Using alternative biological information in stock assessment: condition-corrected natural mortality of Eastern Baltic cod

Casini, Michèle; Eero, Margit; Carlshamre, Sofia; Lövgren, Johan

doi:10.1093/icesjms/fsw117

Cited by 33 publications

(27 citation statements)

References 23 publications

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“…Moreover, the strong effect of pelagic prey biomass on cod condition found in our study supports the recent ICES Advice to limit the fishery after pelagic fish in the current main distribution area of cod [80] to preserve important food resources for cod. Experimental studies have evidenced that cod with low condition have a higher chance to die because of starvation [6], and therefore, a negative effect on cod survival could also be expected for the Baltic Sea [81]. Our results evidence the necessity to link tightly environmental and fisheries management issues to assure the health of fish populations and the profitability of the fishery.…”

Section: Resultsmentioning

confidence: 67%

Hypoxic areas, density-dependence and food limitation drive the body condition of a heavily exploited marine fish predator

et al. 2016

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Investigating the factors regulating fish condition is crucial in ecology and the management of exploited fish populations. The body condition of cod (Gadus morhua) in the Baltic Sea has dramatically decreased during the past two decades, with large implications for the fishery relying on this resource. Here, we statistically investigated the potential drivers of the Baltic cod condition during the past 40 years using newly compiled fishery-independent biological data and hydrological observations. We evidenced a combination of different factors operating before and after the ecological regime shift that occurred in the Baltic Sea in the early 1990s. The changes in cod condition related to feeding opportunities, driven either by density-dependence or food limitation, along the whole period investigated and to the fivefold increase in the extent of hypoxic areas in the most recent 20 years. Hypoxic areas can act on cod condition through different mechanisms related directly to species physiology, or indirectly to behaviour and trophic interactions. Our analyses found statistical evidence for an effect of the hypoxia-induced habitat compression on cod condition possibly operating via crowding and density-dependent processes. These results furnish novel insights into the population dynamics of Baltic Sea cod that can aid the management of this currently threatened population.

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Section: Resultsmentioning

confidence: 67%

Hypoxic areas, density-dependence and food limitation drive the body condition of a heavily exploited marine fish predator

et al. 2016

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“…All mechanisms may lead to an increase in natural mortality. The critical Fulton condition factor where cod are considered dying is defined in Casini et al , 2016a based on findings of Dutil and Lambert, 2000 …”

Section: Discussionmentioning

confidence: 99%

Physiological condition of Eastern Baltic cod, Gadus morhua, infected with the parasitic nematode Contracaecum osculatum

Ryberg

Skov

Vendramin

et al. 2020

Conservation Physiology

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Establishing relationships between parasite infection and physiological condition of the host can be difficult and therefore are often neglected when describing factors causing population declines. Using the parasite–host system between the parasitic nematode Contracaecum osculatum and the Eastern Baltic cod Gadus morhua, we here shed new light on how parasite load may relate to the physiological condition of a transport host. The Eastern Baltic cod is in distress, with declining nutritional conditions, disappearance of the larger fish, high natural mortality and no signs of recovery of the population. During the latest decade, high infection levels with C. osculatum have been observed in fish in the central and southern parts of the Baltic Sea. We investigated the aerobic performance, nutritional condition, organ masses, and plasma and proximate body composition of wild naturally infected G. morhua in relation to infection density with C. osculatum. Fish with high infection densities of C. osculatum had (i) decreased nutritional condition, (ii) depressed energy turnover as evidenced by reduced standard metabolic rate, (iii) reduction in the digestive organ masses, and alongside (iv) changes in the plasma, body and liver composition, and fish energy source. The significantly reduced albumin to globulin ratio in highly infected G. morhua suggests that the fish suffer from a chronic liver disease. Furthermore, fish with high infection loads had the lowest Fulton’s condition factor. Yet, it remains unknown whether our results steam from a direct effect of C. osculatum, or because G. morhua in an already compromised nutritional state are more susceptible towards the parasite. Nevertheless, impairment of the physiological condition can lead to reduced swimming performance, compromising foraging success while augmenting the risk of predation, potentially leading to an increase in the natural mortality of the host. We hence argue that fish–parasite interactions must not be neglected when implementing and refining strategies to rebuild deteriorating populations.

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“…In some cases, fish samples were obtained from commercial fisheries that gutted fish prior to landing. For those, correction factors (Casini et al, 2016a) were applied. For purposes of this analysis, K was grouped into two categories: low (K < 9) and high (K ≥ 9).…”

Section: Methodsmentioning

confidence: 99%

Effect of Marine Hypoxia on Baltic Sea Cod Gadus morhua: Evidence From Otolith Chemical Proxies

Limburg

Casini

2018

Front. Mar. Sci.

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The Baltic Sea contains the world's largest anthropogenic deoxygenated zone, with increasing episodes and areal extent of hypoxia/anoxia. Atlantic cod in the Baltic has suffered a loss in condition which has been attributed mainly to hypoxia. Otoliths, the aragonitic structures that form part of the hearing/balance system in fishes, accumulate Mn in the presence of hypoxia and other reducing environments. Otoliths grow over the lifetime of fishes, and thus lifelong records of hypoxia exposure exist for each individual fish. However, otolith Mn/Ca ratios are also sensitive to growth effects. We tested a new proxy to at least partially account for growth: Mn/Mg, since Mg levels reflect metabolic activity but not hypoxia. This and other elemental proxies were parsed annually from the otoliths to reconstruct lifetime histories of mean, maximum, and cumulative values of this proxy as well as others (Sr/Ca) that inform us about salinity conditions. We analyzed cod from five different time periods: Neolithic (4500 YBP, a normoxic baseline), 1980s, 1990s, 2000s, and 2010s-under different hypoxia intensities, assessing fish growth and condition in relation to hypoxia experience recorded by otolith proxies. Fish growth decreased with increasing hypoxia exposure; condition at capture (measured by Fulton's K index) showed a strongly positive relation to growth indexed by magnesium (Mg/Ca). We conclude that cod otolith chemistry proxies not only inform about the hypoxia, growth, and metabolic status of cod, retrospectively throughout life, but also reflect the worsening situation for cod in the Baltic.

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Using alternative biological information in stock assessment: condition-corrected natural mortality of Eastern Baltic cod

Cited by 33 publications

References 23 publications

Hypoxic areas, density-dependence and food limitation drive the body condition of a heavily exploited marine fish predator

Hypoxic areas, density-dependence and food limitation drive the body condition of a heavily exploited marine fish predator

Physiological condition of Eastern Baltic cod, Gadus morhua, infected with the parasitic nematode Contracaecum osculatum

Effect of Marine Hypoxia on Baltic Sea Cod Gadus morhua: Evidence From Otolith Chemical Proxies

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