Schools and clusters: Interannual variability in the aggregative behavior of North Sea herring from acoustic surveys

1999 ◽  
Vol 105 (2) ◽  
pp. 996-996
Author(s):  
Richard Aukland ◽  
David Reid
Keyword(s):  
Interannual Variability ◽  
North Sea ◽  
Aggregative Behavior ◽  
Acoustic Surveys

scholarly journals Thermohaline forcing and interannual variability of northwestern inflows into the northern North Sea

2017 ◽  
Vol 138 ◽  
pp. 120-131 ◽  
Author(s):  
Peter M.F. Sheehan ◽  
Barbara Berx ◽  
Alejandro Gallego ◽  
Rob A. Hall ◽  
Karen J. Heywood ◽  
...  
Keyword(s):  
Interannual Variability ◽  
North Sea ◽  
Northern North Sea

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.

Modeling the effects of fish migration on bias and variance in area-swept estimates of biomass: a vector-based approach

1998 ◽  
Vol 55 (12) ◽  
pp. 2622-2641 ◽  
Author(s):  
Murdoch K McAllister
Keyword(s):  
Interannual Variability ◽  
Fish Abundance ◽  
Fish Migration ◽  
Fish Biomass ◽  
Trawl Survey ◽  
Migration Rates ◽  
Acoustic Surveys ◽  
Survey Designs ◽  
Migration Velocities

Estimates of fish abundance from trawl and acoustic surveys are typically imprecise and may often be biased because of uncontrollable factors such as fish migration. In this paper, I present a model for the bias in area-swept biomass estimates when fish migration occurs as the survey is conducted. Bias in acoustic and trawl survey biomass estimates is treated as a function of the direction and speed of the vessel and the fish in each survey transect and results mainly from distortions in the observed area across fish aggregations. I use the model to evaluate the magnitude and direction of bias and interannual variability in biomass estimates from fish migration in systematic transect survey designs. For even relatively low fish migration velocities (<0.5 m/s), bias in estimated fish biomass can be very large (>500%). Furthermore, relatively small interannual variability in fish migration rates and vessel speeds (e.g., CV = 0.1 for each) can result in very large interannual error variability in biomass estimates (e.g., CV > 0.5). Designs with the least bias and variance in biomass estimates had the fastest vessel speeds along transects, more survey vessels, shorter transects, and transects aligned roughly parallel to the direction of fish migration.

Interannual variability of sorted bedforms in the coastal German Bight (SE North Sea)

2015 ◽  
Vol 111 ◽  
pp. 31-41 ◽  
Author(s):  
F. Mielck ◽  
P. Holler ◽  
D. Bürk ◽  
H.C. Hass
Keyword(s):  
Interannual Variability ◽  
North Sea ◽  
German Bight
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