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

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.

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

ICES Journal of Marine Science ◽

10.1093/icesjms/fsm124 ◽

2007 ◽

Vol 64 (8) ◽

pp. 1603-1606 ◽

Cited By ~ 26

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.

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Using data storage tags to link otolith macro- structure in Baltic cod Gadus morhua with environmental conditions

Marine Ecology Progress Series ◽

10.3354/meps07876 ◽

2009 ◽

Vol 378 ◽

pp. 161-170 ◽

Cited By ~ 20

Author(s):

K Hüssy ◽

B Nielsen ◽

H Mosegaard ◽

LW Clausen

Keyword(s):

Data Storage ◽

Environmental Conditions ◽

Gadus Morhua ◽

Data Storage Tags ◽

Using Data ◽

Baltic Cod

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Changes in size-at-maturity of Baltic cod (Gadus morhua) during a period of large variations in stock size and environmental conditions

Fisheries Research ◽

10.1016/s0165-7836(99)00021-1 ◽

1999 ◽

Vol 41 (3) ◽

pp. 285-295 ◽

Cited By ~ 54

Author(s):

M. Cardinale ◽

J. Modin

Keyword(s):

Environmental Conditions ◽

Gadus Morhua ◽

Size At Maturity ◽

Stock Size ◽

Baltic Cod

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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

ICES Journal of Marine Science ◽

10.1093/icesjms/fsu124 ◽

2014 ◽

Vol 72 (2) ◽

pp. 686-696 ◽

Cited By ~ 33

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.

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

ICES Journal of Marine Science ◽

10.1093/icesjms/fsw178 ◽

2016 ◽

Vol 74 (5) ◽

pp. 1344-1355 ◽

Cited By ~ 8

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.

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Hydrographic influence on the spawning habitat suitability of western Baltic cod (Gadus morhua)

ICES Journal of Marine Science ◽

10.1093/icesjms/fss136 ◽

2012 ◽

Vol 69 (10) ◽

pp. 1736-1743 ◽

Cited By ~ 10

Author(s):

K. Hüssy ◽

H.-H. Hinrichsen ◽

B. Huwer

Keyword(s):

Water Temperature ◽

Environmental Conditions ◽

Habitat Suitability ◽

Gadus Morhua ◽

Reproductive Potential ◽

Spawning Season ◽

Spawning Habitat ◽

Egg Survival ◽

The Impact ◽

Baltic Cod

Abstract Hüssy, K., Hinrichsen, H.-H., and Huwer, B. 2012. Hydrographic influence on the spawning habitat suitability of western Baltic cod (Gadus morhua) – ICES Journal of Marine Science, 69: 1736–1743. Recruitment variability of marine fish is influenced by the reproductive potential of the stock (i.e. stock characteristics and abundance) and the survival of early life stages, mediated by environmental conditions of both a physical (water temperature, salinity and oxygen conditions, ocean currents) and a biological nature (i.e. food, predators). The objective of this study is to assess the importance of variability in environmental conditions within different western Baltic cod spawning grounds for egg survival. Habitat identification was based on environmental threshold levels for egg survival and development and ambient hydrographical conditions at different times during the spawning season. The long-term resolution of environmental conditions allowing survival of western Baltic cod eggs indicates that favourable conditions predominantly occurred during the late spawning season in April/May, while minimum survival rates could be expected from January to March. Unsuitable time periods and habitats exhibiting the highest mortality rates are exclusively characterized by ambient water temperatures below the critical survival threshold. Despite the strong influence of water temperature on habitat suitability, the impact of habitat suitability on recruitment was not clearly defined, suggesting that other mechanisms regulate year class strength.

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