scholarly journals The fuzzy relationship between trawl and acoustic surveys in the North Sea

2005 ◽  
Vol 62 (8) ◽  
pp. 1556-1575 ◽  
Author(s):  
Steven Mackinson ◽  
Jeroen van der Kooij ◽  
Suzanna Neville
Keyword(s):  
Fuzzy Logic ◽  
North Sea ◽  
Environmental Variables ◽  
Acoustic Energy ◽  
Fish Distribution ◽  
Model Free ◽  
The North ◽  
The North Sea ◽  
Acoustic Surveys ◽  
Trawl Catches

Abstract Adding information on the horizontal and vertical distribution of fish both on and between trawl stations is reason enough to perform acoustic surveys routinely in tandem with annual groundfish trawl surveys. Ideally, acoustic and trawl density indices could be combined to maximize information on fish distribution and provide more reliable estimates of stock size. The core of the problem boils down to the question: “how does what we see on an echosounder relate to what we catch in a net?” The fuzzy logic “model-free estimation” approach presented here sidesteps the need to understand specific mechanisms that determine the nature and variability of any relationship between acoustics and trawl catches. Fuzzy logic models that describe and predict the relationship linking acoustics and environmental variables (inputs) with trawl catches (output) are developed, and the sensitivities and robustness of the approach are discussed. In the models examined, the static environmental variables location and depth proved to be better predictors of trawl catches in the North Sea than the acoustic energy in the first 5 m off the bottom. We suggest that finding the “hidden” relationship between acoustics and trawls will require closer attention to partitioning the acoustics data by species/assemblages and understanding the key gear and behavioural differences responsible for producing the high between-gear variability.

scholarly journals Variations in spatial and temporal distribution of Archaea in the North Sea in relation to environmental variables

2007 ◽  
Vol 62 (3) ◽  
pp. 242-257 ◽  
Author(s):  
Lydie Herfort ◽  
Stefan Schouten ◽  
Ben Abbas ◽  
Marcel J. W. Veldhuis ◽  
Marco J. L. Coolen ◽  
...  
Keyword(s):  
North Sea ◽  
Environmental Variables ◽  
Temporal Distribution ◽  
Spatial And Temporal Distribution ◽  
The North ◽  
The North Sea

Geographic variation in the abundance and morphology of the bryozoan Alcyonidium diaphanum (Ctenostomata: Alcyonidiidae) in UK coastal waters

2002 ◽  
Vol 82 (4) ◽  
pp. 529-535 ◽  
Author(s):  
J.S. Porter ◽  
J.R. Ellis ◽  
P.J. Hayward ◽  
S.I. Rogers ◽  
R. Callaway
Keyword(s):  
North Sea ◽  
Coastal Waters ◽  
Additional Data ◽  
Distribution Patterns ◽  
Irish Sea ◽  
Southern North Sea ◽  
The North ◽  
The North Sea ◽  
Catch Rates ◽  
Trawl Catches

The ctenostome bryozoan Alcyonidium diaphanum is widespread and abundant in the coastal waters of England and Wales. It was recorded in 77–90% of beam trawl catches in the eastern English Channel and southern North Sea, and in 53–73% of catches in the Bristol Channel and Irish Sea. The maximum catch rates in these two study areas were 1410 and 751 kg h−1 respectively. Alcyonidium diaphanum was most abundant in the greater Thames Estuary. Additional data from the North Sea indicated that A. diaphanum is widely distributed throughout the southern North Sea. Alcyonidium diaphanum was found intertidally in only seven of 99 locations sampled. Several different morphotypes were observed, ranging from cylindrical to lobate forms. The distribution patterns of various morphotypes are discussed.

scholarly journals Evaluation of the quality of the North Sea herring assessment

2009 ◽  
Vol 66 (8) ◽  
pp. 1814-1822 ◽  
Author(s):  
E. John Simmonds
Keyword(s):  
North Sea ◽  
Management Strategy ◽  
Fishing Mortality ◽  
The North ◽  
Stock Biomass ◽  
Spawning Stock ◽  
The North Sea ◽  
Acoustic Surveys ◽  
One Year

Abstract Simmonds, E. J. 2009. Evaluation of the quality of the North Sea herring assessment. – ICES Journal of Marine Science, 66: 1814–1822. The assessment of North Sea herring has been used to give advice on catch quota for more than 20 years. The data sources comprise acoustic surveys, International Bottom Trawl Surveys, Methot Isaacs–Kidd net post-larval surveys, larval surveys, and catch-at-age data. These sources and their uses are briefly reviewed, and the changes in the weighting attached to each index in the assessment over time are discussed. The performance of the assessment is examined both in historical and analytical retrospectives of spawning–stock biomass and fishing mortality, and in retrospective assessments of numbers by cohort. Increased length of the time-series, the use of a statistical model with appropriate weighting, and a more consistent management strategy have all contributed to the assessment becoming highly stable from one year to the next. The results presented lead to the conclusion that the assessments provide an excellent basis for the management of this stock.

scholarly journals Size-dependent frequency response of sandeel schools

2009 ◽  
Vol 66 (6) ◽  
pp. 1100-1105 ◽  
Author(s):  
Espen Johnsen ◽  
Ronald Pedersen ◽  
Egil Ona
Keyword(s):  
Frequency Response ◽  
North Sea ◽  
Acoustic Frequency ◽  
Independent Variables ◽  
Size Dependent ◽  
Frequency Responses ◽  
The North ◽  
Dependent Frequency ◽  
The North Sea ◽  
Acoustic Surveys

Abstract Johnsen, E., Pedersen, R., and Ona, E. 2009. Size-dependent frequency response of sandeel schools. – ICES Journal of Marine Science, 66: 1100–1105. Annual Norwegian sandeel surveys have been conducted in the North Sea since 2005 to measure the stock of lesser sandeel (Ammodytes marinus). Target identification is often a major challenge in acoustic surveys, and discriminant analyses have been used to separate echoes accurately from schools of herring, mackerel, and sandeel based on their acoustic-frequency responses measured at 18, 38, 120, and 200 kHz. At two fishing grounds during the 2008 survey, 332 schools were identified as sandeel, based on the characteristics of the acoustic signal, and validated by trawl samples. The schools consisted almost entirely of 1-year-old sandeels on one of the grounds, and 2-year-olds on the other. In this study, the potential of acoustic-frequency responses is advanced to classify the sizes of fish in them. A discriminant analysis using frequency responses as independent variables was able to differentiate between sandeel schools comprising 1- and 2-year-old fish (p < 0.001). Approximately 83% of the 2-year-old fish and 77% of the 1-year-old fish were classified correctly. The frequency responses at 18 and 38 kHz were the most important independent variables. Sandeel landings in the North Sea are normally dominated by 1- and 2-year-old sandeels in the first half of the year. This study revealed that these two age classes could be identified acoustically; a finding that may be important for acoustic surveys of sandeels and for management of the commercial sandeel fishery.

Multifrequency backscattering properties of Atlantic herring (Clupea harengus) and Norway pout (Trisopterus esmarkii)

2007 ◽  
Vol 64 (2) ◽  
pp. 362-374 ◽  
Author(s):  
Sascha M.M. Fässler ◽  
Rita Santos ◽  
Norma García-Núñez ◽  
Paul G Fernandes
Keyword(s):  
North Sea ◽  
Empirical Data ◽  
Ambient Pressure ◽  
Clupea Harengus ◽  
Atlantic Herring ◽  
The North ◽  
Fish Flesh ◽  
Fishing Vessels ◽  
The North Sea ◽  
Acoustic Surveys

The multifrequency backscattering characteristics of echotraces of Atlantic herring (Clupea harengus) and Norway pout (Trisopterus esmarkii) are described. These fish cohabit similar areas of the North Sea in summer and echotraces of their schools are difficult to distinguish. Mean volume backscattering strengths at 18, 38, 120, and 200 kHz were taken from the International North Sea Herring Acoustic Surveys along with coincident pelagic trawl samples. The results indicate that echotraces of these fish species cannot be distinguished on the basis of differences in backscattering at discrete frequencies typically used in fish surveys and on fishing vessels. However, some discrimination between herring size-classes was evident. The empirical data for herring were then compared with a backscattering model for herring combining fish flesh, the swimbladder, and the effect of increased pressure at depth. Both the empirical data and model data indicate that, compared with large herring, progressively smaller herring generally have higher backscattering at the lowest frequency (18 kHz), although variability was high. According to the model, this frequency-specific signature is due to the progressively more significant contribution made by the fish body compared with the swimbladder, as the latter diminishes owing to an increase in ambient pressure in deeper water.

scholarly journals Impacts of the local environment on recruitment: a comparative study of North Sea and Baltic Sea fish stocks

2014 ◽  
Vol 72 (5) ◽  
pp. 1323-1335 ◽  
Author(s):  
Laurène Pécuchet ◽  
J. Rasmus Nielsen ◽  
Asbjørn Christensen
Keyword(s):  
Baltic Sea ◽  
North Sea ◽  
Environmental Variables ◽  
Local Environment ◽  
Water Current ◽  
The Baltic Sea ◽  
Fish Stocks ◽  
The North ◽  
The North Sea ◽  
The Baltic

Abstract While the impact of environmental forcing on recruitment variability in marine populations remains largely elusive, studies spanning large spatial areas and many stocks are able to identify patterns common to different regions and species. In this study, we investigate the effects of the environment on the residuals of a Ricker stock–recruitment (SR) model, used as a proxy of prerecruits' survival, of 18 assessed stocks in the Baltic and North Seas. A probabilistic principal components (PCs) analysis permits the identification of groups of stocks with shared variability in the prerecruits' survival, most notably a group of pelagics in the Baltic Sea and a group composed of gadoids and herring in the North Sea. The first two PCs generally grouped the stocks according to their localizations: the North Sea, the Kattegat–Western Baltic, and the Baltic Sea. This suggests the importance of the local environmental variability on the recruitment strength. Hence, the prerecruits' survival variability is studied according to geographically disaggregated and potentially impacting abiotic or biotic variables. Time series (1990–2009) of nine environmental variables consistent with the spawning locations and season for each stock were extracted from a physical–biogeochemical model to evaluate their ability to explain the survival of prerecruits. Environmental variables explained &gt;70% of the survival variability for eight stocks. The variables water current, salinity, temperature, and biomass of other fish stocks are regularly significant in the models. This study shows the importance of the local environment on the dynamics of SR. The results provide evidence of the necessity of including environmental variables in stock assessment for a realistic and efficient management of fisheries.

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