Prediction of vertical distribution and ambient development temperature of Baltic cod, <i>Gadus morhua</i> L., eggs

Wieland, Kai; Jarre-Teichmann, A.

doi:10.1046/j.1365-2419.1997.00038.x

Cited by 34 publications

(39 citation statements)

References 15 publications

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“…An explanation for the different feeding behaviour is a changed vertical overlap between predator and prey, due to significant alterations in the hydrographic regime of the Bornholm Basin after the major inflow in early 1993 (Matthaus & Lass 1995). For cod eggs a shift in the vertical distribution to shallower water layers as a consequence of the inflow has been previously described (Wieland & Jarre-Teichmann 1997), reducing the vertical overlap with clupeid predators during their daily feeding period (Koster & Mollmann 2000). A corresponding change in the vertical distribution of sprat eggs is indicated in Fig.…”

Section: Discussionmentioning

confidence: 95%

Egg cannibalism in Baltic sprat Sprattus sprattus

Köster¹,

Möllmann²

2000

Mar. Ecol. Prog. Ser.

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Throughout the last 2 decades a shift from a cod-to a sprat-dominated system occurred in the upper trophic levels of the Central Baltic Sea. This was caused by a decline in the cod stock, due to recruitment failure and high fishing intens~ty, resulting in a decrease in predation pressure on sprat. Concurrently with the lowest cod stock size on record, sprat reached biomass values of above 2 X 106 t in 1992, being relatively stable afterwards. Besides predation mortality through cod and in recent years also an increasing fishing pressure, cannibalism on eggs may be a compensatory process limiting the reproductive success of sprat and hence contributing to the population regulation in the Central Baltic. Based on sprat stomach sampling on 21 cruises between March 1988 and July 1996 cannibalism on sprat eggs was investigated in the Bornholrn Basin, one of the main spawning areas of Central Baltic sprat. Using a model of gastric evacuation to estimate daily food intake rates and a Virtual PopulationIExtended Survivor Analysis for computing predator population sizes, egg cannibalism rates were estimated. These were compared to egg abundance data from ichthyoplankton surveys and to preliminary estimates of seasonal egg productions. The study revealed significant interannual differences in the intensity of sprat egg cannibalism with considerable predation in 1990 to 1992 (> 15 % of the egg abundance during peak spawning and >60% of the seasonal production) and a reduction in most recent years (<16% of the corresponding abundance and production). As a possible reason for these differences a combination of changes in the vertical overlap of predator/prey and variability in the food environment were identified. Shortcomings of the applied methods and the possible impact of cannibalism on the reproductive success and population development of sprat m the Central Baltic Sea are discussed.

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Section: Discussionmentioning

confidence: 95%

Egg cannibalism in Baltic sprat Sprattus sprattus

Köster¹,

Möllmann²

2000

Mar. Ecol. Prog. Ser.

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“…Temperatures at the depth of the centre of mass of eggs were utilised for the estimation of developmental period. These were obtained from CTD (conductivity-temperaturedepth) casts performed concurrently with the vertically resolving ichthyoplankton sampling (Wieland and Jarre-Teichmann 1997). Finally, daily egg production rates were calculated by dividing the stage-specific abundance of live eggs by the development time of each egg stage.…”

Section: Observed Egg and Larval Standing Stocks And Productionmentioning

confidence: 99%

“…To model the vertical distribution of eggs, the observed distribution of the youngest egg stage (IA) obtained from vertically resolving ichthyoplankton sampling in 1986-1996 (Wieland and Jarre-Teichmann 1997) was examined in relation to water density profiles by fitting a parabolic function to the log relative distribution data (IA):…”

Section: Impact Of Oxygen Concentration On Egg Survivalmentioning

confidence: 99%

“…However, cod eggs become less buoyant after inflows when higher salinity occurs in the bottom water (Wieland and Jarre-Teichmann 1997). Hence, these hydrographic situations were modelled separately.…”

Section: Impact Of Oxygen Concentration On Egg Survivalmentioning

confidence: 99%

“…Köster and Möllmann (2000a) found that low oxygen concentration in the bottom water limited the vertical distribution of clupeids during the daylight feeding period, while the density regime determined the vertical distribution of cod eggs. Based on these observations, the average capture depth of the clupeids (Köster and Möllmann 2000a) and the average depth in which highest concentrations of cod eggs occurred (Wieland and Jarre-Teichmann 1997) were combined into an index of vertical predator-prey overlap determined for sampling dates in 1990-1996. Assuming an average residence depth of clupeids to correspond to the depth of occurrence of an oxygen concentration of 2 mL·L -1 , corrected by an offset of 3 m as observed in 1990-1996, allowed, in combination with observed (1986-1989) and modelled vertical distributions of cod eggs (1976)(1977)(1978)(1979)(1980)(1981)(1982)(1983)(1984)(1985), the calculation of predator-prey overlap indices for the entire time series.…”

Section: Predation On Cod Eggs By Clupeidsmentioning

confidence: 99%

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

Köster¹,

Hinrichsen²,

John³

et al. 2001

Can. J. Fish. Aquat. Sci.

101

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Abstract: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.Résumé : Nous cherchons à savoir si une approche axée sur les processus et basée sur des études de terrain, de laboratoire et de modélisation peut servir à développer un modèle stock-milieu-recrutement pour la morue franche (Gadus morhua) de la Baltique centrale. À la suite d'une analyse statistique exploratoire, des variables significatives qui influençaient la survie des premiers stades et qui variaient systématiquement d'une site de fraie à un autre ont été incorporées dans des modèles de stock-recrutement, d'abord pour les sites de fraie les plus importants et ensuite combinés pour toute la Baltique centrale. Les variables identifiées comprennent la production potentielle d'oeufs par le stock de géniteurs, les conditions abiotiques qui affectent la survie des oeufs, la prédation des oeufs par les clupéidés, le transport des larves et le cannibalisme. Les résultats indiquent que le recrutement durant la période 1976 à 1995 au site de fraie le plus important, le bassin de Bornholm, était en relation avec la production d'oeufs; cependant, d'autres facteurs significatifs affectaient la survie des oeufs (oxygénation, prédation) et, une fois incorporés, ils expliquaient 69% de la variation dans le recrutement du groupe 0. À d'autres sites de fraie, les conditions hydrographiques variables ne permettaient pas un développement normal et réussi des oeufs. Ainsi, des modèles relativement simples se sont avérés adéquats pour prédire le recrutement des morues du groupe 0 dans ces sites, ce qui laisse croire que des processus dominants abiotiques et biotiques peuvent être incorporés avec succès dans les modèles de recrutement.[Traduit par la Rédaction] Köster et al. 1556

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