A coupled stock-recruitment-age-structured model of the North Sea cod under the influence of depensation

2013 ◽  
Vol 253 ◽  
pp. 1-8 ◽  
Author(s):  
Reniel B. Cabral ◽  
Porfirio M. Aliño ◽  
May T. Lim
Keyword(s):  
North Sea ◽  
Structured Model ◽  
The North ◽  
Stock Recruitment ◽  
The North Sea ◽  
Age Structured ◽  
Age Structured Model

STABILITY ANALYSIS OF A CONTINUOUS AGE-STRUCTURED MODEL WITH SPECIFIC REFERENCE TO NORTH SEA COD

2004 ◽  
Vol 12 (03) ◽  
pp. 249-260
Author(s):  
J. M. ANDREWS ◽  
S. P. BLYTHE ◽  
W. S. C. GURNEY
Keyword(s):  
Life History ◽  
Stability Analysis ◽  
North Sea ◽  
Specific Reference ◽  
Structured Model ◽  
The North ◽  
The North Sea ◽  
Age Structured ◽  
The Stability ◽  
Age Structured Model

We examine the stability of a class of continuous age-structured models. Stability borders are established for the different parameters in the model, including levels required for viability. Two examples are then given, the first is a simple model for which the analysis is straightforward. An example is then shown of the cod population in the North Sea, which involves more complicated life history structures making stability analysis more difficult. The model predicts that the North Sea population will go extinct if fishing levels remain high. We show, however, that if mortality was lowered it would eventually be possible for the population to reach a point where it was stable and within safe biological limits.

scholarly journals A decline in primary production in the North Sea over 25 years, associated with reductions in zooplankton abundance and fish stock recruitment

2017 ◽  
Vol 24 (1) ◽  
pp. e352-e364 ◽  
Author(s):  
Elisa Capuzzo ◽  
Christopher P. Lynam ◽  
Jon Barry ◽  
David Stephens ◽  
Rodney M. Forster ◽  
...  
Keyword(s):  
Primary Production ◽  
North Sea ◽  
Fish Stock ◽  
Zooplankton Abundance ◽  
The North ◽  
Stock Recruitment ◽  
The North Sea

Equilibrium Yields and Yield Isopleths from a General Age-Structured Model of Harvested Populations

1985 ◽  
Vol 42 (11) ◽  
pp. 1766-1771 ◽  
Author(s):  
Timothy A. Lawson ◽  
Ray Hilborn
Keyword(s):  
Structured Model ◽  
Surplus Production ◽  
Pacific Halibut ◽  
Production Models ◽  
The Pacific ◽  
Hippoglossus Stenolepis ◽  
Equilibrium Yield ◽  
Stock Recruitment ◽  
Age Structured ◽  
Age Structured Model

The equilibrium properties of an age-structured model that includes any arbitrary age-specific weights, vulnerabilities, fecundities, and natural mortality rates, combined with stock–recruitment relationships, are derived. The numbers, biomass, and catch at each age can be calculated quite simply. These relationships can be used to construct yield-isopleth diagrams, or to plot equilibrium yield and biomass against harvest intensity. We used the results to compute yield isopleths for the Pacific halibut (Hippoglossus stenolepis) fishery. The analysis can also include a fishing season of any specified length. Relationships are given to translate the aggregate properties of the age-structured models into several alternative surplus production models.

scholarly journals The implications of warming climate for the management of North Sea demersal fisheries

2005 ◽  
Vol 62 (7) ◽  
pp. 1322-1326 ◽  
Author(s):  
R.M. Cook ◽  
M.R. Heath
Keyword(s):  
North Sea ◽  
Reference Points ◽  
The North ◽  
Stock Biomass ◽  
Spawning Stock ◽  
Stock Recruitment ◽  
The North Sea ◽  
State Of The Environment ◽  
Negative Relationships ◽  
Positive Effect

Abstract Since the 1950s, records from the North Sea show a gradual increase in temperature. Using temperature as a proxy indexing the state of the environment, relationships between recruitment, spawning-stock biomass, and temperature are investigated for major North Sea stocks. Cod, plaice, and sole exhibit significant negative relationships between temperature and recruitment, while there is evidence of a positive effect for saithe and whiting. Stock-recruitment models that incorporate temperature are developed and used to examine implications for the management of these stocks with small increases in mean winter sea surface temperature. These suggest that for cod, minimum safe biomass reference points are unlikely to be achieved even at fishing mortality rates that are considered safe. The same analysis suggests that sustainable fishing for cod is still possible with higher yields than have been experienced in recent years.

scholarly journals Integrating stochastic age-structured population dynamics into complex fisheries economic models for management evaluations: the North Sea saithe fishery as a case study

2014 ◽  
Vol 71 (7) ◽  
pp. 1638-1652 ◽  
Author(s):  
Sarah Laura Simons ◽  
Heleen Bartelings ◽  
Katell Gaelle Hamon ◽  
Alexander Johannes Kempf ◽  
Ralf Döring ◽  
...  
Keyword(s):  
Population Dynamics ◽  
North Sea ◽  
The North ◽  
Control Rules ◽  
Structured Population ◽  
Structured Population Dynamics ◽  
The North Sea ◽  
Age Structured ◽  
Age Structured Population ◽  
Harvest Control Rules

There is growing interest in bioeconomic models as tools for understanding pathways of fishery behaviour in order to assess the impact of alternative policies on natural resources. A model system is presented that combines stochastic age-structured population dynamics with complex fisheries economics. Explicitly, the economic response of fleet segments to changes in stock development is analysed by applying observed values and stochastic recruitment. The optimization of net profits determines the fishing effort and the investment and disinvestment behaviour of fleet segments, which, in turn, affect the level of catch rates and discards. This tool was applied to the North Sea saithe fishery, where ICES re-evaluated the existing EU–Norway management plan, focusing on biological reference points only. Two scenarios were tested with alternative harvest control rules and then contrasted with one unregulated scenario with no quotas and driven by optimizing the net profit of the whole fleet. The model showed the success of both harvest control rules in rebuilding the stock and the associated costs to the fleets in terms of maximal 21% reduction in net profits, 21% reduction in crew wages and 11% reduction in fleet size in the midterm (2007–2015). In the long term (2022), successful stock recovery coincided with net profits almost equalling that of the unrestricted fishery. The model is highly sensitive to the parameter values but can be used strategically, providing a qualitative understanding of the anticipated relative changes.

An Analysis of the Hecate Strait Pacific Cod Fishery Using an Age-structured Model Incorporating Density-dependent Effects

1983 ◽  
Vol 40 (8) ◽  
pp. 1233-1243 ◽  
Author(s):  
D. A. Fournier
Keyword(s):  
Fishing Effort ◽  
Natural Mortality ◽  
Pacific Cod ◽  
Structured Model ◽  
Density Dependent ◽  
Gadus Macrocephalus ◽  
Stock Recruitment ◽  
Age Structured ◽  
Age Structured Model ◽  
Relationship Of

An age-structured model was used to analyze the Hecate Strait Pacific cod (Gadus macrocephalus) fishery for the years 1960–80. The data consisted of estimates of fishing effort, together with estimates of numbers of fish at age caught in each year. The latter estimates were derived from length–frequency analysis. A stock–recruitment relationship of the Ricker type with an additional environmental factor was estimated. The data is also analyzed for evidence of the existence of age-dependent trends in natural mortality, density-dependent trends in natural mortality and catchability, and for time-dependent trends in catchability. Evidence of a density-dependent trend in natural mortality was discovered. The average level of natural mortality was also estimated to be 0.65.

An age-structured model with leading management parameters, incorporating age-specific selectivity and maturity

2008 ◽  
Vol 65 (2) ◽  
pp. 286-296 ◽  
Author(s):  
Robyn E Forrest ◽  
Steven J.D. Martell ◽  
Michael C Melnychuk ◽  
Carl J Walters
Keyword(s):  
Life History Traits ◽  
Stock Assessment ◽  
Maximum Sustainable Yield ◽  
Reference Points ◽  
Fish Stock ◽  
Structured Model ◽  
Specific Selectivity ◽  
Stock Recruitment ◽  
Age Structured ◽  
Age Structured Model

Previous authors have shown analytically that the optimal equilibrium harvest rate (UMSY) for an iteroparous fish stock is a function of the slope of the stock-recruitment curve at low stock size (α) and that UMSY can therefore be considered a direct measure of stock productivity. As such, it can be used as a leading parameter in stock assessment models and directly estimated using Bayesian or similar techniques. Here we present an alternative method for deriving α from UMSY that incorporates age-specific selectivity and fecundity, avoiding assumptions of knife-edged recruitment and maturity. We present an age-structured model with two fisheries reference points (UMSY and maximum sustainable yield, MSY) as its leading parameters. We show equilibrium properties of the model, chiefly in terms of its ability to show relationships between life history traits, density dependence, and UMSY. We also demonstrate a simple Bayesian estimation routine to illustrate estimation of UMSY and MSY directly from data. We compare our results to those from a structurally identical model with leading biological parameters. Using models with leading management parameters can improve communicability of results to managers.

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