks and knowledge gaps
Many of the practices that have improved nearshore aquaculture outcomes over the past 20 years will likely be employed in offshore aquaculture. However, there may be some attributes of offshore aquaculture that will generate different kinds of risks and thus require different mitigation strategies.
To develop a sound policy that can facilitate the development of the offshore aquaculture industry in U.S. federal waters without compromising the health of ocean ecosystems, it will be necessary to understand the main risks that offshore aquaculture poses to marine ecosystems and wildlife; which risks can be mitigated using current approaches; and which risks will require new or precautionary approaches.
Siting
Selecting appropriate sites for offshore aquaculture presents several challenges, which together create a risk for cumulative impacts. The U.S. offshore marine environment is more crowded than it would appear to be at first glance. As a result, offshore aquaculture facilities have limited possible sites due to a high number of preestablished claims on space and other factors.
Knowledge Gaps:
✓ What is the long-term risk that commercial offshore aquaculture operations would aggregate given the need for favorable growing and operating conditions and existing claims on marine space?
✓ Are the existing regulatory tools appropriate for regulating offshore industry development, or should sector-wide development plans, underpinned by carrying capacity modeling, be used to prevent adverse cumulative impacts?
✓ How can technology best be leveraged to improve siting and monitoring?
✓ What are the best approaches for choosing sites for offshore farms such that production and environmental performance are optimized?
✓ How will climate change affect ecological risk associated with offshore aquaculture given changes in species migration, abundance, and distribution? How can these changes be factored into planning and permitting decisions?
✓ How is the U.S. offshore aquaculture industry going to be monitored effectively in remote locations?
Infrastructure and interactions with marine wildlife
The production and installation of infrastructure (e.g., cages, pens, moorings) capable of containing farmed species in high-energy offshore environments poses a great technical challenge. Offshore aquaculture infrastructure and equipment must withstand or be resilient to strong offshore waves, winds, and currents as well as resist corrosion and fouling.
Plans to use pre-existing infrastructure like decommissioned oil rigs or marine wind farms have been considered globally, including examples such as Belgium’s Wier and Wind project and Germany’s offshore mussel and wind turbine sites.
Loss of or damage to infrastructure during transport, siting, operation, and decommissioning could result in damage to vessels, lethal accidents, and the entanglement and killing of marine animals as the lost gear drifts.
Knowledge Gaps:
✓ How can the risk that aquaculture infrastructure will be lost or damaged during transport and deployment be mitigated?
✓ What are risks associated with decommissioning an offshore aquaculture facility?
✓ While fishing pressure could be addressed with existing management frameworks, what are the most effective strategies for mitigating other risks associated with fish and wildlife interactions with offshore aquaculture infrastructure, like disease transmission or entanglement?
Stocking
With few exceptions (e.g. tuna ranching operations), stock for on-growing at offshore finfish farms is expected to come from hatchery production.
For well-established farmed species, broodstock are obtained from hatcheries which are typically sited on land. For more novel species, broodstock may be wild caught, and risks include over- exploitation of the wild population and by-catch during collection, though the relatively few individuals necessary for broodstock cohorts limits this risk.
The environmental impacts of land-based brooding and rearing systems include habitat modification for facility construction, operational energy and water consumption, and metabolic waste disposal. In U.S. hatcheries, most of the energy consumed is for water circulation and feed distribution, and most of the energy is sourced as electricity or natural gas.
Knowledge Gaps:
✓ What data are necessary to collect to determine optimal stocking densities for a specific species in a given locale? How should the optimum be defined?
✓ What are the most efficient strategies to produce sufficient stock for each of the species being considered for offshore production and how can the constraints on their production be overcome?
✓ How can the carbon footprint of hatcheries and pre-stocking rearing operations for offshore farms be further reduced?
Feed
Feed is a critical driver for the economic and environmental footprint of aquaculture; for example, feed generally represents 50–80% of production costs of fed aquaculture and is typically the most significant contributor to fed aquaculture’s greenhouse gas emissions.
Additional environmental concerns with feed include overall efficiency of converting feed to aquatic animal growth, the sustainability of feed ingredient resources, and the effects of feed lost to the environment.
Feed production and use for aquaculture occurs within a broader food systems context, necessitating the consideration of a wide range of environmental impacts, including to terrestrial and freshwater habitats.
Knowledge Gaps:
✓ What are the most feasible ways to continue to incentivize the efficient use of fishmeal and fish oil content in aquaculture feeds?
✓ How can robust and consistent understanding of the ecological and social implications of feed use and manufacturing be achieved?
✓ What are the key performance indicators and targets for fed aqua- culture (e.g., FCR, FFDR, GHG emissions) to be considered for sufficiently responsible offshore production in the U.S.?
✓ How do the respective environmental consequences of current and future feed ingredients compare and what are their limitations?
✓ How can technological, policy, and market developments accelerate the process of improving feed conversion ratios and feed formulations?
✓ What are the next steps in the industry for using technology to reduce feed loss, and how can feeding efficiency be further improved?
Disease
While diseases and parasites are initially transmitted from wild to farmed fish, their amplification in aquaculture conditions is of concern. For offshore farms, the increased physical distance of facilities from the shore reduces interaction with coastal flora and fauna and minimizes the risk of disease and parasite infections.
Environmental modeling and spatial planning can be used to assess hydrodynamic connectivity and minimize disease transmission. Concerns about disease outbreak due to cumulative impacts of multiple farms in the same area can be mitigated with the management of spatial distribution of farms.
Knowledge Gaps:
✓ What are the population level impacts of offshore escapes on marine ecosystems?
✓ How can existing monitoring systems, used to detect outbreaks of disease, parasites, and fish escapes, be further improved and coupled with protocols to minimize potential risks to wild species and ecosystems?
✓ What siting criteria would minimize the risk of disease and pathogen outbreaks within farms, as well as minimize spread to local wildlife?
✓ Will certain types of offshore aquaculture infrastructure pose fewer risks of escapes than others?
✓ Is the use of cleaner fish likely in offshore aquaculture, and if so, would this practice pose ecological risks due to escapes and can it address concerns around cleaner fish welfare and overharvesting?
✓ How can the prevalence and distribution of pathogens in wild populations be better characterized to better understand disease trans- mission to farmed animals and vice versa?
Conclusions
Although offshore aquaculture is a nascent industry globally, many pilots and several commercial operations have demonstrated that it is technically and perhaps economically feasible, and many lessons can be learned from them.
Many of the ecological risks associated with offshore aquaculture can probably be mitigated using well-established methods. The risk of cumulative impacts arising from the need to satisfy several siting criteria simultaneously can be managed with planning processes and cumulative risk modeling and analysis.
Stocking can be optimized through continued research on how to take advantage of higher currents and other conditions that can improve growth conditions and reduce the need for high stocking densities.
Feed impacts can be mitigated by advances in the development of low-carbon and cost-effective alternatives to fishmeal/fish oil and continued improvement in food conversion ratios, as well as through the continued development of precision feed delivery systems that minimize feed loss.
Offshore aquaculture in the United States has strong potential for positive impacts, such as benefiting local seafood production and economic development. U.S. aquaculture facilities operating within a strong and well enforced regulatory system could potentially produce seafood with relatively fewer environmental impacts compared to seafood grown and harvested in contexts with weaker regulation, or in areas that are farther from major markets.
More research will be required to fill remaining knowledge gaps related to the characterization and mitigation of ecological risks associated with offshore aquaculture, both to develop best practices and performance standards, and to develop policies that ensure the adoption of these practices and standards.
This is a summarized version developed by the editorial Team of Aquaculture Magazine based on the review article titled “TOWARD AN ENVIRONMENTALLY RESPONSIBLE OFFSHORE AQUACULTURE INDUSTRY IN THE UNITED STATES: ECOLOGICAL RISKS, REMEDIES, AND KNOWLEDGE GAPS” developed by: ROD FUJITA – Environmental Defense Fund; POPPY BRITTINGHAM – Stanford University; B, LING CAO – Shanghai Jiao Tong University; HALLEY FROEHLICH University of California; MATT THOMPSON – New England Aquarium; TAYLOR VOORHEES – Monterey Bay Aquarium and Cargill, Inc.
The original article, including tables and figures, was published on OCTOBER, 2022, through MARINE POLICY.
The full version can be accessed online through this link: https://doi.org/10.1016/j.marpol.2022.105351
