Biofouling in marine aquaculture is a specific problem where both the target culture species and/or infrastructure are exposed to a diverse array of fouling organisms, with significant production impacts. In shellfish aquaculture the key impact is the direct fouling of stock causing physical damage, mechanical interference, biological competition and environmental modification, while infrastructure is also impacted. In contrast, the key impact in finfish aquaculture is the fouling of infrastructure which restricts water exchange, increases disease risk and causes deformation of cages and structures. Consequently, the economic costs associated with biofouling control are substantial. Conservative estimates are consistently between 5–10% of production costs (equivalent to US$ 1.5 to 3 billion yr−1), illustrating the need for effective mitigation methods and technologies. The control of biofouling in aquaculture is achieved through the avoidance of natural recruitment, physical removal and the use of antifoulants. However, the continued rise and expansion of the aquaculture industry and the increasingly stringent legislation for biocides in food production necessitates the development of innovative antifouling strategies. These must meet environmental, societal, and economic benchmarks while effectively preventing the settlement and growth of resilient multi-species consortia of biofouling organisms.

https://www.tandfonline.com/doi/pdf/10.1080/08927014.2012.700478

The impact and control of biofouling in marine aquaculture: a review

Environmental drivers of Atlantic salmon behaviour in sea-cages: A review

1. Escape of cultured organisms into natural ecosystems may threaten wild populations both ecologically and genetically. In the aquaculture industry, farmed Atlantic salmon (Salmo salar L.) often escape and enter the spawning grounds of wild salmon. We report experiments to assess the competitive and reproductive abilities of fifth-generation farmed salmon and their potential impacts upon wild salmon. 2. The farmed and wild females had similar levels of competitive behaviour; however, they differed in reproductive behaviour and success. Farmed females displayed less breeding behaviour, constructed fewer nests, retained a greater weight of eggs unspawned, were less efficient at nest covering, incurred more nest destruction, and suffered greater egg mortality than wild females. As a result, farmed females had less than one-third of the reproductive success of wild females. 3. The farmed males were even less successful than the farmed females in competition with the wild fish. They were less aggressive, courted less, partook in fewer spawnings, and achieved only an estimated one to three percentage of the reproductive success of the wild males. 4. The farmed males exhibited inappropriate mating behaviour, that led to poor fertilization success, even in the absence of competition with wild males. 5. Adult farmed fish are thus likely to be relatively unsuccessful in natural environments due to a competitive and reproductive inferiority apparently resulting from domestication.

An experimental study of the reproductive behaviour and success of farmed and wild Atlantic salmon (Salmo salar)

Artificial upwelling (AU) is considered a potential means of reducing the accumulation of anthropogenic CO 2 . It has been suggested that AU has significant effects on regional carbon sink or source characteristics, and these effects are strongly influenced by certain technical parameters, the applied region, and the season. In this study, we simulated the power needed to raise the level of deep ocean water (DOW) to designated plume trapping depths in order to evaluate the effect of changing the source DOW depth and the plume trapping depth on carbon sequestration ability and efficiency. A carbon sequestration efficiency index (CSEI) was defined to indicate the carbon sequestration efficiency per unit of power consumption. The results suggested that the CSEI and the carbon sequestration ability exhibit opposite patterns when the DOW depth is increased, indicating that, although raising a lower DOW level can enhance the regional carbon sequestration ability, it is not energy-efficient. Large variations in the CSEI were shown to be associated with different regions, seasons, and AU technical parameters. According to the simulated CSEI values, the northeast past of the Sea of Japan is most suitable for AU, and some regions in the South China Sea are not suitable for increasing carbon sink.

Achieving Highly Efficient Atmospheric CO 2 Uptake by Artificial Upwelling

The anadromous life cycle of Atlantic salmon Salmo salar involves long migrations to novel environments and challenging physiological transformations when moving between salt-free and salt-rich waters. In this article, (1) environmental factors affecting the migration behaviour and survival of smolts and post-smolts during the river, estuarine and early marine phases, (2) how behavioural patterns are linked to survival and (3) how anthropogenic factors affect migration and survival are synthesized and reviewed based on published literature. The timing of the smolt migration is important in determining marine survival. The timing varies among rivers, most likely as a consequence of local adaptations, to ensure sea entry during optimal periods. Smolts and post-smolts swim actively and fast during migration, but in areas with strong currents, their own movements may be overridden by current-induced transport. Progression rates during the early marine migration vary between 0.4 and 3.0 body lengths s(-1) relative to the ground. Reported mortality is 0.3-7.0% (median 2.3) km(-1) during downriver migration, 0.6-36% (median 6.0) km(-1) in estuaries and 0.3-3.4% (median 1.4) km(-1) in coastal areas. Estuaries and river mouths are the sites of the highest mortalities, with predation being a common cause. The mortality rates varied more among studies in estuaries than in rivers and marine areas, which probably reflects the huge variation among estuaries in their characteristics. Behaviour and survival during migration may also be affected by pollution, fish farming, sea lice Lepeophtheirus salmonis, hydropower development and other anthropogenic activities that may be directly lethal, delay migration or have indirect effects by inhibiting migration. Total mortality reported during early marine migration (up to 5-230 km from the river mouths) in the studies available to date varies between 8 and 71%. Hence, the early marine migration is a life stage with high mortalities, due to both natural and human influences. Factors affecting mortality during the smolt and post-smolt stages contribute to determine the abundance of spawner returns. With many S. salar populations in decline, increased mortality at these stages may considerably contribute to limit S. salar production, and the consequences of human-induced mortality at this stage may be severe. Development of management actions to increase survival and fitness at the smolt and post-smolt stages is crucial to re-establish or conserve wild populations.

/pdf/a-critical-life-stage-of-the-atlantic-salmon-salmo-salar-uj6jstbc0n.pdf

A critical life stage of the Atlantic salmon Salmo salar: behaviour and survival during the smolt and initial post-smolt migration.

The escape of fish from aquaculture is perceived as a threat to wild fish populations. The escapes problem is largely caused by technical and operational failures of fish farming equipment. In Norway, 3.93 million Atlantic salmon Salmo salar, 0.98 million rainbow trout Oncorhynchus mykiss and 1.05 million Atlantic cod Gadus morhua escaped from 2001 to 2009. Salmonids primarily escape after structural failures of containment equipment, while a far greater percentage of cod than salmon escape through holes in the nets. Correlative evidence suggests that after the Norwegian technical standard (NS 9415) for sea-cage farms took effect in 2004, the total number of escaped Atlantic salmon declined from >600 000 (2001 to 2006) to <200 000 fish yr -1 (2007 to 2009), despite the total number of salmon held in sea-cages increasing by 44% during this period. No similar decrease in escaped cod has occurred, suggesting that other measures, such as improved netting materials for sea-cages, are required. In addition to escaping as juveniles or adults, cod may reproduce in sea- cages, and thus fertilised eggs escape to the environment. The ecological effects of 'escape through spawning' are unclear, and methods to inhibit escape by this mechanism are being explored. To pre- vent escapes of juvenile and adult fish as sea-cage aquaculture industries develop, we recommend that policy-makers implement a 5 component strategy: (1) establish mandatory reporting of all escape incidents; (2) establish a mechanism to analyse and learn from the mandatory reporting; (3) conduct mandatory, rapid, technical assessments to determine the causes of escape incidents involving more than 10 000 fish; (4) introduce a technical standard for sea-cage aquaculture equipment coupled with an independent mechanism to enforce the standard; and (5) conduct mandatory training of fish farm staff in escape-critical operations and techniques.

https://www.int-res.com/articles/aei2010/1/q001p071.pdf

Escapes of fishes from Norwegian sea-cage aquaculture: causes, consequences and prevention.

Structural analysis of aquaculture net cages in current

Current induced net deformations in full-scale sea-cages for Atlantic salmon (Salmo salar)

https://www.sintef.no/globalassets/upload/fiskeri_og_havbruk/havbruksteknologi/intellistruct/laderfredheim2003.pdf

Dynamic properties of a flexible net sheet in waves and current—A numerical approach

The main goal of this PhD project was to develop a method for non-linear strength analysis of net structures applied in the aquaculture and fishing industries, e.g. net cages and trawls. The work focused on the aquaculture net cage, which was applied in experiments and analyses, and included research to establish knowledge within material properties and failure modes of traditional netting materials for aquaculture. It was chosen to focus on tensile properties and to study elastic and plastic behaviour, fracture, creep behaviour and cod bite damage. The project consisted of three main activities: tensile testing of netting materials, studies and testing of cod bite damage and resistance, and structural analysis of aquaculture net cages. Net cages are built as a system of ropes and netting. They are designed to transfer and carry all major forces through the ropes. Loads from current, waves, weights and handling induce forces in the net cage, which must be dimensioned to withstand this. Analyzing an aquaculture net cage is both complex and time consuming due to non-linear effects, detailed geometry and dynamic loads. The behaviour of the net cage is dominated by very large deformations and displacements, and materials with non-linear properties. There is a need for verified analysis methods and specific guidance on how to reduce the complexity of a net cage analysis. In order to perform a strength analysis of a net cage, it is crucial to know the material properties of the netting material. Traditionally, the material property of major interest for the aquaculture industry has been the tensile breaking strength of netting (mesh) and ropes, and comparatively little focus has been on their detailed stiffness properties and general behaviour prior to fracture. A new test method was established to determine the uniaxial tensile properties of knotless netting materials. It was applied on a variety of netting materials and stress-strain relations were developed. Data on temporary creep properties, recovery of strain post creep and post creep tensile properties of a selection of Raschel knitted netting materials was presented. Post creep tensile testing showed that the length and force at break were not significantly affected by the creep load history. Cod farmers have reported that cod interact with the cage netting through biting and thereby create wear and tear. The nature of the cod bite attack on traditional, multifilament netting materials was described based on studies of cod interaction with traditional knotless netting and resulting fracture damage on netting fibres. Field experiments were performed, subjecting panels of netting to cod bite in commercial cod cages. In addition, a test method was developed to simulate damage on traditional netting from cod bite, and a prototype bite-jig was designed and assembled. It was concluded that netting materials for cod aquaculture must be resistant to cod bite or be repellent or uninteresting for cod. A method for numerical analysis of net cages in constant uniform current was developed and verified for limited solidity, deformations and current velocities. Various new designs for aquaculture net cages were presented and compared to a traditional net cage with regard to stresses in the netting material and deformation of the net cage.

Arne Fredheim

Papers

Escapes of fishes from Norwegian sea-cage aquaculture: causes, consequences and prevention.

Structural analysis of aquaculture net cages in current

Current induced net deformations in full-scale sea-cages for Atlantic salmon (Salmo salar)

Dynamic properties of a flexible net sheet in waves and current—A numerical approach

Technological solutions and operational measures to prevent escapes of Atlantic cod (Gadus morhua) from sea cages