The ectoparasitic copepods of the family Caligidae are well known for their impact on modern sea cage aquaculture of salmonids. A rather overlooked approach to sea lice management is to use the natural filter-feeding ability of bivalves. In this study, on the example of mussels in the genus Mytilus, we explore the feasibility and expected size of a bivalve biofilter against planktonic stages of sea lice. We measured the filtration of planktonic Lepeophtheirus salmonis larvae by blue mussels (M. edulis) in laboratory experiments and combined the measured filtration rates with filtration rates calculated from raw data from comparable studies. The combined results suggest that 50 mm mussels filter sea lice nauplii with a mean rate of 1.66 L & sdot;h-1 and copepodids with a mean rate of 0.46 L & sdot;h-1. The observed differences in filtration amongst larval stages indicate that a mussel biofilter will be more effective at preventing the release of sea lice larvae from a salmonid farm than at preventing the entry of the infective stage. Upscaling to a typical salmonid aquaculture setting, we estimate that several million blue mussels would be needed to filter 10% of all passing copepodids and 30% of all passing nauplii, corresponding to more than 10000 m of mussel rope per open-net cage. In smaller settings, around 1 million mussels corresponding to more than 1 000 m of mussel rope would be needed. Our estimates may be used in future modelling and planning of combined salmonid-mussel farms.

This study presents a comprehensive computational framework for the structural analysis of an offshore aquaculture structure subjected to stochastic ocean loading. As an example, the methodology is applied to an Integrated Multi-Trophic Aquaculture (IMTA) platform AquaFort considered for deployment in the Gulf of America. A reduced-order finite-element model of the IMTA structure was developed in a dynamic Morison-equation-based software Hydro-FE integrated with Hexagon Marc. The model was compared with a 3D detailed SolidWorks model, showing displacement differences below 6 %, but relatively large von Mises stress discrepancies up to 37% which was improved to 7-16 % by reconstructing cross-sectionally resolved stress fields using beam-element sectional forces and moments. Environmental forcing used random-phase realizations of a 1-year return-period wave spectrum. Wave phase variability produced up to 46% variation in peak mooring tension within 95% confidence interval. A Monte Carlo approach was applied to select storms with prescribed exceedance probability. The numerical model incorporated Reynolds number (Re)-dependent drag to consider seasonal viscosity effects and net-induced velocity reduction. By combining Hydro-FE dynamics, stochastic loading, season-sensitive Re-dependent fluid drag coefficients, and stress reconstruction, the methodology provides a numerically efficient framework for evaluating structural reliability of offshore aquaculture systems under realistic environmental variability.

To expand shellfish aquaculture offshore without risking whale and sea turtle entanglement, we investigated growing three different shellfish species in bottom cages. Atlantic sea scallops, eastern oysters and blue mussels were cultured in cages at three different locations, including a deep fully exposed site, a shallow, fully exposed site, and a shallow, partially exposed site. Each two-cage trawl housed all three species and was equiped with a different type of “ropeless” gear including SMELTS lobster Lift, EdgeTech 5112 Ropeless Fishing and Subseasonic TR4RT timer release system. We evaluated growth and survival of each species and performance of each ropeless release system at these three locations over a one-year growout period. Scallops showed excellent (>90%) survival and growth (0.09-0.11 mmd-1) at both the deep fully exposed site and shallow, partially exposed site when compared to standard culture methods. Oysters and mussels had slow growth at all sites compared to standard culture methods. Gear held at deep sites also contained virtually no biofouling after one year without cleaning. We then performed an economic analysis on scallops using different gear types and trawl lengths to determine circumstances where bottom culture would be profitable.

To meet growing seafood demands, the US aquaculture industry will need to consider farming the open ocean in a responsible manner. However, offshore environments can be energetic (seas > 8 m) making it difficult to maintain surface cage systems. To minimize potential storm damage, submerged culture technologies can be employed to safeguard the infrastructure and product. Steelhead trout (Oncorhynchus mykiss) have potential as an offshore species, though they have open air bladders (physostomous), and need access to air to inflate their swim bladders. To address this concern, three experiments were developed to explore the ability of O. mykiss to cope with extended periods of submergence. The studies used small (~300 g) and large (~1000 g) trout, in cages that ranged from 3.7 to 68 m3, that were submerged for periods of one to four weeks. Data storage tags (DST), sonar and video were used to quantify their ability to manage with submergence. Results indicated differences in growth, condition, and mortality among the treatments. The study suggests O. mykiss can be submerged for days to weeks with no negative effects, but that submergence times >3 weeks can be detrimental. It is therefore recommended that when culturing O. mykiss in areas exposed to severe storms or hazardous environmental conditions (e.g. harmful algal blooms or icing), submersible cages should be utilized to avoid these events up to 3 weeks.

Sugar kelp (Saccharina latissima), a brown macroalga, is a vital crop in the burgeoning seaweed aquaculture industry. As seaweed farms expand, the traditional practice of collecting wild sporophytes will be unsustainable. Developing new kelp cultivars that suit multiple farm conditions is necessary. To address this challenge, our breeding project selected six sugar kelp crosses to be grown in New Castle, New Hampshire; Duxbury, Massachusetts; and Moriches, New York, in the 2022-2023 growing season. We measured four plot level traits (wet weight, dry weight, sporophyte density, and percent dry weight), five single blade level traits (blade length, blade maximum width, blade thickness, stipe length, and stipe diameter), and three tissue composition traits (ash content, carbon content, and nitrogen content). All plot level traits except for the percent dry weight were affected by both crosses/genotypes (G) and farm site/environments (E). All blade level traits were significantly affected by crosses. Farm effects were only detected on blade maximum width and stipe diameter. For the tissue composition traits, ash content was not affected by either cross or farm site. Carbon content was only significantly affected by the farm site, while the nitrogen content was affected by farm site, cross and their interaction effects. These findings suggest that multi-farm testing for sugar kelp breeding programs is important for determining the best crosses for various growers. Understanding G by E effects can advance sugar kelp breeding for targeted traits and farms that will facilitate the adoption of cultivars toward sustainable economic growth on diverse kelp farms.

This study advances techniques to measure the distribution and behavior of steelhead trout in a sea cage in fluctuating tidal currents. An ultrasonic telemetry system (Hydroacoustic Technology Inc., model 291) was deployed around a 63 m3 sea cage stocked with 200 steelhead trout (Oncorhynchus mykiss). Fish and net twine movements were monitored using 20 ultrasonic tags. Eight of these were implanted into the abdominal cavities of sentinel trout, with the remaining attached around the net bottom and midsection. The signals were detected by four omni-directional hydrophones that were connected to a receiver on a nearby pier. Signals detected at 2 s intervals were used to plot three-dimensional locations of thefish. We found that current flow inside the net was significantly reduced (32-53 %) compared to outside, and that swimming behavior was influenced by tidal currents. As current speed increased, the fish swam into the current to maintain their position, and the volume occupied by the eight-sentinel fish decreased. In contrast, during slack tides, the fish swam in a circular pattern, and the sentinel fish used more of the cage volume. This study demonstrates the use of acoustic telemetry to study fish behavior in a cage experiencing tidal currents. This technology can be applied to commercial scale cages to improve fish welfare and cage design.

In response to stakeholder conflicts, coastal pollution, and spatial constraints limiting sustainable nearshore aquaculture, offshore farms have emerged as a potential solution. However, offshore farms are exposed to energetic wave-current conditions and require a rigorous engineering approach to reduce failure risk. This paper presents a methodology to evaluate the risk of structural failure of offshore mussel farms in response to extreme wave and current conditions using a representative mussel farm design in New England offshore waters. This includes a three-step methodology: (1) Computational fluid dynamics-derived drag coefficients: 2D OpenFOAM simulations determine normal and tangential drag coefficients for mussel droppers; (2) Hydro-elastic finite-element modeling: a time-domain finite-element model driven by Airy-wave kinematics and Morison loads to predict mooring, mainline, strap, and dropper responses under 10-, 25-, and 50-year return-period wave and current scenarios; and (3) Statistical risk assessment: simulation outputs are interpolated to create a continuous response field across the full range of wave heights and current speeds, which is then integrated with a joint probability density function of significant wave height and current speed-alongside component ultimate and residual strength at three growth phases-to estimate failure probabilities over specified design lives and recommend optimized safety factors. Results indicate that combining accurate drag coefficients with a continuous response surface and joint-PDF risk analysis enables systematic estimation of component failure probabilities and informs appropriate safety-factor selection. Thus, the proposed integrated methodology can be used to quantify structural failure risk and support informed design decisions for reliable offshore aquaculture structures.

Semi-rigid fiberglass/vinylester composite lines are being investigated as a substitution of traditional synthetic lines in offshore aquaculture mooring systems in an effort to prevent or mitigate large marine mammal entanglement. This paper briefly outlines a comprehensive set of field studies, laboratory tests, and numerical approaches utilized in the project. One of the laboratory studies investigating full-scale interaction of a composite line with North Atlantic Right Whale appendages is presented in detail. It is shown that in the case of such interaction the whale will likely break the line and avoid entanglement.

With the expansion of macroalgae aquaculture in oceanic waters, especially of order Laminariales, a need exists to have optimized cultivation systems suitable for exposed conditions. To enable the design of such systems with a quantifiable level of confidence, in this paper, we developed a high-fidelity hydrodynamic modeling technique for kelp farms by introducing equivalent kelp elements for kelp aggregates with Reynolds number-based drag coefficients. After validating the model with towing tests for model kelp aggregates, it was then compared with comprehensive field datasets for a single line cultivation system with two mooring connections, in Saco Bay, Maine. The model yielded a larger tension than the measured tension by 23.3% on the west mooring line but a smaller tension by 23.2% on the east mooring line. The discrepancies may be caused by the uncertainties in the model configuration and input due to difficulties quantifying exact longline orientation, anchor-anchor distance, current reduction along the kelp longline, kelp mass density, and rope axial stiffness. Sensitivity analysis indicates that addressing these uncertainties may improve the model technique. Even though, the developed model is still reliable with a safety factor in the application for the design, installation and management of kelp aquaculture farms.

Aquaculture in exposed and/or distant ocean sites is an emerging industry and field of study that addresses the need to improve food security along with the challenges posed by expansion of urban and coastal stakeholders into nearshore and sheltered marine waters. This move necessitates innovative solutions for this industry to thrive in high-energy environments. Some innovative research has increased understanding of the physics, hydrodynamics, and structural requirements enabling the development of appropriate systems. The blue mussel (Mytilus edulis), the New Zealand green shell or green lipped mussel (Perna canaliculus), and the Pacific Oyster (Magallana gigas), are the primary targets for commercial exposed bivalve aquaculture. Researchers and industry members are actively advancing existing structures and developing new structures and methodologies for these and alternative high-value species suitable for such conditions. For macroalgae (seaweed) cultivation, such as sugar kelp (Saccharina latissimi), oar weed (Laminaria digitata), or kelp sp. (Ecklonia sp.), longline systems are commonly used, but further development is needed to withstand fully exposed environments and improve productivity and efficiency. In marine finfish aquaculture, three primary design categories for open ocean net pens are identified: flexible gravity pens, rigid megastructures, closed pens, and submersible pens. As aquaculture ventures into more demanding environments, a concerted focus on operational efficiency is imperative. This publication considers the commercial and research progress relating to the requirements of aquaculture’s expansion into exposed seas, with a particular focus on the cultivation of bivalves, macroalgae, and marine finfish cultivation technologies and structural developments.

Seaweed cultivation systems suitable for offshore and exposed locations have the potential to enable expansion of global seaweed production to levels capable of substantially supplementing or offsetting terrestrial agriculture. A demonstration scale, experimental seaweed cultivation system (farm) intended to withstand exposed ocean environments was designed, deployed, planted with kelp (a type of seaweed), monitored and decommissioned. Objectives for the field program included: [1] observation of the farm’s behavior and survivability in exposed ocean conditions, [2] demonstration of novel farm system design features and component technologies, and [3] evaluation of farm operability. Novel design features included a lattice mooring system geometry, multi-shaft helical anchors, and the use of fiberglass rod as a replacement for rope anchor lines and kelp growth substrate in order to mitigate the risk of marine animal entanglement. New hardware was developed for transmitting tension loads to and from fiberglass rods, enabling their use in the farm. A numerical model was used in the design stage to simulate the farm in ocean conditions. Analysis results were used to specify farm components, evaluate sensitivities to installation precision, identify potential issues with component interaction, consider operational constraints and investigate the implications of single point failures. The farm was installed at a Gulf of Maine, USA site and planted with Saccharina latissima (sugar kelp) in November 2021 through January 2022 and monitored for one growth season. Kelp was sampled 3 times and met-ocean conditions were measured throughout the season. Kelp was harvested in May 2022 and the structure was removed June 2022. Recovered components were inspected for wear. The farm survived a series of storm events with significant wave heights greater than 2m and at least one storm with a maximum wave height of 5.9m. The farm system experienced only minor corrosion, wear and damage. Farm operations revealed the need for improved accessibility, tension control and anchor placement accuracy. Observations and tests revealed relatively poor kelp holdfast attachment to the fiberglass rope replacement. Nonetheless, demonstration results suggest that the experimental farming system design was suitable for use in exposed settings.

When moving from a very sheltered aquaculture site to a very exposed oceanic aquaculture site, the energy increases proportionally in a continuum. Lojek et al. (in review) considered the primary influential parameters (water current, wave height, wave period, wavelength and water depth) which influence the species, structure, technology, methods, and operational aspects of any aquaculture endeavour and investigated six possible indices which cover these variables. Added to advanced computer modelling, assisted by detailed and constant environmental monitoring, it may be possible to refine site selection, structure selection and design, species selection, equipment and logistic requirements and health and safety requirements. This manuscript has selected two indicative indices: Specific Exposure Energy (SEE) index and Exposure Velocity (EV) index from the potential equations provided by Lojek et al. (in review) and compared them with known operational aquaculture sites highlighting present structural capability and limitations. The two indices are also utilized to reflect on their suitability for assessing sample sites with respect to biological, technological, operational or maintenance aspects of aquaculture activities. The indices have shown themselves to be useful tools in the general assessment of the energy that will influence the species and structure selection at potential aquaculture sites. This information can help prospective fish farmers characterize their sites concisely and accurately to consultants, regulators, equipment vendors, and insurance brokers.

Sustainable aquaculture in nearshore waters faces challenges such as stakeholder conflicts, environmental pollution, and spatial constraints. Offshore aquaculture offers a promising solution but requires robust engineering design to withstand extreme weather conditions. This study develops the environmental conditions essential for engineering the design of a continuous mussel dropper system in New England offshore waters. A potential farm location was identified using criteria including water depth, federal boundaries, seafloor suitability, farm size, and proximity to ports, based on bathymetric and sedimentary maps. Historical data from five wave monitoring stations and two current velocity stations were analyzed to model extreme environmental conditions, as waves and currents pose primary threats. The extreme wave and current conditions are modeled using the Weibull distribution, on the annual maximum hourly significant wave height data and the largest 0.3 % of current speeds. A newly proposed method combining Spalding's wall function with a fourth-order polynomial is used to enhance the current profile analysis. Additionally, a joint probability density function was developed for wave height and current velocity at a specific depth, providing insights into wave height, period, and wavelength for various return periods such as 10, 25, 50, and 100 years. The results suggest a 10-yr wave of 8 m significant wave height and a current speed of 1.68 m/s, while a 50-yr values are 9.4 m and 1.96 m/s respectively. These findings offer critical data on extreme wave and current conditions in New England's offshore waters, providing practical guidance for the engineering design of offshore mussel farms. This research advances offshore mussel farming and benefits the development of all types of offshore aquaculture systems.

The term “offshore” with regards to aquaculture has hitherto encompassed various perspectives, including technology, geographic location, legal jurisdiction, and more. To resolve the ambiguity in this term and understand its implications for current and future aquaculture development, “offshore” should be resolved into two separate metrics: distance from shore and energy exposure. The United Nations Convention on the Law of the Sea (UNCLOS) distinguishes between internal waters, territorial sea, contiguous zone, exclusive economic zone (EEZ), and the high seas, but currently has no precise definition for “offshore” in its provisions, and therefore no applicable laws pertaining to “offshore” aquaculture. Regulating a multi-technology aquaculture sector may require integrating new spatial concepts into the law rather than merely adapting and extending current regulatory designs to include new production concepts. The metrics of distance from shore and exposure are seen as a range rather than a specific threshold, allowing for a continuum. Distance from shore is readily quantified as a distance from a baseline. To rigorously quantify the exposure, the influence and interactions of oceanic parameters (water depth, water current, and wave height and period) we utilized to generate six indices. These oceanic parameters are seen as the main contributions which influence the physical and some biological parameters required for site, species, and technology selection. Four shellfish, three seaweed, and three finfish sites along with 20 potential aquaculture sites were examined using the indices in association with the energy index to determine tolerances of the structures and their ability to cultivate their relevant species. Two indices, Specific Exposure Energy (SEE) and Exposure Velocity (EV), were selected for utilization in the analysis of sites based on their ease of use and applicability. The interaction between the energy indices and various aspects of farm operations and performance were explored. The indices developed and used in the case studies presented have been shown to be useful tools in the general assessment of the energy that will influence the species and equipment selection at potential aquaculture sites. The indices do not provide a definitive answer as to the potential financial success of a site as this requires other inputs relating to infrastructure costs, annual production, distance from port, sales strategy, etc. However, the Specific Exposure Energy index creates a useful tool to describe site energy and be comprehensible to a wide range of stakeholders. We recommend the SEE index be adopted as the predominant tool to communicate the exposure level of aquaculture sites.

The terms “offshore” and “open ocean” have been used to describe aquaculture sites that are further from the coast or in higher energy environments. Neither term has been clearly defined in the scientific literature nor in a legal context, and the terms are often used interchangeably. These and other related terms (for example “exposed”, “high-energy”) variously refer to aspects of a site such as the geographic distance from shore or infrastructure, the level of exposure to large waves and strong currents, the geographic fetch, the water depth, or some combination of these parameters. The ICES Working Group (ICES, 2024) on Open Ocean Aquaculture (WGOOA) therefore identified a need to define the terminology to reduce ambiguity for these types of aquaculture sites or more precisely, to: (1) promote a common understanding and avoid misuse for different classifications; (2) enable regulators to identify the characteristics of a marine site; (3) allow farmers to be able to assess or quantitatively compare sites for development; (4) equip developers and producers to identify operational parameters in which the equipment and vessels will need to operate; (5) provide insurers and investors with the terminology to consistently assess risk and premiums; and (6) circumvent the emergence of narratives that root in different cognitive interpretations of the terminology in public discourse. This paper describes the evolution of the use of the term “offshore aquaculture” and define the most relevant parameters to shift to a more definitive and robust term “exposed aquaculture” that can inherently relay clearer information. Adoption of this more definitive definition of “exposed” will allow the user to define a site with more than just distance from shore. Key differences and the importance of these terms are discussed that affect various interest groups. Follow-up articles in this compilation from scientific members of the WGOOA as well as other scientists outside ICES are incorporated that develop a set of definitions and a rigorous exposure index.

Over the last several decades, the commercial fishing fleet in New England has been subjected to increasingly restrictive management measures established to rebuild declining stocks. This has limited fishing opportunities and significantly reduced the inshore small vessel fleet. To help support New Hampshire (NH) commercial fishermen, an extension program was developed by the University of New Hampshire (UNH) and NH Sea Grant to train fishers on small-scale integrated multi-trophic aquaculture (IMTA) growing steelhead trout, blue mussels, and sugar kelp together, with the goal of providing alternative income sources and increasing local food production without adding significant levels of nitrogen to the environment. A total of 416 kg of steelhead trout, 3072 kg of blue mussels, and 638 kg of sugar kelp were produced in this study. The steelhead trout released an estimated 25.1 kg of N into the environment, while the mussels and kelp together extracted an estimated 41.5 kg N for a net reduction of similar to 16.4 kg N from the ecosystem. There was no observed negative impact on local water quality at any point during the trial. Overall, this program demonstrated a culture method that can positively impact the ecosystem, while providing the fishermen with a new skill set that they could adopt either part time or full time, to provide additional income.

An experimental kelp farming system for exposed ocean conditions was designed, deployed, planted with kelp and instrumented for evaluation of its dynamic response to ocean waves, tides, and currents. The farm featured a novel "lattice" mooring design and anchor lines and cultivation lines (horizontal lines used as kelp growth substrate) made of fiberglass rods. The farm was deployed at a site in Saco Bay, Maine with 13 m (MLLW) water depth. There the farm was exposed to waves with heights up to 5.9 m. Anchor line tension, tide and wave height time series were gathered and processed into response amplitude operators (RAOs) and least squared error linear regression models enabling recognition of meaningful patterns between the forcing factors and the mooring response. Mean mooring line tensions were shown to increase nonlinearly with tide. Anchor line tension response amplitudes were shown to exhibit high sensitivity to both low and high frequency wave forcing. Numerical free-release test simulations suggested natural frequencies in heave of 0.91 Hz, indicating that tension response sensitivities at high frequency could be the result of resonance. Low frequency tension response disproportionate to the low frequency wave forcing could be explained by wave forcing on kelp cultivation arrays modulated by wave group envelopes. Instances of high magnitude, potentially damaging peak tensions, deemed shock loads, were prevalent in most load cases. Anchor line tension dynamics including RAO and shock load magnitudes were shown to be sensitive to mooring stiffness (ratio of tension to resulting elongation) and, in some cases, significant wave amplitude. Patterns of anchor line response indicated that additional mooring elasticity or geometric compliance and use of floatation with less sensitivity to high frequency waves could help avoid the cause of and costly consequences of amplified high frequency loading and high amplitude shock loading. RAOs and regression model results also indicated a subdued response in frequencies associated with ocean swell waves, suggesting desirable performance in waves most dominant in extreme storm events. With the proposed improvements, the farm system design suggests merit as a robust and durable macroalgae biomass production platform.

A dynamic numerical modeling approach was used to inform the design process and economic analysis for an offshore kelp farm with a modular structure designed to scale to 1,000 hectares. This modeling approach incorporated finite-element representations of kelp aggregates and was implemented using the software OrcaFlex. А sequence of dynamic loading scenarios corresponding to extreme events observed in the Gulf of Maine (North Atlantic) was developed and implemented in numerical simulations. The simulations were used to predict the overall dynamic response of the considered modular offshore kelp farm and estimate the highest tensions in various farm components including the anchor lines. Both regular and random wave loadings were considered. It was shown that utilization of regular (monochromatic) wave model can lead to significant overprediction of expected tensions and overdesign of the structure under investigation. Identification of the appropriate worst-case loading scenarios allowed for the well justified specification of the farm components and a subsequent techno-economic analysis.

Unless humanity achieves United Nations Sustainable Development Goals (SDGs) by 2030 and restores the relatively stable climate of pre-industrial CO2 levels (as early as 2140), species extinctions, starvation, drought/floods, and violence will exacerbate mass migrations. This paper presents conceptual designs and techno-economic analyses to calculate sustainable limits for growing high-protein seafood and macroalgae-for-biofuel. We review the availability of wet solid waste and outline the mass balance of carbon and plant nutrients passing through a hydrothermal liquefaction process. The paper reviews the availability of dry solid waste and dry biomass for bioenergy with CO2 capture and storage (BECCS) while generating Allam Cycle electricity. Sufficient wet-waste biomass supports quickly building hydrothermal liquefaction facilities. Macroalgae-for-biofuel technology can be developed and straightforwardly implemented on SDG-achieving high protein seafood infrastructure. The analyses indicate a potential for (1) 0.5 billion tonnes/yr of seafood; (2) 20 million barrels/day of biofuel from solid waste; (3) more biocrude oil from macroalgae than current fossil oil; and (4) sequestration of 28 to 38 billion tonnes/yr of bio-CO2. Carbon dioxide removal (CDR) costs are between 25–33% of those for BECCS with pre-2019 technology or the projected cost of air-capture CDR.