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 Factors affecting rule compliance with mesh size regulations in the Baltic cod trawl fishery

2007 ◽  
Vol 64 (8) ◽  
pp. 1603-1606 ◽  
Author(s):  
Petri Suuronen ◽  
Vesa Tschernij ◽  
Pekka Jounela ◽  
Daniel Valentinsson ◽  
P-O. Larsson
Keyword(s):  
Gadus Morhua ◽  
Management Practice ◽  
Mesh Size ◽  
Factors Affecting ◽  
Trawl Fishery ◽  
Management Measures ◽  
Gradual Introduction ◽  
Minimum Landing Size ◽  
The Baltic ◽  
Baltic Cod

Abstract Suuronen, P., Tschernij, V., Jounela, P., Valentinsson, D., and Larsson, P-O. 2007. Factors affecting rule compiance with mesh size regulations in the Baltic cod trawl fishery. – ICES Journal of Marine Science, 64: 1603–1606. In this study, we evaluate the efficiency and applicability of a series of gear-based management measures, enforced since 1990, whose purpose was to improve size selectivity in the trawl fishery for Baltic cod (Gadus morhua). In general, our study revealed that these measures had no marked effect on the capture and discard of young cod. Legal and illegal manipulation of selective codends was widespread. The adoption of a codend design that offered a modest increase in selectivity, but had a good match with the legislated minimum landing size (MLS), led to greater compliance, demonstrating that a mismatch between MLS and selectivity should be avoided. It was also obvious that, generally, the fishing industry did not tolerate large short-term losses. Our evaluation is that overly ambitious rules will be circumvented, and frequent and incoherent changes in the regulations represent bad management practice. A gradual introduction of restrictions and participation by fishers in the decision-making process will increase compliance.

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.

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 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.

scholarly journals Condition indices of Atlantic cod (Gadus morhua) biased by capturing method

2012 ◽  
Vol 69 (10) ◽  
pp. 1781-1788 ◽  
Author(s):  
Mikael Ovegård ◽  
Kim Berndt ◽  
Sven-Gunnar Lunneryd
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Geographical Area ◽  
Lower Growth ◽  
Fish Stocks ◽  
Underlying Causes ◽  
The Difference ◽  
Condition Indices ◽  
The Baltic ◽  
Size At Age

Abstract Ovegård, M., Berndt, K., and Lunneryd, S-G. 2012. Condition indices of Atlantic cod (Gadus morhua) biased by capturing method. – ICES Journal of Marine Science, 69: 1781–1788. In studies evaluating the condition and general health status of fish stocks, the method used for catching the fish is seldom considered as a factor of importance. In this study, condition indices were compared between cod caught in pots, gillnets, and on hooks in the same geographical area. The results showed that cod (Gadus morhua) caught on baited gear types (pots and hooks) generally displayed a lower condition and an older age (i.e. suggesting a lower growth rate) compared to cod caught in gillnets. It is unclear whether these results merely illustrate divergent behavioural responses in fish originating from one single population, or if these divergent behavioural components represent distinct subpopulations displaying different mean conditions and growth rates. Regardless of the underlying causes, the results not only show that parts of the Baltic cod stock are in extremely poor condition, they also indicate that different gear types used in the same area could target similar-sized conspecifics exhibiting large differences in condition and size-at-age. The potential impact of the difference in condition between the pots and other gear types could hamper the implementation of the cod pot as a potentially seal-safe and sustainable fishing method.

Understanding limits to cod and haddock separation using size selectivity in a multispecies trawl fishery: an application of FISHSELECT

2011 ◽  
Vol 68 (5) ◽  
pp. 927 ◽  
Author(s):  
Manu Sistiaga ◽  
Bent Herrmann ◽  
Kåre N. Nielsen ◽  
Roger B. Larsen
Keyword(s):  
Gadus Morhua ◽  
Barents Sea ◽  
Atlantic Cod ◽  
Morphological Characteristics ◽  
Melanogrammus Aeglefinus ◽  
Size Selectivity ◽  
Sea Trial ◽  
Trawl Fishery ◽  
The Barents Sea ◽  
Morphological Differences

This investigation demonstrates how a multidisciplinary approach based on the FISHSELECT framework, sea trial data, underwater recordings, and laboratory investigations of netting can be applied to size selectivity studies and related management issues. We studied the morphological characteristics of Atlantic cod ( Gadus morhua ) and haddock ( Melanogrammus aeglefinus ) in the Barents Sea bottom trawl fishery. The differences between the L50 values (i.e., the size at which a fish has a 50% chance of being retained) that were recorded for the two species during sea trials can to a large extent be explained by the morphological differences between them. Because of these morphological differences, L50 is always larger for cod than for haddock with the grid and codend setup commonly used in the area. While catch separation of cod and haddock is a management objective in the Barents Sea, we demonstrate that the morphological differences between the species and the grid and codend setup in force today limit achievable differences in L50 to 5.5 cm. Furthermore, we show that for this fishery, the scope for increasing L50 differences between these species by changing the mesh shape configuration of the codend is minimal.

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