Drivers, dynamics and management of Eastern Baltic cod (Gadus morhua) reproduction habitat

• Main Author: von Dewitz, Burkhard
• Other Authors: Reusch, Thorsten B. H., Gröger, Joachim
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2018
• Subjects: thesis; ddc:570; Baltic Sea; Eastern Baltic cod; fisheries management; environmental indicators; spawning habitat; oceanographic modeling; Gadus morhua
• Online Access: https://nbn-resolving.org/urn:nbn:de:gbv:8-diss-239412; https://macau.uni-kiel.de/receive/diss_mods_00023941; https://macau.uni-kiel.de/servlets/MCRFileNodeServlet/dissertation_derivate_00007907/PhD_Thesis_Burkhard_von_Dewitz.pdf

The overall aim of my thesis was to improve our understanding of environmental drivers causing the dynamics of the Eastern Baltic cod reproduction habitat and to assess their relevance for a possible application in the sustainable stock management. A novel approach to map the reproductive habitat of Eastern Baltic cod, the Buoyancy Depending Reproductive Layers (BDRL), was developed and used to propose an alternative stock indicator, the effective Spawning Stock Biomass (eSSB). The eSSB was found to improve the fit of a recruitment model compared to the model using the conventional Spawning Stock Biomass. Oxygen depletion was also negatively impacting the available size of nursery areas for juveniles. The mechanism was able to partly explain the observed decline of the condition of juveniles in the nursery areas, because a high population density in the remaining habitat could increase the impact of density depending effects. Furthermore, by the application of the novel approach of BDRLs the spawning habitat was shown to be sensitive to eutrophication and that this sensitivity is strongly depending on the size of the female spawner using the habitat. As predicted, the BDRL approach was superior to the “classic” approach, the Reproductive Volume (RV) because it was more sensitive to environmental change, able to incorporate stock structure, was not overestimating the spawning habitat in the eastern spawning areas and could provide estimates of other stressors depending on the female spawner size. Due to a permanently installed measurement platform in the Arkona Basin, the new methodology could be used to establish a new environmental indicator on the spawning habitat conditions. It was recommended to be used in future stock assessments. Das Ziel dieser Arbeit war unser Verständnis der treibenden Umweltparameter dieser Entwicklung und ihrer Dynamic zu verbessern und sie auf eine mögliche Nutzung im Zusammenhang mit einem nachhaltigen Management des Bestandes zu überprüfen. Entwickelt wurde eine neue Methode die ...