Baltic cod reproduction in the Gotland Basin: annual variability and possible causes

Baltic cod spawning takes place in the deep basins and reproduction success is mainly related to environmental conditions (salinity and oxygen regimes, i.e. the 'reproduction volume'). Due to the Baltic Sea heterogeneity, cod reproduction success in the Southem and Centrat Baltic spawning grounds can differ significantly. Recent oceanographic changes i.e. decrease of water exchange and stagnation, as weil as a strong reduction of spawning stock caused the diminishing of the reproduction potential of the Gotland spawning grounds. The Gotland spawning grounds belong to four main cod spawning sites in the Baltic and historical analyses revealed that abundant generations of Baltic cod were produced when successful cod reproduction took place also in the Gotland Basin. Analyses of revised reproduction volume estimates for the Gotland Basin taking into account the spatial structure of hydrology in the basin during stagnation and aeration periods reveals high seasonal and inter-annual variability. To describe changes of abundance and distribution of the spawning stock and the recruits in relation to hydrographic conditions, results from trawl surveys carried out in 1975-1998 in the Gotland Deep are analyzed. In this analysis, the reproduction volume is used as a proxy for the environmental conditions

Insights into the link between bulk and surface properties of solid oxide fuel cell cathode materials

Solid oxide fuel cells (SOFCs) possess the potential for efficient conversion of chemical energy to electrical energy with minimal production of pollutants. Development of intermediate temperature solid oxide fuel cells (IT-SOFCs) requires the development of more active electrode materials due to the high activation energies associated with oxygen dissociation and incorporation. Both the surface activities and bulk conductivities for oxygen dissociation and transport have been measured for a wide variety of cathode materials utilizing isotopic depth profiling and thermogravimetric analysis techniques, with a correlation found between these values. As discussed within however, these techniques can be misleading for a variety of reasons. Consequently, a combination of bulk and surface measurement techniques including neutron powder diffraction, isotopic oxygen pulsing, as well as surface composition measurements were performed for a range of perovskite-related materials to define the nature of this relationship between surface and bulk properties.It was found that the link between surface reaction rates and bulk conductivity is caused by a difficulty in measuring the actual “surface” reaction rate, as several materials with notably similar surface compositions exhibited significantly different reaction rates. Similarly, these surface reaction rates were directly linked to the bulk structure through an oxygen vacancy hopping mechanism. As such, we conclude that the measurement of surface reaction rates is limited by an incorporation step which has oxygen on the surface of the material migrate into the bulk structure rather than any actual limitation of oxygen dissociation on the surface or bulk oxygen transport

Female ovarian abnormalities and reproductive failure of autumn-spawning herring (Clupea harengus membras) in the Baltic Sea

Fecundity and reproductive potential are important factors to be considered in evaluating trajectories and demographic predictions of fish populations. Therefore, characterizing the nature and quantifying the extent of any reproductive failure should be considered in fisheries studies. Here, we describe morphological changes in developed ovaries of autumn-spawning herring (Clupea harengus membras) caught in the northern Baltic Sea and evaluate the magnitude of this phenomenon during 3 consecutive years. Visibly, abnormal ovaries were histologically characterized by irregular-shaped oocytes in a vitellogenic or final maturation stage with coagulative necrosis and liquefaction of the yolk sphere, degraded follicle membranes, and fibrinous adhesion among oocytes. Such degeneration is presumed to cause complete infertility in the fish. The frequency of fish with abnormal ovaries varied annually between 10 and 15% among all females sampled. However, specific sampling events showed up to 90% females with abnormal gonads. The specific cause of this abnormality remains unknown; however, prevalence was associated with unfavourable environmental conditions encountered before spawning. Thus, ovarian abnormality was positively related to water temperatures, with the highest level found at ≥15°C and negatively related to the frequency of strong winds. The frequency of occurrence of abnormal gonads decreased with the progression of spawning from August to October. The observed abnormality and associated spawning failure will negatively affect the realized fecundity of autumn herring in the Baltic Sea and may act as a limiting factor for recovery of the stock, which has experienced profound depression during the last three decades