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.

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.

Modeling environmentally driven uncertainties in Baltic cod (Gadus morhua) management by Bayesian influence diagrams

1999 ◽  
Vol 56 (4) ◽  
pp. 629-641 ◽  
Author(s):  
S Kuikka ◽  
M Hildén ◽  
H Gislason ◽  
S Hansson ◽  
H Sparholt ◽  
...  
Keyword(s):  
Environmental Conditions ◽  
Gadus Morhua ◽  
Saline Water ◽  
Mesh Size ◽  
Influence Diagrams ◽  
Large Variability ◽  
Trawl Fishery ◽  
Management Advice ◽  
Estimation Of Uncertainties ◽  
Baltic Cod

The large variability in Baltic cod (Gadus morhua) recruitment has been attributed both to environmental factors dependent on the inflow of saline water (oxygen and salinity in spawning deeps) and to the size of the spawning stock. Due to the complex interactions between hydrographic and biological processes, future recruitment levels of cod will remain highly uncertain and increase uncertainties in stock predictions and management advice. We assessed the effects of the exploitation level and mesh size used by a trawl fishery on some variables of management interest under different environmental conditions. The modeling consisted of three separate steps: (i) modeling of selectivity, (ii) estimation of uncertainties by Monte Carlo simulations, and (iii) decision analysis by Bayesian influence diagrams, focusing on the structural uncertainties and model selection. Realistic assumptions of environmental conditions and present fishing mortality rates suggest that the current Baltic cod fishery is unsustainable. We use our approach to identify robust management measures that reduce the risk of overfishing and the sensitivity to management information. The value of information analysis demonstrates the advantages of a larger mesh size as a management measure.

Improving selectivity of the Baltic cod pelagic trawl fishery: Experiments to assess the next step

2010 ◽  
Vol 103 (1-3) ◽  
pp. 40-47 ◽  
Author(s):  
Niels Madsen ◽  
Vesa Tschernij ◽  
Renè Holst
Keyword(s):  
Trawl Fishery ◽  
The Baltic ◽  
Baltic Cod

scholarly journals Deoxygenation impacts on Baltic Sea cod: Dramatic declines in ecosystem services of an iconic keystone predator

AMBIO ◽  
2021 ◽  
Author(s):  
Alessandro Orio ◽  
Yvette Heimbrand ◽  
Karin Limburg
Keyword(s):  
Ecosystem Services ◽  
Baltic Sea ◽  
Gadus Morhua ◽  
Generalized Additive Model ◽  
Additive Model ◽  
Maximum Length ◽  
The Baltic Sea ◽  
Hypoxic Zone ◽  
The Baltic ◽  
Baltic Cod

AbstractThe intensified expansion of the Baltic Sea’s hypoxic zone has been proposed as one reason for the current poor status of cod (Gadus morhua) in the Baltic Sea, with repercussions throughout the food web and on ecosystem services. We examined the links between increased hypoxic areas and the decline in maximum length of Baltic cod, a demographic proxy for services generation. We analysed the effect of different predictors on maximum length of Baltic cod during 1978–2014 using a generalized additive model. The extent of minimally suitable areas for cod (oxygen concentration ≥ 1 ml l−1) is the most important predictor of decreased cod maximum length. We also show, with simulations, the potential for Baltic cod to increase its maximum length if hypoxic areal extent is reduced to levels comparable to the beginning of the 1990s. We discuss our findings in relation to ecosystem services affected by the decrease of cod maximum length.

scholarly journals Developing Baltic cod recruitment models. II. Incorporation of environmental variability and species interaction

2001 ◽  
Vol 58 (8) ◽  
pp. 1534-1556 ◽  
Author(s):  
Friedrich W Köster ◽  
Hans-Harald Hinrichsen ◽  
Michael A St. John ◽  
Dietrich Schnack ◽  
Brian R MacKenzie ◽  
...  
Keyword(s):  
Egg Production ◽  
Gadus Morhua ◽  
Environmental Variability ◽  
Species Interaction ◽  
Larval Transport ◽  
Factors Affecting ◽  
Oxygen Conditions ◽  
Modelling Studies ◽  
Spawning Sites ◽  
Baltic Cod

We investigate whether a process-oriented approach based on the results of field, laboratory, and modelling studies can be used to develop a stock–environment–recruitment model for Central Baltic cod (Gadus morhua). Based on exploratory statistical analysis, significant variables influencing survival of early life stages and varying systematically among spawning sites were incorporated into stock–recruitment models, first for major cod spawning sites and then combined for the entire Central Baltic. Variables identified included potential egg production by the spawning stock, abiotic conditions affecting survival of eggs, predation by clupeids on eggs, larval transport, and cannibalism. Results showed that recruitment in the most important spawning area, the Bornholm Basin, during 1976–1995 was related to egg production; however, other factors affecting survival of the eggs (oxygen conditions, predation) were also significant and when incorporated explained 69% of the variation in 0-group recruitment. In other spawning areas, variable hydrographic conditions did not allow for regular successful egg development. Hence, relatively simple models proved sufficient to predict recruitment of 0-group cod in these areas, suggesting that key biotic and abiotic processes can be successfully incorporated into recruitment models.

scholarly journals Post-smolt survival of Baltic salmon in context to changing environmental conditions and predators

2016 ◽  
Vol 74 (5) ◽  
pp. 1344-1355 ◽  
Author(s):  
Kevin D. Friedland ◽  
Johan Dannewitz ◽  
Atso Romakkaniemi ◽  
Stefan Palm ◽  
Henni Pulkkinen ◽  
...  
Keyword(s):  
Environmental Conditions ◽  
Coastal Waters ◽  
Gadus Morhua ◽  
Environmental Parameters ◽  
Predation Pressure ◽  
First Year ◽  
Central Basin ◽  
The Baltic ◽  
Latitudinal Range ◽  
Baltic Cod

The survival of Baltic salmon Salmo salar during the first year at sea (post-smolt stage) has declined since the beginning of the 1990s. In this analysis, we complement previous studies on possible causes of this decline by considering a suite of environmental parameters, potential change in predation pressure, and post-smolt growth. Marine survival estimates were found to be negatively correlated with temperature, indicating that warming conditions have not favoured survival. Survival was also found to be positively correlated with dissolved oxygen levels and regionally related to shifts in salinity. These relationships were further studied in context to the potential predation on post-smolts by one of the main piscivores in the Baltic, Eastern Baltic cod (Gadus morhua callarias). Concomitant with changes in environmental conditions, Baltic cod has changed its latitudinal range, moving northward in the Baltic, possibly in response to warming conditions. These changes lead us to hypothesize that predation pressure on salmon may have increased in recent years as cod has now occupied habitats used by salmon post-smolts during their southward feeding migrations. This predation may have been intensified as a result of anoxic conditions in the central basin by concentrating predation interactions in coastal waters and/or the upper water column typically occupied by salmon post-smolts. Indicators of post-smolt growth were applied to test the alternate hypothesis that mortality is growth-mediated; these indicators lacked a time series trend, which supports the contention that shifting predation pressure rather than feeding opportunities is responsible for the decline in post-smolt survival in Baltic salmon.

Early embryonic cleavage pattern, hatching success, and egg-lipid fatty acid composition: comparison between two cod (Gadus morhua) stocks

1997 ◽  
Vol 54 (10) ◽  
pp. 2410-2416 ◽  
Author(s):  
J Pickova ◽  
P C Dutta ◽  
P -O Larsson ◽  
A Kiessling
Keyword(s):  
Gadus Morhua ◽  
Hatching Success ◽  
Hatching Rate ◽  
Cleavage Pattern ◽  
Egg Viability ◽  
Lipid Fatty Acid ◽  
Embryonic Cleavage ◽  
The Baltic ◽  
Lipid Fatty Acid Composition ◽  
Baltic Cod

Baltic cod (Gadus morhua), from a brackish environment, were compared with oceanic (Skagerrak) cod in terms of early embryonic cleavage pattern, hatching success, and egg-lipid fatty acid composition. The influence of diet on these variables was investigated by analysing eggs from the Baltic stock, caught during three successive years and given controlled food for 24, 7, and 2 months, respectively, before the experiment commenced. Skagerrak cod eggs contained twice as much arachidonic acid (AA) in the phospholipid (PL) fraction as eggs from the Baltic cod, regardless of the length of time the Baltic cod had been kept in captivity and fed a control diet. Correlation between hatching rate and docosahexaenoic (DHA; 22:6n-3)/ eicosapentaenoic acid (EPA; 20:5n-3) ratio was significant (r2 = 0.56) as well as hatching rate and AA content of the PL fraction (r2 = 0.61). Symmetry during development, which was correlated to egg viability, was higher for eggs from Skagerrak than those from the Baltic stock. We suggest that AA content and DHA/EPA ratio of the PL fraction are important factors influencing egg viability and possibly also egg symmetry.\b Further, it appears that the factor(s) influencing the composition of the PL fraction is mostly related to stock rather than to diet.

Escape windows to improve the size selectivity in the Baltic cod trawl fishery

2002 ◽  
Vol 57 (3) ◽  
pp. 223-235 ◽  
Author(s):  
Niels Madsen ◽  
René Holst ◽  
Leslie Foldager
Keyword(s):  
Size Selectivity ◽  
Trawl Fishery ◽  
The Baltic ◽  
Baltic Cod
Sign in / Sign up

Export Citation Format

Share Document