scholarly journals Which are better, random or systematic acoustic surveys? A simulation using North Sea herring as an example

1996 ◽  
Vol 53 (1) ◽  
pp. 39-50 ◽  
Author(s):  
E Simmonds
Keyword(s):  
North Sea ◽  
Acoustic Surveys

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 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.

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