- Rapid response to evaluate the presence of amphibian chytrid fungus Batrachochytrium dendrobatidis and ranavirus in wild amphibian populations in Madagascar.
- Mathematical Models in Population Biology and Epidemiology | Fred Brauer | Springer
- Publications - Helmholtz-Zentrum für Umweltforschung UFZ
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- The concept of equilibrium states of populations and ecosystems has been confronted with that of ever-changing states of biotic entities, and the role of environmental vs.
Professor N. Abstract The relative importance of exploitation rate and environmental variability in generating fluctuations of harvested populations is a key issue in academic ecology as well as population management.
We studied how the eastern Baltic cod Gadus morhua is affected by fishing and environmental variation by using a newly developed single species state-space model. Survey data and auxiliary environmental data were used to estimate the model parameters. The model was then used to predict future development of the eastern Baltic cod under different fishing mortalities and abiotic conditions.
Abiotic condition was represented by an index: sustainability in single species population models volume which is the volume of water suitable in terms of salinity and oxygen content for the successful development of the early life stages of Baltic cod. The model included direct density dependence, fishing, and a lagged effect of reproductive volume.
At a finer search grid, differences, if also minor ones, would probably have occurred in all scenarios. A fishing strategy opting for maximum yields in tonnes combined will thus plea for slightly higher efforts, resulting in higher catches of plaice but overfishing of sole, while the opposite will be the case for strategies aiming for high revenues from landings. Discussion This study explores the sensitivity of msMSY fishing strategies and yields to projected ecological changes in a food-web model of the southern North Sea.
Single party steinfurt analysis showed that fishing rate is approximately three times more important than reproductive volume in explaining the population dynamics.
Furthermore, our model suggests either under- or over-compensatory dynamics depending on the reproductive volume and long term catch levels.
Single species population discrete time model and logistic difference equation
It follows that fishing can either reduce or increase temporal oscillations of the cod stock depending on whether the dynamics is over- or undercompensatory, respectively. The sustainable level of fishing rate is however dependent on reproductive volume. Our model predicts a dual role of fishing rate, stabilizing when reproductive volume is high and destabilizing when it is low.
Exploitation rate may therefore increase or decrease the risk of the population of cod dropping below a given biomass reference point depending on the environmental conditions, which has practical implications for fisheries management.