scholarly journals Do North Sea cod (Gadus morhua) fisheries maintain high catch rates at low stock size?

2008 ◽  
Vol 65 (9) ◽  
pp. 1800-1813 ◽  
Author(s):  
Anna Rindorf ◽  
Bo Sølgaard Andersen
Keyword(s):  
Spatial Distribution ◽  
North Sea ◽  
Gadus Morhua ◽  
Commercial Fishing ◽  
Stock Size ◽  
Two Factors ◽  
Cod Fisheries ◽  
Catch Rates ◽  
Fishing Fleets ◽  
The Relationship

This study presents an investigation of the relationship between stock size of North Sea cod ( Gadus morhua ) and catch rates in seven commercial fishing fleets. The shape of the relationship was estimated using a new model allowing both density-dependent changes in catchability and bias in the assessment biomass estimates. Catchability in fisheries targeting a mixed species composition either remained constant or decreased with decreasing stock size, whereas catchability in targeted cod fisheries increased with decreasing stock size. However, even in the cases where catchability increased, the change was insufficient to compensate for the decrease in stock size, and catch rates of all fleets decreased. Two factors that could lead to nonconstant catchability were investigated: (i) the presence of a decoupling between stock size and density in high-density areas and (ii) the presence of concurrent shifts in the spatial distribution of the cod stock and the cod fishery. No evidence of the former was found, but there was a northern shift in the spatial distribution of both effort and the cod stock.

Effect of bottom type on catch rates of North Sea cod (Gadus morhua) in surveys with commercial fishing vessels

2009 ◽  
Vol 96 (2-3) ◽  
pp. 244-251 ◽  
Author(s):  
Kai Wieland ◽  
Eva Maria Fenger Pedersen ◽  
Hans J. Olesen ◽  
Jan E. Beyer
Keyword(s):  
North Sea ◽  
Gadus Morhua ◽  
Commercial Fishing ◽  
Bottom Type ◽  
Fishing Vessels ◽  
Catch Rates

Partial Recruitment Considerations in Setting Catch Quotas

1993 ◽  
Vol 50 (4) ◽  
pp. 734-742 ◽  
Author(s):  
A. F. Sinclair
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Age Groups ◽  
Combined Effects ◽  
Total Allowable Catch ◽  
Catch Rates ◽  
Fishing Fleets ◽  
The Individual ◽  
Nova Scotian ◽  
Target Fishing

An approach is presented for investigating the interactions between fishing fleets that compete by exploiting different age-groups of the same resource population. The term "partial recruitment" (PR) is used to describe the age-specific exploitation pattern experienced by a population, either from individual fishing fleets or the combined effects of several fleets. Methods are presented to calculate catch quotas for the individual fleets if the management objective is to keep fleet effort constant, or alternatively to predict catch rates by fleet if the allocation rules are based on a percentage sharing of the total allowable catch (TAC) among fleets. Simulations based on an Atlantic cod (Gadus morhua) fishery on the Nova Scotian Shelf is used to illustrate the method. The results indicate the importance of considering differences in PR among competing fishing fleets when setting catch quotas. The relative effort exerted by the fleets will affect target fishing mortalities. The fleet that concentrates on younger fish can intercept recruitment. Since the fleets exploit different age-groups, changes in fishable biomass due to recruitment variation are lagged, and fishing success will vary among fleets. Understanding the dynamics of PR may help explain why certain fleets either exceed or fall short of catch quotas.

The spatial distribution of cod (Gadus morhua L.) spawning grounds in the Kattegat, eastern North Sea

2008 ◽  
Vol 90 (1-3) ◽  
pp. 36-44 ◽  
Author(s):  
F. Vitale ◽  
P. Börjesson ◽  
H. Svedäng ◽  
M. Casini
Keyword(s):  
Spatial Distribution ◽  
North Sea ◽  
Gadus Morhua ◽  
Spawning Grounds

scholarly journals Growth, temperature, and density relationships of North Sea cod (Gadus morhua)

2008 ◽  
Vol 65 (3) ◽  
pp. 456-470 ◽  
Author(s):  
Anna Rindorf ◽  
Henrik Jensen ◽  
Corinna Schrum
Keyword(s):  
Ambient Temperature ◽  
North Sea ◽  
Growth Temperature ◽  
Gadus Morhua ◽  
Demersal Fish ◽  
Fish Biomass ◽  
Fishing Mortality ◽  
Prey Fish ◽  
Fish Prey ◽  
The Relationship

This study presents an analysis of the relationship between ambient temperature, cod density, fishing mortality, prey fish biomass, and growth of North Sea cod (Gadus morhua) as estimated from survey catches during the period from 1983 to 2006. Growth of young cod was positively related to temperature; however, although temperature increased, distribution of 1-year-olds changed concurrently and no increase in length at age 1 occurred. Growth from age 1 to age 2 decreased as ambient biomass of sandeel and density of cod decreased, whereas growth of cod older than 2 years decreased with increasing density of cod and increased with increasing biomass of demersal fish prey. Though growth of juveniles was strongly positively correlated to ambient temperature, no indication of direct temperature limitation of growth of older North Sea cod was found.

Development of integrated habitat indices for bigeye tuna, Thunnus obesus, in waters near Palau

2012 ◽  
Vol 63 (12) ◽  
pp. 1244 ◽  
Author(s):  
Yuwei Li ◽  
Liming Song ◽  
Tom Nishida ◽  
Panfeng Gao
Keyword(s):  
Spatial Distribution ◽  
Dissolved Oxygen ◽  
Environmental Variables ◽  
Weighted Average ◽  
Catch Per Unit Effort ◽  
Average Temperature ◽  
Pelagic Fishes ◽  
Thunnus Obesus ◽  
Catch Rates ◽  
The Relationship

A survey was conducted in waters near Palau in 2005, to improve our understanding of the relationship between environmental variables and the spatial distributions of Thunnus obesus. Catch rates and environmental variables (water temperature, salinity and dissolved oxygen) at six depth strata between 40 and 280 m were collected at 77 sampling stations in the survey. Models were developed to estimate an integrated habitat index (IHI) for T. obesus on the basis of quantile regression. The findings of the present study were as follows: (1) the performance of IHI models in predicting habitat utilisation by T. obesus was good, (2) the impacts of the weighted average temperature and dissolved oxygen were significant on the spatial distribution of T. obesus, (3) the influence of the environmental variables on T. obesus distribution differed among different depth strata, (4) the present study provides an effective approach to predict the spatial distribution of the pelagic fishes caught by longline and (5) the weighted average temperature and dissolved oxygen should be included in the T. obesus catch per unit effort (CPUE) standardisations.

scholarly journals Abundance and spatial distribution of brown crab (Cancer pagurus) from fishery-independent dredge and trawl surveys in the North Sea

2020 ◽  
Author(s):  
Carlos Mesquita ◽  
Helen Dobby ◽  
Graham J Pierce ◽  
Catherine S Jones ◽  
Paul G Fernandes
Keyword(s):  
Spatial Distribution ◽  
North Sea ◽  
Stock Assessment ◽  
Additive Models ◽  
Early Years ◽  
The North ◽  
Cancer Pagurus ◽  
The North Sea ◽  
Catch Rates ◽  
Trawl Surveys

Abstract Brown crab (Cancer pagurus) is a widely distributed crustacean that occurs around the British coastline supporting important commercial fisheries. The habitat preferences of brown crab around Scotland are poorly documented and for the purposes of stock assessment, the species is considered data-poor. Based on an analysis of dredge and trawl surveys taking place in the North Sea (2008–2018), we describe the spatial distribution of brown crab and for the first time, develop abundance and recruitment indices for the species. We make use of geostatistical methods and apply generalized additive models to model catch rates in relation to a number of explanatory variables (depth, distance to the coast, sediment type and year). The dredge and trawl abundance indices were correlated showing a similar trend of increasing catch rates in the early years of the time series up to 2016 and a subsequent reduction. The recruitment index showed a gradual increase in captured juvenile crabs up to 2014 followed by a steep decrease with 2018 being the lowest value estimated. The derivation of robust indicators of stock abundance will contribute to the stock assessment of this species and enable the provision of improved fisheries management advice for brown crab around Scotland.

scholarly journals Estimating the relationship between abundance and distribution

2012 ◽  
Vol 69 (2) ◽  
pp. 382-397 ◽  
Author(s):  
Anna Rindorf ◽  
Peter Lewy
Keyword(s):  
Spatial Distribution ◽  
Count Data ◽  
Gini Index ◽  
Euclidean Distance ◽  
Gadus Morhua ◽  
Lorenz Curves ◽  
Centre Of Gravity ◽  
Unbiased Estimates ◽  
Abundance And Distribution ◽  
The Relationship

Numerous studies investigate the relationship between abundance and distribution using indices reflecting one of the three aspects of distribution: proportion of area occupied, aggregation, and geographical range. Using simulations and analytical derivations, we examine whether these indices provide unbiased estimates of the relationship when estimated from count data. The indices investigated include the proportion of empty samples, the proportion of structurally empty samples, Lloyds index of patchiness, measures derived from Lorenz curves (such as D95 and the Gini index), and measures based on Euclidean distance to the centre of gravity of the spatial distribution. Only the proportion of structurally empty areas, Lloyds index, and indices of the distance to the centre of gravity of the spatial distribution are unbiased at all levels of abundance. The remaining indices generate relationships between abundance and distribution even in cases where no underlying relationships exists, although the problem decreases for measures derived from Lorenz curves when samples contain more than four individuals on average. To illustrate the problem, the indices are applied to juvenile North Sea cod, Gadus morhua .

scholarly journals Insights Into the Correspondence Between Land Use Pattern and Spatial Distribution of Rail Transit Services

2021 ◽  
Author(s):  
Zhongqi Wang ◽  
Qi Han ◽  
Bauke de Vries ◽  
Li Dai
Keyword(s):  
Land Use ◽  
Spatial Distribution ◽  
Operations Management ◽  
Latent Variable ◽  
Structural Equation ◽  
Equation Modeling ◽  
Rail Transit ◽  
Land Use Patterns ◽  
Transit Services ◽  
The Relationship

AbstractThe identification of the relationship between land use and transport lays the foundation for integrated land use and transport planning and management. This work aims to investigate how rail transit is linked to land use. The research on the relationship between land use and rail-based transport is dominated by the impacts of rail projects on land use, without an in-depth understanding of the reverse. However, it is important to note that issues of operation management rather than new constructions deserve greater attention for regions with established rail networks. Given that there is a correspondence between land use patterns and spatial distribution of heavy railway transit (HRT) services at such regions, the study area (i.e., the Netherlands) is partitioned by the Voronoi diagram of HRT stations and the causal relationship between land use and HRT services is examined by structural equation modeling (SEM). The case study of Helmond (a Dutch city) shows the potential of the SEM model for discussing the rail station selection problem in a multiple transit station region (MTSR). Furthermore, in this study, the node place model is adapted with the derivatives of the SEM model (i.e., the latent variable scores for rail service levels and land use characteristics), which are assigned as node and place indexes respectively, to analyze and differentiate the integration of land use and HRT services at the regional level. The answer to whether and how land use affects rail transit services from this study strengthens the scientific basis for rail transit operations management. The SEM model and the modified node place model are complementary to be used as analytical and decision-making tools for rail transit-oriented regional development.

scholarly journals Double parton distributions in the pion from lattice QCD

2021 ◽  
Vol 2021 (2) ◽  
Author(s):  
Gunnar S. Bali ◽  
Luca Castagnini ◽  
Markus Diehl ◽  
Jonathan R. Gaunt ◽  
Benjamin Gläßle ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Lattice Qcd ◽  
Quark Mass ◽  
Matrix Elements ◽  
Parton Distributions ◽  
Almost All ◽  
The Relationship

Abstract We perform a lattice study of double parton distributions in the pion, using the relationship between their Mellin moments and pion matrix elements of two local currents. A good statistical signal is obtained for almost all relevant Wick contractions. We investigate correlations in the spatial distribution of two partons in the pion, as well as correlations involving the parton polarisation. The patterns we observe depend significantly on the quark mass. We investigate the assumption that double parton distributions approximately factorise into a convolution of single parton distributions.

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