How to validate a length-based model of single-species fish stock dynamics

2006 ◽  
Vol 63 (11) ◽  
pp. 2531-2542 ◽  
Author(s):  
Kasper Kristensen ◽  
Peter Lewy ◽  
Jan E Beyer
Keyword(s):  
Survey Data ◽  
Gadus Morhua ◽  
Negative Binomial ◽  
Atlantic Cod ◽  
Population Level ◽  
Single Species ◽  
Model Complexity ◽  
Fish Stock ◽  
Statistical Hypotheses ◽  
The Baltic

This paper validates a new length-based model of the dynamics of fish stocks or crustaceans by hierarchically testing statistical hypotheses and thereby investigating model complexity. The approach is based entirely on scientific survey data and on determination of the statistical distributions of the number of fish caught per haul in each length class. In our example, the negative binomial distribution is statistically accepted and linked to the population level through the new length-based model. The model is derived from the characteristics of continuous recruitment, individually based growth, and continuous, length-dependent mortality rates. Continuous recruitment with annually varying recruitment peaks and individually based growth was crucial for obtaining a model that could be statistically accepted. Natural mortality was estimated as well by the model. The model was applied to survey data for Atlantic cod (Gadus morhua) in the Baltic. Its simple generic nature, as well as the validation procedure, is useful in studying and understanding life history and stock dynamics.

scholarly journals Implementing ecosystem-based fisheries management: from single-species to integrated ecosystem assessment and advice for Baltic Sea fish stocks

2013 ◽  
Vol 71 (5) ◽  
pp. 1187-1197 ◽  
Author(s):  
Christian Möllmann ◽  
Martin Lindegren ◽  
Thorsten Blenckner ◽  
Lena Bergström ◽  
Michele Casini ◽  
...  
Keyword(s):  
Baltic Sea ◽  
Fisheries Management ◽  
Gadus Morhua ◽  
Single Species ◽  
Clupea Harengus ◽  
Fish Stock ◽  
Fish Stocks ◽  
The Baltic ◽  
Ecosystem Based Fisheries Management ◽  
Sea Fish

Abstract Theory behind ecosystem-based management (EBM) and ecosystem-based fisheries management (EBFM) is now well developed. However, the implementation of EBFM exemplified by fisheries management in Europe is still largely based on single-species assessments and ignores the wider ecosystem context and impact. The reason for the lack or slow implementation of EBM and specifically EBFM is a lack of a coherent strategy. Such a strategy is offered by recently developed integrated ecosystem assessments (IEAs), a formal synthesis tool to quantitatively analyse information on relevant natural and socio-economic factors, in relation to specified management objectives. Here, we focus on implementing the IEA approach for Baltic Sea fish stocks. We combine both tactical and strategic management aspects into a single strategy that supports the present Baltic Sea fish stock advice, conducted by the International Council for the Exploration of the Sea (ICES). We first review the state of the art in the development of IEA within the current management framework. We then outline and discuss an approach that integrates fish stock advice and IEAs for the Baltic Sea. We intentionally focus on the central Baltic Sea and its three major fish stocks cod (Gadus morhua), herring (Clupea harengus), and sprat (Sprattus sprattus), but emphasize that our approach may be applied to other parts and stocks of the Baltic, as well as other ocean areas.

scholarly journals Non-linearity in stock–recruitment relationships of Atlantic cod: insights from a multi-model approach

2019 ◽  
Vol 77 (4) ◽  
pp. 1492-1502 ◽  
Author(s):  
Camilla Sguotti ◽  
Saskia A Otto ◽  
Xochitl Cormon ◽  
Karl M Werner ◽  
Ethan Deyle ◽  
...  
Keyword(s):  
Environmental Variables ◽  
Gadus Morhua ◽  
Fishery Management ◽  
Atlantic Cod ◽  
Stock Assessment ◽  
Fish Stock ◽  
Recovery Potential ◽  
Stock Recruitment ◽  
Model Approach ◽  
Non Parametric

Abstract The stock–recruitment relationship is the basis of any stock prediction and thus fundamental for fishery management. Traditional parametric stock–recruitment models often poorly fit empirical data, nevertheless they are still the rule in fish stock assessment procedures. We here apply a multi-model approach to predict recruitment of 20 Atlantic cod (Gadus morhua) stocks as a function of adult biomass and environmental variables. We compare the traditional Ricker model with two non-parametric approaches: (i) the stochastic cusp model from catastrophe theory and (ii) multivariate simplex projections, based on attractor state-space reconstruction. We show that the performance of each model is contingent on the historical dynamics of individual stocks, and that stocks which experienced abrupt and state-dependent dynamics are best modelled using non-parametric approaches. These dynamics are pervasive in Western stocks highlighting a geographical distinction between cod stocks, which have implications for their recovery potential. Furthermore, the addition of environmental variables always improved the models’ predictive power indicating that they should be considered in stock assessment and management routines. Using our multi-model approach, we demonstrate that we should be more flexible when modelling recruitment and tailor our approaches to the dynamical properties of each individual stock.

Survey gear calibration independent of spatial fish distribution

2004 ◽  
Vol 61 (4) ◽  
pp. 636-647 ◽  
Author(s):  
Peter Lewy ◽  
J Rasmus Nielsen ◽  
Holger Hovgård
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Survey Design ◽  
Fish Distribution ◽  
Simulation Studies ◽  
Conversion Factors ◽  
The Baltic ◽  
Standard Software ◽  
Track Line ◽  
Stock Abundance

Trawl surveys provide important information for evaluation of relative stock abundance fluctuations over time. Therefore, when survey gears or vessels are changed, it is important to compare the efficiency and selectivity of old and new gears and vessels. A method for estimation of conversion factors is developed based on a survey design where paired hauls are taken in the same trawl track line. The method explicitly accounts for changes in fish density caused by trawling disturbance. A generalized linear model for paired hauls catches is analytically derived and the gear conversion and disturbance parameters with their precision are obtained using standard software. Simulation studies carried out additionally showed that the estimated conversion factors were practically unbiased. Because of the independence of the spatial fish distribution, the new method is preferable to the traditional paired hauls design for which it is generally not possible to obtain the statistical properties of the estimated conversion factors. The paper is concluded with suggestions on how to optimize survey design. The method was used to estimate conversion factors for Atlantic cod (Gadus morhua) from Danish gear calibration experiments in the Baltic Sea.

scholarly journals Detecting regime shifts in fish stock dynamics

2015 ◽  
Vol 72 (11) ◽  
pp. 1619-1628 ◽  
Author(s):  
Tommi Perälä ◽  
Anna Kuparinen
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Stock Assessment ◽  
Detection Algorithm ◽  
Regime Shifts ◽  
Change Point Detection ◽  
Fish Stock ◽  
Fish Stocks ◽  
Data Generating Process ◽  
Change In Mean

Environmental factors such as water temperature, salinity, and the abundance of zooplankton can have major effects on certain fish stocks’ ability to produce juveniles and, thus, stock renewal ability. This variability in stock productivity manifests itself as different productivity regimes. Here, we detect productivity regime shifts by analyzing recruit-per-spawner time series with Bayesian online change point detection algorithm. The algorithm infers the time since the last regime shift (change in mean or variance or both) as well as the parameters of the data-generating process for the current regime sequentially. We demonstrate the algorithm’s performance using simulated recruitment data from an individual-based model and further apply the algorithm to stock assessment estimates for four Atlantic cod (Gadus morhua) stocks obtained from RAM legacy database. Our analysis shows that the algorithm performs well when the variability between the regimes is high enough compared with the variability within the regimes. The algorithm found several productivity regimes for all four cod stocks, and the findings suggest that the stocks are currently in low productivity regimes, which have started during the 1990s and 2000s.

scholarly journals Mitochondrial Cytochrome b DNA Sequence Variation of Atlantic Cod, Gadus Morhua, from the Baltic and the White Seas

Hereditas ◽  
2004 ◽  
Vol 129 (1) ◽  
pp. 37-43 ◽  
Author(s):  
Einar Árnason ◽  
Pétur Henry Petersen ◽  
Snaebjörn Pálsson
Keyword(s):  
Dna Sequence ◽  
Cytochrome B ◽  
Gadus Morhua ◽  
Sequence Variation ◽  
Atlantic Cod ◽  
Mitochondrial Cytochrome ◽  
Mitochondrial Cytochrome B ◽  
Dna Sequence Variation ◽  
The Baltic

scholarly journals Understanding the release efficiency of Atlantic cod (Gadus morhua) from trawls with a square mesh panel: effects of panel area, panel position, and stimulation of escape response

2014 ◽  
Vol 72 (2) ◽  
pp. 686-696 ◽  
Author(s):  
Bent Herrmann ◽  
Harald Wienbeck ◽  
Junita Diana Karlsen ◽  
Daniel Stepputtis ◽  
Erdmann Dahm ◽  
...  
Keyword(s):  
Escape Response ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Mesh Size ◽  
Accumulation Zone ◽  
Trawl Fishery ◽  
Trawl Fishing ◽  
Panel Effects ◽  
The Baltic ◽  
Stimulation Of

Abstract Based on size selectivity data for more than 25 000 cod (Gadus morhua) collected during experimental trawl fishing with six different codends, all of which included a square mesh panel, we investigated the effect on cod-release efficiency based on the size of the square mesh panel area, position of the square mesh panel, and stimulation of the escape response. Based on the results, we were able to explain why the BACOMA codend, applied in the Baltic Sea cod directed trawl fishery, releases juvenile cod efficiently, whereas other designs, including a square mesh panel with similar mesh size, are less efficient. Our main findings reveal that the release efficiency of the square mesh panel in the BACOMA codend depends largely on the overlap of the square mesh panel and the catch-accumulation zone in the codend, where cod do not have the option of just drifting further back in the trawl when proximate to the panel. On the contrary, the reduction in panel size by 50% did not significantly affect the release efficiency when the panel overlapped with the catch-accumulation zone. It was possible to stimulate an escape response for cod to achieve a release through a square mesh panel positioned away from the catch-accumulation zone. Our findings demonstrated that this release was as efficient as for a panel mounted in the catch-accumulation zone of the codend. Devices that stimulate behaviour may improve the release efficiency of cod through square mesh panels in other fisheries where this is a problem.

scholarly journals Relationships between fish stock changes in the Baltic Sea and the M74 syndrome, a reproductive disorder of Atlantic salmon (Salmo salar)

2011 ◽  
Vol 68 (10) ◽  
pp. 2134-2144 ◽  
Author(s):  
Jaakko Mikkonen ◽  
Marja Keinänen ◽  
Michele Casini ◽  
Jukka Pönni ◽  
Pekka J. Vuorinen
Keyword(s):  
Atlantic Salmon ◽  
Baltic Sea ◽  
Salmo Salar ◽  
Gadus Morhua ◽  
Clupea Harengus ◽  
Fish Stock ◽  
The Baltic Sea ◽  
Atlantic Salmon Salmo Salar ◽  
Reproductive Disorder ◽  
The Baltic

Abstract Mikkonen, J., Keinänen, M., Casini, M., Pönni, J., and Vuorinen, P. J. 2011. Relationships between fish stock changes in the Baltic Sea and the M74 syndrome, a reproductive disorder of Atlantic salmon (Salmo salar). – ICES Journal of Marine Science, 68: 2134–2144. The M74 syndrome of Baltic salmon (Salmo salar), which appears as increased yolk-sac fry mortality (YSFM), impairs the reproduction of salmon stocks. Changes in the prey stocks of Baltic salmon in its two feeding areas, the southern Baltic Proper (BPr), where sprat (Sprattus sprattus) was the main prey species during the high incidence of M74, and the Bothnian Sea, where herring (Clupea harengus) is the dominant species, were analysed in relation to salmon growth and size and in relation to the incidence of M74. The high condition factor (CF > 1.05) of prespawning salmon predicted high YSFM. From the various stock factors of sprat and herring in the southern BPr, the biomass of sprat had the strongest positive relationships with the CF of prespawning salmon, and the total prey biomass with YSFM. It is concluded that the ample but unbalanced food resources for salmon in the BPr, primarily sprat, induce M74. By reducing the fishing pressure on cod (Gadus morhua) and by more effectively managing the sprat fishery in years when the cod stock is weak, the incidence of the M74 syndrome could be reduced and even prevented.

Temporal changes in harvesting dynamics of Canadian inshore fisheries for northern Atlantic cod, Gadus morhua

2000 ◽  
Vol 57 (4) ◽  
pp. 805-814 ◽  
Author(s):  
Jeffrey A Hutchings ◽  
Mark Ferguson
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Fishing Effort ◽  
Temporal Changes ◽  
Catch Rate ◽  
Fish Stock ◽  
Small Fish ◽  
Trap Design ◽  
Northern Atlantic ◽  
Unreported Catches

We quantified temporal changes in catch rate, fishing effort, and catch misreporting for two sectors of the fixed-gear fishery for Newfoundland's northern Atlantic cod, Gadus morhua, from 1980 to 1991, the year preceding the stock's commercial fishing moratorium. Over the 12-year period, fishermen reported catch rate declines of 40 and 75% in the trap and gillnet fisheries, respectively, associated with significant increases in nominal fishing effort. Additional changes to effort included smaller gillnet and trap mesh sizes, larger traps, longer soak times, and modifications to trap design to increase catch retention probabilities. Compared with the early 1980s, unreported catches among inshore fishermen may have trebled by the late 1980s and early 1990s due to longer gillnet soak times, increased gear selectivity for small fish, and declining availability of fish of marketable size. These patterns in harvesting dynamics are consistent with the hypothesis that the decline of northern cod was gradual and that increased rates of catch misreporting contributed to increases in fishing mortality. The concomitants of declining fixed-gear catch rate, increasing quantitative and qualitative fishing effort, increased selectivity for smaller fish, and increasing levels of unreported catches may represent general correlates of imminent fish stock collapses.

scholarly journals Transcriptome analysis of gill tissue of Atlantic cod Gadus morhua L. from the Baltic Sea

2015 ◽  
Vol 23 ◽  
pp. 37-40 ◽  
Author(s):  
Magdalena Małachowicz ◽  
Agnieszka Kijewska ◽  
Roman Wenne
Keyword(s):  
Baltic Sea ◽  
Transcriptome Analysis ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Gill Tissue ◽  
The Baltic Sea ◽  
The Baltic

Biological indications of contaminant exposure in Atlantic cod (Gadus morhua) in the Baltic Sea

2008 ◽  
Vol 65 (6) ◽  
pp. 1122-1134 ◽  
Author(s):  
Sabine Schnell ◽  
Doris Schiedek ◽  
Rolf Schneider ◽  
Lennart Balk ◽  
Pekka J. Vuorinen ◽  
...  
Keyword(s):  
Baltic Sea ◽  
Organic Contaminants ◽  
Gadus Morhua ◽  
Polychlorinated Biphenyl ◽  
Atlantic Cod ◽  
Human Impacts ◽  
Toxic Substances ◽  
The Baltic Sea ◽  
Contaminant Exposure ◽  
The Baltic

The Baltic Sea is exposed to severe human impacts. Besides eutrophication and overfishing, a variety of chemical contaminants threaten the health of fish. During a cruise in December 2001, Atlantic cod ( Gadus morhua ) were collected in the western and southern Baltic Sea, somatic condition factors were estimated, and different biomarkers of contaminant exposure were analysed. Additionally, various polychlorinated biphenyl congeners and organochlorine pesticides were measured in cod liver as more general indicators of pollution, not necessarily as the causative agents for biomarker signals. In most specimens, hepatic ethoxyresorufin-O-deethylase activity and bile 1-OH pyrene, a common polycyclic aromatic hydrocarbon metabolite, were detectable. Both features indicate an induction of the CYP1A biotransformation system in response to toxic substances. The increased occurrence of DNA adducts in some of the specimens also indicates the presence of genotoxic substances. Acetylcholinesterase was inhibited, an indication of exposure to organophosphates, carbamates, or certain heavy metals, particularly in specimens taken at Wismar Bay and off the Lithuanian coast. In general, spatial differences in the biomarker responses as well as in contaminant loads were found, suggesting differences in physiologically active concentrations and mixtures of organic contaminants in this ecosystem.

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