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Drag of Clean and Fouled Net Panels--Measurements and Parameterization of Fouling.

Gansel LC, Plew DR, Endresen PC, Olsen AI, Misimi E, Guenther J, Jensen Ø - PLoS ONE (2015)

Bottom Line: A method is proposed to parameterize the effect of fouling in terms of an increase in net solidity.This allows existing numerical methods developed for clean nets to be used to model the effects of biofouling on nets.Measurements with other types of fouling can be added to build a database on effects of the accumulation of different fouling organisms on aquaculture nets.

View Article: PubMed Central - PubMed

Affiliation: Norwegian University of Science and Technology, Department of Marine Technology, Otto Nielsens vei 10, Trondheim, Norway; SINTEF Fisheries and Aquaculture, Department of Aquaculture Technology, Brattørkaia 17C, Trondheim, Norway.

ABSTRACT
Biofouling is a serious problem in marine aquaculture and it has a number of negative impacts including increased forces on aquaculture structures and reduced water exchange across nets. This in turn affects the behavior of fish cages in waves and currents and has an impact on the water volume and quality inside net pens. Even though these negative effects are acknowledged by the research community and governmental institutions, there is limited knowledge about fouling related effects on the flow past nets, and more detailed investigations distinguishing between different fouling types have been called for. This study evaluates the effect of hydroids, an important fouling organism in Norwegian aquaculture, on the forces acting on net panels. Drag forces on clean and fouled nets were measured in a flume tank, and net solidity including effect of fouling were determined using image analysis. The relationship between net solidity and drag was assessed, and it was found that a solidity increase due to hydroids caused less additional drag than a similar increase caused by change in clean net parameters. For solidities tested in this study, the difference in drag force increase could be as high as 43% between fouled and clean nets with same solidity. The relationship between solidity and drag force is well described by exponential functions for clean as well as for fouled nets. A method is proposed to parameterize the effect of fouling in terms of an increase in net solidity. This allows existing numerical methods developed for clean nets to be used to model the effects of biofouling on nets. Measurements with other types of fouling can be added to build a database on effects of the accumulation of different fouling organisms on aquaculture nets.

No MeSH data available.


Hydroid fouling on aquaculture nets.The images show net panels on the same fish farm, but at different times with approximately one month between the images. Hydroids found on Norwegian salmon cages have bright pink hydranths (a), but on some nets, probably mostly in late autumn and early winter, hydranths may be lost or retracted (b).
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pone.0131051.g001: Hydroid fouling on aquaculture nets.The images show net panels on the same fish farm, but at different times with approximately one month between the images. Hydroids found on Norwegian salmon cages have bright pink hydranths (a), but on some nets, probably mostly in late autumn and early winter, hydranths may be lost or retracted (b).

Mentions: The forces on fouled and clean nets were measured in a low-turbulence recirculation flume tank. The tank was 13 m long, 0.6 m wide and 0.5 m deep. The biofouling on nets consisted mostly of hydroids (see also section 'Clean nets and accumulation of biofouling on net panels') and the water in the flume tank was freshwater. In a pre-test, most hydroids lost their hydranths within seconds after their submergence in freshwater, which may result in changes in the drag force of fouled nets. The hydranths are the pink parts on top of the stems of hydroids (hydrocaulus) in Fig 1a. Therefore, all nets were kept in freshwater for a few minutes to remove the hydranths from the hydroids before they were mounted in the flume tank. Only the hydranths were lost prior to the measurements, but the hydrocauli of hydroids stayed intact. Hydroids are found in different developmental stages on Norwegian aquaculture nets. Two examples from hydroid-fouling on coated salmon nets samples that were submerged at a commercial Atlantic salmon farm in southern Norway are shown in Fig 1. The picture in Fig 1a was taken in August 2011 and here the hydroids have bright pink hydranths. Most hydroids in Fig 1b, taken in late October 2011, do not have hydranths. Pyefinch and Downing [16] found that hydroids may lose and re-grow hydranths in the sea. The results from this study describe effects of net fouling with hydroids in a state similar to that shown in Fig 1b. However, they may also help to estimate effects of any filamentous, flexible fouling in the hydroid size range (the length scale is centimeters and the diameter scale is millimeters).


Drag of Clean and Fouled Net Panels--Measurements and Parameterization of Fouling.

Gansel LC, Plew DR, Endresen PC, Olsen AI, Misimi E, Guenther J, Jensen Ø - PLoS ONE (2015)

Hydroid fouling on aquaculture nets.The images show net panels on the same fish farm, but at different times with approximately one month between the images. Hydroids found on Norwegian salmon cages have bright pink hydranths (a), but on some nets, probably mostly in late autumn and early winter, hydranths may be lost or retracted (b).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4495041&req=5

pone.0131051.g001: Hydroid fouling on aquaculture nets.The images show net panels on the same fish farm, but at different times with approximately one month between the images. Hydroids found on Norwegian salmon cages have bright pink hydranths (a), but on some nets, probably mostly in late autumn and early winter, hydranths may be lost or retracted (b).
Mentions: The forces on fouled and clean nets were measured in a low-turbulence recirculation flume tank. The tank was 13 m long, 0.6 m wide and 0.5 m deep. The biofouling on nets consisted mostly of hydroids (see also section 'Clean nets and accumulation of biofouling on net panels') and the water in the flume tank was freshwater. In a pre-test, most hydroids lost their hydranths within seconds after their submergence in freshwater, which may result in changes in the drag force of fouled nets. The hydranths are the pink parts on top of the stems of hydroids (hydrocaulus) in Fig 1a. Therefore, all nets were kept in freshwater for a few minutes to remove the hydranths from the hydroids before they were mounted in the flume tank. Only the hydranths were lost prior to the measurements, but the hydrocauli of hydroids stayed intact. Hydroids are found in different developmental stages on Norwegian aquaculture nets. Two examples from hydroid-fouling on coated salmon nets samples that were submerged at a commercial Atlantic salmon farm in southern Norway are shown in Fig 1. The picture in Fig 1a was taken in August 2011 and here the hydroids have bright pink hydranths. Most hydroids in Fig 1b, taken in late October 2011, do not have hydranths. Pyefinch and Downing [16] found that hydroids may lose and re-grow hydranths in the sea. The results from this study describe effects of net fouling with hydroids in a state similar to that shown in Fig 1b. However, they may also help to estimate effects of any filamentous, flexible fouling in the hydroid size range (the length scale is centimeters and the diameter scale is millimeters).

Bottom Line: A method is proposed to parameterize the effect of fouling in terms of an increase in net solidity.This allows existing numerical methods developed for clean nets to be used to model the effects of biofouling on nets.Measurements with other types of fouling can be added to build a database on effects of the accumulation of different fouling organisms on aquaculture nets.

View Article: PubMed Central - PubMed

Affiliation: Norwegian University of Science and Technology, Department of Marine Technology, Otto Nielsens vei 10, Trondheim, Norway; SINTEF Fisheries and Aquaculture, Department of Aquaculture Technology, Brattørkaia 17C, Trondheim, Norway.

ABSTRACT
Biofouling is a serious problem in marine aquaculture and it has a number of negative impacts including increased forces on aquaculture structures and reduced water exchange across nets. This in turn affects the behavior of fish cages in waves and currents and has an impact on the water volume and quality inside net pens. Even though these negative effects are acknowledged by the research community and governmental institutions, there is limited knowledge about fouling related effects on the flow past nets, and more detailed investigations distinguishing between different fouling types have been called for. This study evaluates the effect of hydroids, an important fouling organism in Norwegian aquaculture, on the forces acting on net panels. Drag forces on clean and fouled nets were measured in a flume tank, and net solidity including effect of fouling were determined using image analysis. The relationship between net solidity and drag was assessed, and it was found that a solidity increase due to hydroids caused less additional drag than a similar increase caused by change in clean net parameters. For solidities tested in this study, the difference in drag force increase could be as high as 43% between fouled and clean nets with same solidity. The relationship between solidity and drag force is well described by exponential functions for clean as well as for fouled nets. A method is proposed to parameterize the effect of fouling in terms of an increase in net solidity. This allows existing numerical methods developed for clean nets to be used to model the effects of biofouling on nets. Measurements with other types of fouling can be added to build a database on effects of the accumulation of different fouling organisms on aquaculture nets.

No MeSH data available.