Spatial and temporal heterogeneity of the cod spawning environment in the Bornholm Basin, Baltic Sea

The present study quantifies the spatial heterogeneity of the environmental conditions associated with successful spawning by cod Gadus morhua in the Bornholm Basin. Quarterly means from 1989 to 2003 of the thickness of reproductive volume that enabled egg survival indicate that most favourable spawning conditions were located in the central area, inside the 80 m isobath. On average, spatial patterns were similar in the second and third quarters, but with overall lower thicknesses of reproductive volume and less horizontal extension of conditions suitable for egg survival in the third quarter. The observed basin-wide variation in thickness of reproductive volume and oxygen content inside this volume can result in marked horizontal differences in oxygen-related egg mortality, especially during stagnation years. The spawning habitat selected by adult Baltic cod in the Bornholm Basin was characterised by comparing data on egg abundance with environmental variables measured concurrently with egg collection. A clear preference for spawning at locations in the deep basin is evident after both inflow events, as well as for stagnation periods. In consequence, the closed area for fishing implemented in the Bornholm Basin during the main spawning periods from 1995 to 2003, although located in the northern centre of the basin, did not necessarily ensure undisturbed spawning in stagnation years

Energetic particle influence on the Earth's atmosphere

This manuscript gives an up-to-date and comprehensive overview of the effects of energetic particle precipitation (EPP) onto the whole atmosphere, from the lower thermosphere/mesosphere through the stratosphere and troposphere, to the surface. The paper summarizes the different sources and energies of particles, principally galactic cosmic rays (GCRs), solar energetic particles (SEPs) and energetic electron precipitation (EEP). All the proposed mechanisms by which EPP can affect the atmosphere are discussed, including chemical changes in the upper atmosphere and lower thermosphere, chemistry-dynamics feedbacks, the global electric circuit and cloud formation. The role of energetic particles in Earth’s atmosphere is a multi-disciplinary problem that requires expertise from a range of scientific backgrounds. To assist with this synergy, summary tables are provided, which are intended to evaluate the level of current knowledge of the effects of energetic particles on processes in the entire atmosphere

Environmental factors influencing larval sprat Sprattus sprattus feeding during spawning time in the Baltic Sea

The management of Baltic sprat is challenged by highly variable recruitment success and hence large stock fluctuations. Recent studies have identified the larval and early juvenile life stages to be critical for the survival rate of a sprat year class. Although prey abundance was found to be linked to larval survival success, an analysis identifying the functional relationship and relative importance of other environmental factors is still missing. Sprat larval feeding was investigated in 2002 during three cruises, covering the main spawning time in the Bornholm Basin, Baltic Sea. The aim of the study was to identify the key environmental factors determining the feeding success of larval sprat taking their potential interactions explicitly into account. An extension of generalized additive models (GAMs) was adopted that allows the inclusion of interaction terms in a non-parametric regression model. The final model of sprat larval feeding success explained ∼80% of the variance in the data and was based on the following environmental factors: bottom depth, cubed wind speed as proxy for small-scale turbulence rates, degree of cloudiness as proxy for light conditions and prey density in combination with a feeding period–cloudiness interaction term. Our study demonstrates that the feeding success of sprat larvae in the Baltic Sea is controlled by a number of simultaneously acting key environmental factor

Recruitment variability in Baltic Sea sprat (Sprattus sprattus)is tightly coupled to temperature and transport patterns affecting the larval and early juvenile stages

Recruitment patterns of Baltic Sea sprat (Sprattus sprattus) were correlated to time series of (i) month- and depth-specific temperature conditions and (ii) larval drift patterns inferred from long-term Lagrangian particle simulations. From the latter, we derived an index that likely reflected the variable degree of annual larval transport from the central, deep spawning basins to the shallow coastal areas of the Baltic Sea. The drift index was significantly (P < 0.001) correlated to sprat recruitment success and explained, together with sprat spawning stock biomass, 82% of the overall variability between 1979 and 2003. Years of strong larval displacement towards southern and eastern Baltic coasts corresponded to relative recruitment failure, while years of retention within the deep basins were associated with relative recruitment success. The strongest correlation between temperature and recruitment occurred during August in surface waters, explaining 73% of the overall variability. Together, the two approaches advocate that new year classes of Baltic sprat are predominantly composed of individuals born late in the season and are determined in strength mainly by processes acting during the late larval and early juvenile stages. However, prior to be included in recruitment predictions, the biological mechanisms underlying these strong correlations may need to be better resolve

Modelling the influences of atmospheric forcing conditions on Baltic cod early life stages: distribution and drift

Retention or dispersion of larvae from the spawning ground has been identified as one of the key processes influencing recruitment success in fish stocks. An exercise combining 3-D hydrodynamic model simulations and field data on spatial distributions of juvenile Baltic cod was utilised to investigate the potential drift of larvae from the centre of main spawning effort in the Bornholm Basin, Baltic Sea. In the simulations cod larvae were represented as Lagrangian drifters. Habitats in which larvae and juvenile cod potentially dwell and where juveniles settle were identified to ascertain the importance of predicting transport. The transport of Baltic cod larvae was investigated by detailed drift model simulations for the years 1986 to 1999. The results yielded a clear dependency on wind-induced drift of larval cod, which is mainly controlled by the local atmospheric conditions over the Baltic Sea. Seasonally averaged distributions of drifters were compared with actual distributions of 0-group cod, as determined from bottom and pelagic trawl surveys conducted in autumn of the years 1993 to 2000 in and around the Bornholm Basin. The results suggest that juveniles caught in different areas can be assigned to different times of the spawning season. Because of seasonal differences in the circulation patterns, the southern coastal environment is on average most important for early and late spawners, whereas larvae hatching in mid-summer were on average transported towards the north or to a higher degree remained in the spawning ground