An underwater laser stripe seabed profiler to measure the physical impact of towed gear components on the seabed

O’Neill, Fiona; Summerbell, K.; Breen, Mike

doi:10.1016/j.fishres.2009.05.012

Cited by 11 publications

(9 citation statements)

References 8 publications

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“…where A ij and B ij are the polynomial coefficients. More details of the calibration procedure can be found in Darboux & Huang () and O'Neill, Summerbell & Breen ().…”

Section: Methodsmentioning

confidence: 99%

“…To determine the true length of the laser line, extracted lines were calibrated from pixels to cm. The calibration technique was based on that developed in soil sciences by Darboux & Huang (2003) and applied to fisheries research by O'Neill, Summerbell & Breen (2009). A grid with 4 cm graduations was placed underwater in the laser plane in front of the sledge (Fig.…”

Section: Complexity Indices Derived From the Laser Linesmentioning

confidence: 99%

“…The real coordinates of each intersection point (in cm) were then related to the (x,y) coordinates of the pixels in the image of the grid using 4th degree polynomial equations (Figs 3 and 4): where A ij and B ij are the polynomial coefficients. More details of the calibration procedure can be found in Darboux & Huang (2003) and O'Neill, Summerbell & Breen (2009).…”

Section: Complexity Indices Derived From the Laser Linesmentioning

confidence: 99%

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A comparison of two techniques for the rapid assessment of marine habitat complexity

et al. 2012

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Monitoring and assessment of the status and distribution of marine seabed habitats is needed to support existing and emerging environmental policy commitments. Traditional monitoring of habitats and associated species using grabs and trawls is costly and labour intensive and might usefully be complemented by cheaper and more readily automated methods that can be used at higher frequencies and/or on larger spatial scales. We develop and apply two methods to measure seabed habitat complexity and demonstrate how they can be used to describe impacts (e.g. fishing gear impacts) and monitor recovery. The first method relies on the analysis of deviations in a laser line projected on the seabed. The second method is based on the pixel value distribution in seabed photographs. We use both methods to quantify the complexity created by different substrates and habitat-forming species and to establish links between habitat complexity and faunal diversity (richness) and abundance. The habitat complexity index calculated with the laser line method provided a reliable index of complexity across a range of habitat types, showing a monotonic increase with coarseness of the substratum and the abundance of sessile epifauna. Pixel value distributions in the photographs did not reflect the increase in complexity due to sessile epifauna but only reflected substratum differences. Results suggested that the laser line method would be suitable for monitoring the effect of disturbance on habitats ranging from gravelly sands to rock, and their subsequent recovery. The photographic method would be better suited to assessing complexity and heterogeneity of the substratum. Both methods complement conventional biological sampling and can be used at higher frequencies and/or on larger spatial scales per unit cost. The laser line method has considerable potential to support demands for frequent monitoring of seabed habitats and human impacts at a range of spatial scales. It is less costly and labour intensive than existing approaches and can be deployed from vessels of many sizes. © 2012 British Ecological Society

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“…where A ij and B ij are the polynomial coefficients. More details of the calibration procedure can be found in Darboux & Huang () and O'Neill, Summerbell & Breen ().…”

Section: Methodsmentioning

confidence: 99%

Section: Complexity Indices Derived From the Laser Linesmentioning

confidence: 99%

Section: Complexity Indices Derived From the Laser Linesmentioning

confidence: 99%

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A comparison of two techniques for the rapid assessment of marine habitat complexity

et al. 2012

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“…There have been many observations of the alteration of the seabed following the passage of towed fishing gears using both acoustic methods (Lucchetti and Sala, 2012;O'Neill et al, 2013b;Palanques et al, 2014;Humborstad et al, 2014;Depestele et al, 2016) and optical methods (O'Neill et al, 2009;Puig et al, 2012;Boulcott et al, 2014).…”

Section: Accepted Manuscriptmentioning

confidence: 99%

The contact drag of towed demersal fishing gear components

O’Neill

Summerbell

Ivanović

2018

Journal of Marine Systems

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The contact demersal towed fishing gears make with the seabed can lead to penetration of the substrate, lateral displacement of the sediment and a pressure field transmitted through the sediment. It will also contribute to the overall drag of the fishing gear. Consequently, there can be environmental effects such as habitat alteration and benthic mortality, and impacts to the fuel efficiency of the fishing operation which will affect emissions of nitrogen oxides, sulphur oxides and greenhouse gases such as CO2. Here we present the results of experimental trials that measure the contact drag of a range of elements that represent some of the components of towed demersal gears that are in contact with the seabed.We show that the contact drag of the gear components depends on their weight, geometry, the type of sediment on which they are towed and whether they are rolling or not. As expected, the contact drag of each gear component increases as its weight increases and the drag of fixed elements is greater than that of the rolling ones. The dependence on aspect ratio is more complex and the drag (per unit area) of narrow cylinders is less than that of wider ones when they roll on the finer sediment or are fixed (not permitted to roll) on the coarser sediment.When they roll on the coarse sediment there is no dependence on aspect ratio. Our results also suggest that fixed components may penetrate the seabed to a lesser depth when they are towed at higher speeds but when they roll there is no such relationship. we measure the contact drag of a range of fishing gear components the contact drag depends on the weight and geometry of a component the contact drag depends on sediment type and whether the components roll or are fixed the contact drag of rolling components does not seem to be dependent on towing speed ACCEPTED MANUSCRIPT

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“…There is limited knowledge about the habitat effects of bottom gillnets partly due to historical focus on active gears, but also because data collection and analysis calls for the development of appropriate innovative assessment methodologies. Several optical or acoustic techniques have been developed as complementary tools to assess the impact of mobile gears on the seabed (Smith et al, 2003;Humborstad et al, 2004;O'Neill et al, 2009;Lucchetti and Sala, 2012;Depestele et al, 2016). However, not all techniques provide a spatial resolution fine enough to assess bottom gillnets.…”

Section: Introductionmentioning

confidence: 99%

Developing and testing a computer vision method to quantify 3D movements of bottom-set gillnets on the seabed

Savina

Krag

Madsen

2017

ICES Journal of Marine Science

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Gillnets are one of the most widely used fishing gears, but there is limited knowledge about their habitat effects, partly due to the lack of methodology to quantify such effects. A stereo imaging method was identified and adapted to quantify the dynamic behaviour of gillnets in-situ. Two cameras took synchronized images of the gear from slightly different perspectives, allowing to estimate the distance from the observation unit to the gear such as in the human 3D vision. The sweeping motion on the seabed and the penetration into the sediment of the leadline of light and heavy commercial bottom gillnets deployed in sandy habitats in the Danish coastal plaice fishery were assessed. The direct physical disruption of the seabed was minimal as the leadline was not penetrating into the seabed. Direct damage to the benthos could however originate from the sweeping movements of the nets, which were found to be higher than usually estimated by experts, up to about 2 m. The sweeping movements were for the most part in the order of magnitude of 10 cm, and resulted in a total swept area per fishing operation lower than any of the hourly swept area estimated for active fishing gears. Whereas the general perception is that heavy gears are more destructive to the habitat, light nets were moving significantly more than heavy ones. The established methodology could be further applied to assess gear dynamic behaviour in situ of other static gears.

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An underwater laser stripe seabed profiler to measure the physical impact of towed gear components on the seabed

Cited by 11 publications

References 8 publications

A comparison of two techniques for the rapid assessment of marine habitat complexity

A comparison of two techniques for the rapid assessment of marine habitat complexity

The contact drag of towed demersal fishing gear components

Developing and testing a computer vision method to quantify 3D movements of bottom-set gillnets on the seabed

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