Circulation of Knowledge in the Baltic Sea Region:

Integrated ecosystem impacts of climate change and eutrophication on main Baltic fishery resources

“… First of all, our model has no oxygen depleted zones in the deep offshore basins where cod spawning occurs, which is in contradiction with current observations (Carstensen and Conley, 2019;Hansson et al, 2019) and which has to be adjusted accordingly. In addition, even though oxygen layers from SCOBI were available, we were not able to use them because if we would overlay those to the already existing Baltic Atlantis oxygen field, this would give inconsistencies and lack of mass conservation.…”

“…Oxygen levels have been critically low for several decades in the deeper basins of the Baltic Sea, e.g. the Bornholm and Gotland Basins (Hansson et al, 2019) and it is predicted that the areal extent and volume of hypoxia will further increase because of climate change and nutrient supply (Saraiva et al, 2019a). We have, in the present study, shown that this increase probably will have a negative impact on the cod population with a decrease in its main food source leading to a lower weight of juvenile cod, as is also shown in other studies (e.g.…”

“…Finally, climate change pressure is high, because many species in the Baltic Sea already live at the edge of their environmental tolerance levels (Snoeijs-Leijonmalm et al, 2017). These pressures have individually been investigated in many studies under current climate conditions such as: the long history of eutrophication (Andersen et al, 2017;Heiskanen et al, 2019;Murray et al, 2019) and hypoxia (Almroth-rosell et al, In prep;Hansson et al, 2019), the impact of hypoxia on consumption rates of pelagic commercial fishes (Teschner et al, 2010), as well as the impact of the fisheries on the food web (e.g. Harvey et al, 2003).…”

Into the wild: coupling otolith and archival tag records to test assumptions underpinning otolith chemistry applications in wild fish

“…Salinity conditions are inflow dependent, but the halocline depth has remained fairly constant across multiple decades (Carstensen et al, 2014). As a result of this stable salinity stratification and decades of eutrophication, the extent of hypoxic areas has been spreading as a persistent layer in the deeper basins (Helcom, 2009;Viktorsson, 2018;Hansson et al, 2019;Naumann et al, 2020). Many shallower areas within the Baltic Sea, with restricted exchange of bottom water due to complex bottom topography, also suffer from seasonal periods of hypoxia during summer (Conley et al, 2011;Carstensen and Conley, 2019).…”