Floating along buoyancy levels: Dispersal and survival of western Baltic fish eggs

Abstract

a b s t r a c tVertical distribution is an important feature of pelagic fish eggs and yolk sac larvae impacting their survival and dispersal, especially in heterogeneous and highly variable estuarine environments like the Baltic Sea. Egg densities determining the vertical distribution pattern were experimentally ascertained for cod (Gadus morhua), plaice (Pleuronectes platessa) and flounder (Platichthys flesus) from the western Baltic Sea. Plaice eggs floated at lower mean (±standard deviation) density range (1.0136 ± 0.0007 g cm À3 ) compared to cod (1.0146 ± 0.0009 g cm À3 ) and flounder eggs (1.0160 ± 0.0015 g cm À3 ), which floated on the highest density level. In flounder egg diameter was significantly related to egg density and in cod a weak correlation could be found between egg dry weight and density. All other relationships between female size, egg size, egg dry weight and egg density were not significant for any of the species. Available egg density data for Baltic Sea cod, plaice and flounder are summarized considering ICES subdivisions and stock management units. A hydrodynamic drift modeling approach was applied releasing drifters in the Belt Sea continuously from December to May, covering the species' spawning seasons. The model implemented experimentally derived egg density ranges and included ontogenetic egg density modifications for cod eggs, increasing egg density from a late egg development stage to first hatch. A drifter was removed from the model, i.e. considered dead, when its initially prescribed density value exceeded the density range available at the temporally resolved geographical positions along the drift trajectories. Highest survival occurred during releases in April and May but no cohorts survived if they were drifted east into the central Arkona Basin or the central Baltic Sea, irrespective of whether a major Baltic Inflow (1992/1993) or a stagnation-year (1987/1988) was simulated. The dispersal characteristics of the surviving yolk sac larvae of all three species reflected retention within the Belt Sea or northwards transport through the Great Belt into the Kattegat and partly into the Skagerrak. There was no successful transport to more eastern Baltic areas past a hypothetical line from the island of Moen (Denmark) to Kap Arkona on Rügen Island (Germany).

Modeling the effects of temperature on the survival and growth of North Sea cod (Gadus morhua) through the first year of life

“…To our knowledge, such research has not been conducted for North Sea cod. Based on the studies on egg buoyancy of cod dwelling elsewhere in the North Atlantic and Baltic, we concluded that cod eggs are positively buoyant and located the upper water layer (Kjesbu et al ., ; Nisslingl et al ., ; Petereit et al ., ). Most of the eggs are confined to the upper 20 m with strong winds or waves infrequently mixing eggs to the deeper layers (Sundby, ; Röhrs et al ., ).…”

Oxygen depletion in coastal seas and the effective spawning stock biomass of an exploited fish species

“…As obtained from field observations as well as from laboratory experiments for eastern Baltic cod, a minimum salinity level of 11 psu is required for neutral egg buoyancy, whereas eggs at lower salinities sink to the bottom and die. At the same time, a minimum oxygen level of 2 ml l −1 and temperatures above 1.5°C are required for eggs to develop successfully [17,18,31]. …”

Characteristics of juvenile survivors reveal spatio-temporal differences in early life stage survival of Baltic cod

“…A detailed description of these model runs can be found in Hinrichsen et al (2003b). A recent study by Petereit et al (2014), using the same hydrodynamic model, did explicitly address the issue of horizontal diffusion and its influence on final drift destinations in the Baltic Sea. Model sensitivity experiments to evaluate the influence of horizontal diffusion on the final distribution of drifters did not reveal any significant deviations from the results of a reference run (i.e.…”