Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Comparisons of echo-integration performance from two multiplexed echosounders
Macaulay, Gavin J. ; Scoulding, Ben ; Ona, Egil ; Fässler, Sascha M.M. - \ 2018
ICES Journal of Marine Science (2018). - ISSN 1054-3139 - 10 p.
Acoustic survey - echo-integration - echosounder - EK60 - EK80 - intercomparison
A time-series of acoustically derived aquatic biomass estimates relies on the acoustic equipment maintaining the same performance throughout the time-series. This is normally achieved through a regular calibration process. When the acoustic equipment changes it is necessary to verify that the new equipment produces a similar result to the old equipment, otherwise an unknown bias can be introduced into the time-series. The commonly used Simrad EK60 echosounder has been superseded by the Simrad EK80 echosounder and the performance of these two scientific echosounder systems was compared using interleaved pinging through the same transducer. This was repeated for multiple transducer frequencies (18, 38, 70, 120, and 200 kHz) and from two vessels (Norway’s G.O. Sars in the North Sea and The Netherlands’ Tridens in the Northeast Atlantic Ocean). The broadband facility of the EK80 was not used. Regressions of the grid-integrated backscatter from the two systems were
highly linear. The difference in area backscattering coefficients in typical survey conditions was less than 0.6 dB (12%) at the main survey frequency of 38 kHz. In most conventional fish acoustic surveys, the observed differences are less than other sources of survey bias and uncertainty.
Towards acoustic monitoring of a mixed demersal fishery based on commercial data: The case of the Northern Demersal Scalefish Fishery (Western Australia)
Gastauer, Sven ; Scoulding, Ben ; Parsons, Miles - \ 2017
Fisheries Research 195 (2017). - ISSN 0165-7836 - p. 91 - 104.
Ongoing monitoring of complex, mixed species environments is a challenging task. In this study, the potential of acoustic and catch data collected aboard a commercial fishing vessel, in combination with geostatistical variance estimates, are explored as a means to derive information on the distribution and abundance of key species groups within selected fishing regions. The FV Carolina M, a trap fishing vessel which operates in waters off Broome, Western Australia, in the Northern Demersal Scalefish Fishery, was equipped with Simrad ES70 echosounders, operated at 38 and 120 kHz. Optical recordings of catch were also obtained, in addition to the acoustic data, during routine fishing operations in 2014. Three regions, where both optical and acoustic datasets were available, were selected for analysis. Geostatistical conditional simulations were used to combine acoustic density information with species composition proportions and length distributions within the catch. For each of the input datasets 250 simulations were conducted, from which individual and combined sampling CVs were derived. Conversion of acoustic densities into abundance estimates was achieved through application of target strength to length relationships (TS-L). Where TS-L was unavailable in the literature for a particular species it was estimated through a Kirchhoff-ray mode model. TS-L equations were estimated for rankin cod (Epinephelus multinotatus)(TSRC = 20 log10(L) − 79.6), triggerfish (Balistidae) (TSTF = 20 log10(L) − 77.7) and spangled emperor (Lethrinus nebulosus) (TSSE = 20 log10(L) − 70.8) at 38 kHz. Sampling error was found to be generally low for catch proportions (<12%) and acoustic densities (<10%). Total sampling error CV for species group abundances within each of the three regions was 9%–38%, which is similar to typical estimates reported for acoustic surveys.
An Unsupervised Acoustic Description of Fish Schools and the Seabed in Three Fishing Regions Within the Northern Demersal Scalefish Fishery (NDSF, Western Australia)
Gastauer, Sven ; Scoulding, Ben ; Parsons, Miles - \ 2017
Acoustics Australia 45 (2017)2. - ISSN 0814-6039 - p. 363 - 380.
Fisheries acoustics is now a standard tool for monitoring marine organisms. Another use of active-acoustics techniques is the potential to qualitatively describe fish school and seafloor characteristics or the distribution of fish density hotspots. Here, we use a geostatistical approach to describe the distribution of acoustic density hotspots within three fishing regions of the Northern Demersal Scalefish Fishery in Western Australia. This revealed a patchy distribution of hotspots within the three regions, covering almost half of the total areas. Energetic, geometric and bathymetric descriptors of acoustically identified fish schools were clustered using robust sparse k-means clustering with a Clest algorithm to determine the ideal number of clusters. Identified clusters were mainly defined by the energetic component of the school. Seabed descriptors considered were depth, roughness, first bottom length, maximum Sv, kurtosis, skewness and bottom rise time. The ideal number of bottom clusters (maximisation rule with D-Index, Hubert Score and Weighted Sum of Squares), following the majority rule, was three. Cluster 1 (mainly driven by depth) was the sole type present in Region 1, Cluster 2 (mainly driven by roughness and maximum Sv) dominated Region 3, while Region 2 was split up almost equally between Cluster 2 and 3. Detection of indicator species for the three seabed clusters revealed that the selected clusters could be related to biological information. Goldband snapper and miscellaneous fish were indicators for Cluster 1; Cods, Lethrinids, Red Emperor and other Lutjanids were linked with Cluster 2, while Rankin Cod and Triggerfish were indicators for Cluster 3.
Estimates of variability of goldband snapper target strength and biomass in three fishing regions within the Northern Demersal Scalefish Fishery (Western Australia)
Gastauer, Sven ; Scoulding, Ben ; Parsons, Miles - \ 2017
Fisheries Research 193 (2017). - ISSN 0165-7836 - p. 250 - 262.
Error estimates - Fisheries acoustics - Fishing vessel - Geostatistics - Goldband snapper - NDSF - Target strength
Goldband snapper (Pristipomoides multidens) is an ecologically and economically important species in the Northern Demersal Scalefish Fishery (NDSF). The Carolina M, a trap fishing vessel operating in the NDSF, was equipped with Simrad ES70 echosounders, operated at 38 and 120 kHz. In 2014 acoustic data, in combination with optical recordings of the catch, were opportunistically collected during routine fishing operations. In December 2014 pure, low density goldband snapper schools were observed on the echograms. In situ target strength (TS) estimates were derived and linked to length distributions of catch information with the curve fitting method. Estimated TS-Length (L) at 38 kHz was 20.1 log10(L)-70.5 and 16.4 log10(L)-77 at 120 kHz. Three fishing grounds, where near simultaneously recorded acoustic and optical information was available were selected. Fish school densities observed within the 38 kHz acoustic data were disaggregated according to catch proportions using kriging. Goldband snapper density estimates ranged between 9518 individuals per nmi2 in the high-density fishing region and 2512 and 945 individuals per nmi2 in the two low density fishing regions. Sampling variance was estimated using geostatistics (coefficient of variance, CV = 10–20.9%). Other errors considered were signal-to-noise ratio (CV < 1%), variation in the acoustic signal due to fluctuations in temperature and salinity (CV = 0.5–1.15%), effects of diurnal vertical migration and variability of catch information (CV = 1.2–2%). A total CV of 28.2–50.6% was estimated for all considered sources, for the three fishing regions.
Effects of variable mean target strength on estimates of abundance: the case of Atlantic mackerel (Scomber scombrus)
Scoulding, Ben ; Gastauer, Sven ; Maclennan, David N. ; Fassler, S.M.M. ; Copland, Phillip ; Fernandes, Paul G. - \ 2016
ICES Journal of Marine Science 74 (2016)3. - ISSN 1054-3139 - p. 822 - 831.
Atlantic mackerel - biomass estimation - geostatistics - scattering properties - target strength
Atlantic mackerel Scomber scombrus is a small pelagic, migratory fish which supports commercial fisheries. These fish school and are detectable using echosounders, yet fishery-independent estimates of their abundance in the North East Atlantic do not consider acoustic data. Accurate estimates of mean target strength (TS) are presently limiting echo-integration surveys from providing useful estimates of Atlantic mackerel abundance and distribution. This study provides TS estimates for in situ mackerel from multi-frequency split-beam echosounder measurements. TS equals 52.79 dB at 18 kHz, 59.60 dB at 38 kHz, 55.63 dB at 120 kHz, and 53.58 dB at 200 kHz, for a mean mackerel
total length¼33.3 cm. These values differ from those currently assumed for this the sensitivity of acoustically estimated mackerel biomass around the Shetland Islands, Scotland, in 2014, to various estimates of TS. Confidence limits were obtained using geostatistics accounting for coverage and spatial autocorrelation. Stock biomasses, estimated from 38 and 200 kHz data, differed by 10.5%, and stock distributions were similar to each other and to the estimates from an independent stock assessment. Because mackerel backscatter at 38 kHz is dominated by echoes from the flesh and may have similarities to echoes from fish with swimbladders, and backscatter at 200 kHz is dominated by relatively stable echoes from the backbone, we recommend using 200 kHz data for
estimates of Atlantic mackerel biomass.
Additional evidence for fisheries acoustics : Small cameras and angling gear provide tilt angle distributions and other relevant data for mackerel surveys
Fernandes, Paul G. ; Copland, Phillip ; Garcia, Rafael ; Nicosevici, Tudor ; Scoulding, Ben - \ 2016
ICES Journal of Marine Science 73 (2016)8. - ISSN 1054-3139 - p. 2009 - 2019.
acoustic surveys - ground truth - mackerel - rod and line - tilt angle - video

Fisheries acoustics surveys are effective tools in marine resource assessment and marine ecology. Significant advances have occurred in recent years with the application of multiple and broadband frequencies to enable remote species identification. There is, however, still the need to obtain additional evidence for identification, and the estimation of the size and tilt angle distribution of fish, which influences their acoustic target strength. The former two requirements are usually met by obtaining simultaneous net samples: there are limited, if any, recognized successful techniques for the latter. Here, two alternative tools for obtaining evidence for all three requirements are examined: angling gear and small video cameras. These tools were deployed during surveys of Atlantic mackerel (Scomber scombrus). In 2014, angling was actually more efficient than pelagic trawling (the standard technique) and over two survey periods (2012 and 2014) provided length frequency distributions that were not significantly different. A small video camera was deployed into mackerel schools, providing species identification and fish orientation. Image analysis was then applied, producing tilt-angle distributions of free swimming wild mackerel for the first time. Mean tilt angles from three deployments were very variable with 95% of observations falling between -70° and 39° with evidence of a multinomial frequency distribution. A video equipped lander was also deployed onto the type of rocky seabed where deployment of a trawl would be impossible: this confirmed the presence of Norway pout and suggested it was the dominant scatterer on this type of seabed. These techniques are complementary to traditional trawling methods, but provide additional insights into fish behaviour whilst satisfying standard requirements of identification and supplying biological samples. Crucially, the small cameras deployed approximate the size of the animals under observation and allow for measurement of behaviour (specifically tilt) that are more likely to represent those conditions encountered during surveying.

Target strength estimates of red emperor (Lutjanus sebae) with Bayesian parameter calibration
Gastauer, Sven ; Scoulding, Ben ; Fassler, Sascha ; Benden, Daniel P.L.D. ; Parsons, Miles - \ 2016
Aquatic Living Resources 29 (2016)3. - ISSN 0990-7440
Bayesian inference - Fisheries acoustics - KRM - Lutjanus sebae - Target Strength - Vessel of opportunity

Red emperor (Lutjanus sebae) is a long-lived tropical demersal snapper which is widely distributed in the Western Pacific and Indian Ocean. Despite the commercial and recreational importance of the species for the Northern Demersal Scalefish Fishery off the Northwest coast of Western Australia, we still lack a thorough understanding of its distribution and abundance in the area. To better understand the acoustic scattering properties of red emperor its acoustic backscattering characteristics were modelled based on swimbladder and body morphology, determined using computed tomography scans. A Kirchhoff-ray mode approximation was coupled with empirical (ex situ) measurements of target strength (TS) obtained from a 38 and 120 kHz split-beam echosounder on board a fishing vessel. Bayesian methods were used for model parameter calibration, which provided uncertainty estimates for some of the TS-model parameters. The derived TS-length relationships were 19.7log 10(L)-75.5 (C.I. 5.9 dB) at 120 kHz and 14.6 log10(L)-64.9 (C.I. 5.8 dB) at 38 kHz. The study demonstrated that small commercial fishing vessels can be used to conduct ex situ experiments and target strength modelling can be effectively based on computer tomography scans. This relatively low cost approach could be applied to other species.

The distribution of blue whiting west of the British Isles and Ireland
Gastauer, Sven ; Fassler, Sascha ; O'Donnell, Ciaran ; Høines, Åge ; Jakobsen, Jan Arge ; Krysov, Alexander I. ; Smith, Leon ; Tangen, Øyvind ; Anthonypillai, Valantine ; Mortensen, Ebba ; Armstrong, Eric ; Schaber, Matthias ; Scoulding, Ben - \ 2016
Fisheries Research 183 (2016). - ISSN 0165-7836 - p. 32 - 43.
Acoustic survey - Blue whiting - Geostatistics - Spatial indices

Northern blue whiting is a small abundant pelagic gadoid that is widely distributed in the northeast Atlantic and one of the most commercially valuable species west of the British Isles and Ireland. Over the last two decades the northeast Atlantic stock has undergone dramatic changes in abundance. The stock size decreased dramatically from 2007 to 2011, but has since shown signs of recovery. Changes in recruitment levels have occurred almost simultaneously with unusual changes in the north Atlantic ecosystem and oceanography. These links may suggest a causal linkage and the possibility of improving our understanding of the recruitment and spawning stock distribution. Here we use a set of geostatistical indices to describe the temporal and spatial patterns of the northeast Atlantic blue whiting stock in spring of 2006-2014. Geostatistical indices were computed to investigate changes in the spatial distribution, dynamics and variability of the stock in terms of density and location. Indices revealed 3 different distribution patterns over the time series. Main concentrations were either found around Rockall (first years), west of the Hebrides (2008-2013) or in the southern survey area (2014). The distribution was found to be age structured, with young blue whiting mainly concentrated in shallower areas (1000 m). A general additive mixed model (GAMM) was used to model the distribution of blue whiting according to environmental conditions and location.

VIP report "Use of new broadband echosounder" : Techniques for improved ocean imaging and selectivity in pelagic fisheries
Fassler, S.M.M. ; Scoulding, B.C. ; Burggraaf, D. ; Haan, D. de; Quesson, Benoit ; Sande, Jeroen van de; Beerens, Peter - \ 2015
IMARES (Report / IMARES C171/15) - 100 p.
pelagic fishery - marine fisheries - underwater acoustics - fish stocks - bycatch - fishery resources - fishery management - pelagische visserij - zeevisserij - onderwaterakoestiek - visstand - bijvangst - visbestand - visserijbeheer
North Sea Herring and Pelagic Ecosystem Survey (HERAS) report for R/V "TRIDENS" 22 June - 17 July 2015
Couperus, A.S. ; Fassler, S.M.M. ; Scoulding, B.C. - \ 2015
IJmuiden : IMARES (Report / IMARES 15.015) - 30 p.
herrings - surveys - fish stocks - marine fisheries - acoustic tracking - fishery resources - north sea - haringen - karteringen - visstand - zeevisserij - akoestisch sporen - visbestand - noordzee
Cruise report hydroacoustic survey for blue whiting (Micromesistius poutassou) with F.R.V. Tridens (BWHTS) 23 March - 7 April 2015
Scoulding, B.C. - \ 2015
IJmuiden : IMARES (Report / IMARES Wageningen UR 15.008) - 20
micromestistius poutassou - onderwaterakoestiek - noordoost atlantische oceaan - eu regelingen - visbestand - ruimtelijke verdeling - underwater acoustics - northeast atlantic - eu regulations - fishery resources - spatial distribution
This survey is part of the ICES coordinated international hydro acoustic survey for blue whiting which is carried out yearly in March/April. The other participating countries are the Faroe Islands, Ireland, Norway and Russia. IMARES, Institute for Marine Resources & Ecosystem Studies, part of Wageningen University and Research, has participated in the international North-East Atlantic hydro acoustic survey for blue whiting since 2004. The survey is part of the EU Data Collection Framework. The aim of this survey is to provide an abundance estimate of the whole North-East Atlantic blue whiting population and to determine the spatial distribution at this time of year. This estimate is used as a tuning index by the ICES Working Group on Widely Distributed Stocks (WGWIDE) to determine the size of the population. In this report the results are presented of the survey west of Ireland, carried out by FRV “Tridens”. A secondary objective during the survey is to gather information on the distribution of non-commercial mesopelagic species.
Target strengths of two abundant mesopelagic fish species
Scoulding, B.C. ; Chu, D. ; Ona, E. ; Fernandes, P.G. - \ 2015
Journal of the Acoustical Society of America 137 (2015)2. - ISSN 0001-4966 - p. 989 - 1000.
lanternfishes family myctophidae - diel vertical migration - in-situ - acoustic scattering - swimbladder morphology - sound scattering - walleye pollock - behavior - length - identification
Mesopelagic fish of the Myctophidae and Sternoptychidae families dominate the biomass of the oceanic deep scattering layers and, therefore, have important ecological roles within these ecosystems. Interest in the commercial exploitation of these fish is growing, so the development of techniques for estimating their abundance, distribution and, ultimately, sustainable exploitation are essential. The acoustic backscattering characteristics for two size classes of Maurolicus muelleri and Benthosema glaciale are reported here based on swimbladder morphology derived from digitized soft x-ray images, and empirical (in situ) measurements of target strength (TS) derived from an acoustic survey in a Norwegian Sea. A backscattering model based on a gas-filled prolate spheroid was used to predict the theoretical TS for both species across a frequency range between 0 and 250 kHz. Sensitivity analyses of the TS model to the modeling parameters indicate that TS is rather sensitive to the viscosity, swimbladder volume ratio, and tilt, which can result in substantial changes to the TS. Theoretical TS predictions close to the resonance frequency were in good agreement (±2¿dB) with mean in situ TS derived from the areas acoustically surveyed that were spatially and temporally consistent with the trawl information for both species.
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