scholarly journals Weighting of acoustic- and trawl-survey indices for the assessment of North Sea herring

2003 ◽  
Vol 60 (3) ◽  
pp. 463-471 ◽  
Author(s):  
E.J Simmonds
Keyword(s):  
North Sea ◽  
Assessment Model ◽  
The Other ◽  
Trawl Survey ◽  
Acoustic Survey ◽  
Weighting Method ◽  
The North ◽  
The North Sea ◽  
Using Data ◽  
Almost All

Abstract Acoustic surveys are used in 20 stock assessments within the ICES community, and almost all as relative indices of abundance, but little has been done to explore their performance in detail. The North Sea herring acoustic survey started in 1979 and by 1984 had become an internationally-coordinated survey conducted annually in July. Along with trawl- and larvae-survey indices, it has been used to tune a catch-at-age assessment model of North Sea herring. In this article, the precision of the survey is estimated, using data at ICES statistical-rectangle level from 1989 to 2001, and bootstrap-resampling methods modified by geostatistical estimates of the spatial autocorrelation. Similar techniques are applied to the larvae, Methot and trawl surveys that provide the other data on the distribution and abundance of North Sea herring. The comparison of survey performance is also examined using the bootstrap estimates of abundance to give 1000 simulated assessments of North Sea herring using the integrated catch-at-age (ICA) method. The results of these analyses are compared and the annual acoustic survey is shown to provide the most precise estimate of relative abundance for adult North Sea herring each year. The weighting of the various indices within the assessment is investigated. A weighting method is presented that provides a more precise method for estimating the stock. The more precise assessments are compared for retrospective pattern. An assessment is proposed which provides the most precise stock estimates with the best retrospective pattern. This assessment has been reviewed and accepted by the ICES Advisory Committee on Fisheries Management. The importance of the acoustic survey and its contribution to the assessment in relation to the other indices is discussed.

scholarly journals Estimating year-class strength of Icelandic summer-spawning herring on the basis of two survey methods

2007 ◽  
Vol 64 (6) ◽  
pp. 1182-1190 ◽  
Author(s):  
Asta Gudmundsdottir ◽  
Gudmundur J. Oskarsson ◽  
Sveinn Sveinbjörnsson
Keyword(s):  
Survey Methods ◽  
Assessment Model ◽  
The Other ◽  
Trawl Survey ◽  
Acoustic Survey ◽  
Nursery Areas ◽  
Shrimp Trawl ◽  
Class Strength ◽  
Using Data ◽  
Better Than

Abstract Gudmundsdottir, A., Oskarsson, G. J., and Sveinbjörnsson, S. 2007. Estimating year-class strength of Icelandic summer-spawning herring on the basis of two survey methods. – ICES Journal of Marine Science, 64: 1182–1190. Recruitment indices at age 1 and 2 were constructed for Icelandic summer-spawning herring using data from two inherently different survey methods on their nursery areas for the years 1988–2003. The surveys were a shrimp, bottom-trawl survey and a herring acoustic survey. Indices were compared with the year-class strength at age 2 derived from an assessment model (AMCI) used for the stock. A juvenile index at age 1 from the acoustic survey and at age 2 from the shrimp-trawl survey correlated significantly with the modelled recruitment, although only marginally with each other. One index was not considered markedly better than the other, and both have shortcomings even if the acoustic survey is believed better than the trawl survey for quantifying juvenile herring. The recruitment index at age 1 derived from the acoustic survey can be improved as an indicator of recruitment if that survey were to be extended to cover the nursery areas off western and southeastern Iceland, and the same areas covered each year.

scholarly journals Spatial interactions between saithe (Pollachius virens) and hake (Merluccius merluccius) in the North Sea

2014 ◽  
Vol 71 (6) ◽  
pp. 1342-1355 ◽  
Author(s):  
Xochitl Cormon ◽  
Christophe Loots ◽  
Sandrine Vaz ◽  
Youen Vermard ◽  
Paul Marchal
Keyword(s):  
North Sea ◽  
Linear Models ◽  
Spatial Dynamics ◽  
Distribution Patterns ◽  
Trawl Survey ◽  
Spatial Interactions ◽  
Merluccius Merluccius ◽  
The North ◽  
Sediment Types ◽  
The North Sea

Spatial interactions between saithe (Pollachius virens) and hake (Merluccius merluccius) were investigated in the North Sea. Saithe is a well-established species in the North Sea, while occurrence of the less common hake has recently increased in the area. Spatial dynamics of these two species and their potential spatial interactions were explored using binomial generalized linear models (GLM) applied to the International Bottom Trawl Survey (IBTS) data from 1991 to 2012. Models included different types of variables: (i) abiotic variables including sediment types, temperature, and bathymetry; (ii) biotic variables including potential competitors and potential preys presence; and (iii) spatial variables. The models were reduced and used to predict and map probable habitats of saithe, hake but also, for the first time in the North Sea, the distribution of the spatial overlap between these two species. Changes in distribution patterns of these two species and of their overlap were also investigated by comparing species’ presence and overlap probabilities predicted over an early (1991–1996) and a late period (2007–2012). The results show an increase in the probability over time of the overlap between saithe and hake along with an expansion towards the southwest and Scottish waters. These shifts follow trends observed in temperature data and might be indirectly induced by climate changes. Saithe, hake, and their overlap are positively influenced by potential preys and/or competitors, which confirms spatial co-occurrence of the species concerned and leads to the questions of predator–prey relationships and competition. Finally, the present study provides robust predictions concerning the spatial distribution of saithe, hake, and of their overlap in the North Sea, which may be of interest for fishery managers.

scholarly journals Opportunistically recorded acoustic data support Northeast Atlantic mackerel expansion theory

2015 ◽  
Vol 73 (4) ◽  
pp. 1115-1126 ◽  
Author(s):  
Jeroen van der Kooij ◽  
Sascha M.M. Fässler ◽  
David Stephens ◽  
Lisa Readdy ◽  
Beth E. Scott ◽  
...  
Keyword(s):  
North Sea ◽  
Stock Assessment ◽  
Detection Algorithm ◽  
Trawl Survey ◽  
Northeast Atlantic ◽  
Acoustic Data ◽  
The North ◽  
The North Sea ◽  
Northern North Sea ◽  
Feeding Grounds

Abstract Fisheries independent monitoring of widely distributed pelagic fish species which conduct large seasonal migrations is logistically complex and expensive. One of the commercially most important examples of such a species in the Northeast Atlantic Ocean is mackerel for which up to recently only an international triennial egg survey contributed to the stock assessment. In this study, we explore whether fisheries acoustic data, recorded opportunistically during the English component of the North Sea International Bottom Trawl Survey, can contribute to an improved understanding of mackerel distribution and provide supplementary data to existing dedicated monitoring surveys. Using a previously published multifrequency acoustic mackerel detection algorithm, we extracted the distribution and abundance of schooling mackerel for the whole of the North Sea during August and September between 2007 and 2013. The spatio-temporal coverage of this unique dataset is of particular interest because it includes part of the unsurveyed summer mackerel feeding grounds in the northern North Sea. Recent increases in landings in Icelandic waters during this season suggested that changes have occurred in the mackerel feeding distribution. Thus far it is poorly understood whether these changes are due to a shift, i.e. mackerel moving away from their traditional feeding grounds in the northern North Sea and southern Norwegian Sea, or whether the species' distribution has expanded. We therefore explored whether acoustically derived biomass of schooling mackerel declined in the northern North Sea during the study period, which would suggest a shift in mackerel distribution rather than an expansion. The results of this study show that in the North Sea, schooling mackerel abundance has increased and that its distribution in this area has not changed over this period. Both of these findings provide, to our knowledge, the first evidence in support of the hypothesis that mackerel have expanded their distribution rather than moved away.

Spatial and temporal dynamics of European hake (Merluccius merluccius) in the North Sea

2018 ◽  
Vol 75 (6) ◽  
pp. 2033-2044 ◽  
Author(s):  
Arved Staby ◽  
Jon Egil Skjæraasen ◽  
Audrey J Geffen ◽  
Daniel Howell
Keyword(s):  
North Sea ◽  
Temporal Dynamics ◽  
Trawl Survey ◽  
Merluccius Merluccius ◽  
Frequency Distributions ◽  
The North ◽  
The North Sea ◽  
Northern North Sea ◽  
Central North Sea ◽  
European Hake

Abstract Catches of European hake (Merluccius merluccius) in the North Sea have increased substantially during the last decade, even though there is no directed commercial fishery of hake in this area. We analysed the spatial distributions of hake in the northern the parts of its range, (where it is less well-studied), using ICES international bottom trawl survey data from 1997 to 2015. We examine length-frequency distributions for (i) distinct modes enabling the assignment of fish into categories which likely corresponded to the ages 1, 2, and 3+ and (ii) patterns of seasonal spatial distribution for the different groups. Age categories 1 and 2 fish were most abundant in the northern North Sea, and appear to remain in the North Sea until 2 years of age, when they move into deeper waters. Their distribution has expanded into the western-central North Sea in the last decade. Age category 3+ fish were most abundant in the northern and central North Sea during summer, indicating a seasonal influx of large individuals into this area likely associated with spawning activity. The distribution of these older fish has gradually expanded westward in both seasons.

scholarly journals Report on the Surface Collections made by Mr. W. T. Grenfell in the North Sea and West of Scotland

1890 ◽  
Vol 1 (4) ◽  
pp. 376-381 ◽  
Author(s):  
Gilbert C. Bourne
Keyword(s):  
Sulphuric Acid ◽  
North Sea ◽  
Deep Sea ◽  
Early Spring ◽  
The Other ◽  
The West ◽  
The North ◽  
The North Sea

Mr. Wilfrid Grenfell, the Superintendent of the Mission to Deep Sea Fishermen, has most kindly arranged to carry on a series of observations on the pelagic fauna and the fishes of the seas traversed by the Mission boats in the course of their work. The following report gives an account of the pelagic fauna collected in the North Sea during the early spring, and in the west of Scotland and Kinsale Harbour during the summer. The collections were preserved in picro-sulphuric acid and spirit, and were forwarded to Plymouth for examination. Owing to pressure of work, and to my leaving Plymouth somewhat unexpectedly, I have not been able to make a thorough investigation of all the collections, but have worked out the Copepoda with care, and have confined myself to short notes on the other species.

scholarly journals Do Norway pout (Trisopterus esmarkii) die from spawning stress? Mortality of Norway pout in relation to growth, sexual maturity, and density in the North Sea, Skagerrak, and Kattegat

2012 ◽  
Vol 69 (2) ◽  
pp. 197-207 ◽  
Author(s):  
J. Rasmus Nielsen ◽  
Gwladys Lambert ◽  
Francois Bastardie ◽  
Henrik Sparholt ◽  
Morten Vinther
Keyword(s):  
North Sea ◽  
Sexual Maturity ◽  
Life History Traits ◽  
Trawl Survey ◽  
Older Individuals ◽  
Fishing Activity ◽  
The North ◽  
Spawning Areas ◽  
The North Sea ◽  
New Evidence

Abstract Nielsen, J. R., Lambert, G., Bastardie, F., Sparholt, H., and Vinther, M. 2012. Do Norway pout (Trisopterus esmarkii) die from spawning stress? Mortality of Norway pout in relation to growth, sexual maturity, and density in the North Sea, Skagerrak, and Kattegat. – ICES Journal of Marine Science, 69: 197–207. The mortality patterns of Norway pout (NP) are not well understood. It has been suggested that NP undergo heavy spawning mortality, and this paper summarizes and provides new evidence in support of this hypothesis. The very low–absent fishing activity in recent years provides a unique opportunity to analyse the natural life-history traits of cohorts in the NP stock in the North Sea. Based on the ICES trawl survey abundance indices, cohort mortality is found to significantly increase with age. We argue that this cannot be explained by selectiveness in the fishery, potential size-specific migrations out of the area, higher predation pressure on older individuals, or differences in survey catchability by NP age from before to after spawning and that it is higher in the main spawning areas than outside. We found that natural mortality (M) is significantly correlated with sexual maturity, sex, growth, and intraspecific stock density. All of this is consistent with a greater mortality occurring mainly from the first to the second quarter of the year, i.e. spawning mortality, which is discussed as being a major direct and indirect cause of stock mortality.

scholarly journals On the tides, bed and coasts of the North Sea or German Ocean

1854 ◽  
Vol 6 ◽  
pp. 201-202
Keyword(s):  
The Netherlands ◽  
North Sea ◽  
The Other ◽  
Great Similarity ◽  
Shetland Islands ◽  
Norwegian Coast ◽  
The North ◽  
The North Sea ◽  
The Baltic ◽  
Long Channel

The author commences his paper by remarking that great similarity of outline pervades the western shores of Ireland, Scotland and Norway, and then observes that the great Atlantic flood-tide wave, having traversed the shores of the former countries, strikes with great fury the Norwegian coast between the Lafoden Isles and Stadland, one portion proceeding to the north, while the other is deflected to the south, which last has scooped out along the coast, as far as the Sleeve at the mouth of the Baltic, a long channel from 100 to 200 fathoms in depth, almost close in shore, and varying from 50 to 100 miles in width. After describing his method of contouring and colouring the Admiralty chart of the North Sea, he traces the course of the tide-wave among the Orkney and Shetland Islands along the eastern shores of Scotland and England to the Straits of Dover, and along the western shores of Norway, Denmark and the Netherlands, to the same point.

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