Effects of varying natural mortality and selectivity on the assessment of eastern Baltic cod (Gadus morhua Linnaeus, 1758) stock

2016 ◽  
Vol 32 (6) ◽  
pp. 1032-1040 ◽  
Author(s):  
J. Horbowy
Keyword(s):  
Gadus Morhua ◽  
Natural Mortality ◽  
Eastern Baltic ◽  
Baltic Cod

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

2020 ◽  
Vol 8 (1) ◽  
Author(s):  
Marie Plambech Ryberg ◽  
Peter V Skov ◽  
Niccolò Vendramin ◽  
Kurt Buchmann ◽  
Anders Nielsen ◽  
...  
Keyword(s):  
Gadus Morhua ◽  
Physiological Condition ◽  
Parasitic Nematode ◽  
Nutritional Condition ◽  
Natural Mortality ◽  
Risk Of Predation ◽  
High Infection ◽  
Contracaecum Osculatum ◽  
Eastern Baltic ◽  
Baltic Cod

Abstract 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.

Robustness of egg production methods as a fishery independent alternative to assess the Eastern Baltic cod stock (Gadus morhua callarias L.)

2012 ◽  
Vol 117-118 ◽  
pp. 75-85 ◽  
Author(s):  
Gerd Kraus ◽  
Hans-Harald Hinrichsen ◽  
Rüdiger Voss ◽  
Eske Teschner ◽  
Jonna Tomkiewicz ◽  
...  
Keyword(s):  
Egg Production ◽  
Gadus Morhua ◽  
Production Methods ◽  
Eastern Baltic ◽  
Baltic Cod

scholarly journals Slave to the rhythm: seasonal signals in otolith microchemistry reveal age of eastern Baltic cod (Gadus morhua)

2015 ◽  
Vol 73 (4) ◽  
pp. 1019-1032 ◽  
Author(s):  
K. Hüssy ◽  
J. Gröger ◽  
F. Heidemann ◽  
H.-H. Hinrichsen ◽  
L. Marohn
Keyword(s):  
North Sea ◽  
Gadus Morhua ◽  
Statistical Significance ◽  
Structural Break ◽  
Age Determination ◽  
Element Concentrations ◽  
Visual Contrast ◽  
Growth Zones ◽  
Eastern Baltic ◽  
Baltic Cod

Abstract Annual growth zones in cod otoliths from the eastern Baltic stock are less discrete than in other cod stocks leading to biased age reading, which recently led to a failure of age-based assessment in the eastern Baltic cod stock. In this study, we explored the applicability of minor and trace element patterns in cod otoliths for age determination. By first identifying elements of interest in a stock without ageing problems, western Baltic cod, we then tested their applicability on another stock without ageing problems, North Sea cod, and finally applied this knowledge to estimate age of eastern Baltic cod. In western Baltic cod, matching patterns with respect to occurrence of minima and maxima in both otolith opacity and element concentrations were found for Cu, Zn, and Rb, and inverse patterns with Mg and Mn. No match was found for Pb, Ba, and Sr. In the test stock, the North Sea cod, the same patterns in Cu, Zn, Rb, Mg, and Mn signals occurred. All eastern Baltic cod with low visual contrast between growth zones exhibited clearly defined synchronous cycles in Cu, Zn, Rb and Pb. Using a combined finite differencing method and structural break models approach, the statistical significance of the local profile minima were identified, based on which their age could be estimated. Despite extensive environmental differences between the three areas examined, the element concentrations of Cu, Zn, and Rb were strongly correlated in all individuals with similar correlations in all three areas, suggesting that the incorporation mechanisms are the same for these elements and independent of environmental concentrations.

scholarly journals Egg production of Baltic cod (Gadus morhua) in relation to variable sex ratio, maturity, and fecundity

2002 ◽  
Vol 59 (12) ◽  
pp. 1908-1920 ◽  
Author(s):  
Gerd Kraus ◽  
Jonna Tomkiewicz ◽  
Friedrich W Köster
Keyword(s):  
Sex Ratio ◽  
Egg Production ◽  
Gadus Morhua ◽  
Reproductive Potential ◽  
Relative Fecundity ◽  
Spawning Stock ◽  
Class Strength ◽  
The Difference ◽  
Eastern Baltic ◽  
Baltic Cod

Observed fluctuations in relative fecundity of Eastern Baltic cod (Gadus morhua L.) were related to food availability during the main feeding period and were used to develop a predictive model that explained 72% of the interannual variations in fecundity. Time series of sex ratios, maturity ogives, and relative fecundity were combined with mean weights-at-age and stock sizes from an analytical multispecies model to estimate the potential egg production (PEP). Relationships between PEP and independent estimates of realized daily and seasonal egg production from egg surveys were highly significant. The difference between estimates of potential and realized seasonal egg production was of a magnitude corresponding to the expected loss of eggs as a result of atresia, fertilization failure, and early egg mortality. The removal of interannual variability in sex ratio, maturity, and fecundity on estimates of PEP deteriorated the relationships in all three cases. PEP proved to be superior to spawning stock biomass as measure of the reproductive potential in a stock-recruitment relationship of Eastern Baltic cod. PEP in combination with the reproductive volume explained 61% of the variation in year-class strength at age 2.

scholarly journals Stable Isotope Evidence for Late Medieval (14th–15th C) Origins of the Eastern Baltic Cod (Gadus morhua) Fishery

PLoS ONE ◽  
2011 ◽  
Vol 6 (11) ◽  
pp. e27568 ◽  
Author(s):  
David C. Orton ◽  
Daniel Makowiecki ◽  
Tessa de Roo ◽  
Cluny Johnstone ◽  
Jennifer Harland ◽  
...  
Keyword(s):  
Stable Isotope ◽  
Gadus Morhua ◽  
Late Medieval ◽  
Isotope Evidence ◽  
Eastern Baltic ◽  
Baltic Cod

Development of international fisheries for the eastern Baltic cod (Gadus morhua) from the late 1880s until 1938

2007 ◽  
Vol 87 (2-3) ◽  
pp. 155-166 ◽  
Author(s):  
Margit Eero ◽  
Brian R. MacKenzie ◽  
Hrefna M. Karlsdóttir ◽  
Ritma Gaumiga
Keyword(s):  
Gadus Morhua ◽  
Eastern Baltic ◽  
Baltic Cod ◽  
International Fisheries

scholarly journals Changes in population depth distribution and oxygen stratification are involved in the current low condition of the eastern Baltic Sea cod (<i>Gadus morhua</i>)

2021 ◽  
Vol 18 (4) ◽  
pp. 1321-1331
Author(s):  
Michele Casini ◽  
Martin Hansson ◽  
Alessandro Orio ◽  
Karin Limburg
Keyword(s):  
Baltic Sea ◽  
Body Condition ◽  
Gadus Morhua ◽  
Depth Distribution ◽  
Low Oxygen ◽  
Commercial Fish ◽  
Spatial Overlap ◽  
The Past ◽  
Eastern Baltic ◽  
Baltic Cod

Abstract. During the past 20 years, hypoxic areas have expanded rapidly in the Baltic Sea, which has become one of the largest marine “dead zones” in the world. At the same time, the most important commercial fish population of the region, the eastern Baltic cod, has experienced a drastic reduction in mean body condition, but the processes behind the relation between deoxygenation and condition remain elusive. Here we use extensive long-term monitoring data on cod biology and distribution as well as on hydrological variations to investigate the processes that relate deoxygenation and cod condition during the autumn season. Our results show that the depth distribution of cod has increased during the past 4 decades at the same time of the expansion, and shallowing, of waters with oxygen concentrations detrimental to cod performance. This has resulted in a progressively increasing spatial overlap between the cod population and low-oxygenated waters after the mid-1990s. This spatial overlap and the actual oxygen concentration experienced by cod therein statistically explained a large proportion of the changes in cod condition over the years. These results complement previous analyses on fish otolith microchemistry that also revealed that since the mid-1990s, cod individuals with low condition were exposed to low-oxygen waters during their life. This study helps to shed light on the processes that have led to a decline of the eastern Baltic cod body condition, which can aid the management of this population currently in distress. Further studies should focus on understanding why the cod population has moved to deeper waters in autumn and on analyzing the overlap with low-oxygen waters in other seasons to quantify the potential effects of the variations in physical properties on cod biology throughout the year.

Sign in / Sign up

Export Citation Format

Share Document