Simulierte Auswirkungen des mehrjährigen Bewirtschaftungsplans für die Dorschfischerei in der westlichen Ostsee und die Möglichkeit einer technischen Alternative

The cod stock in the Western Baltic Sea is assessed to be overfished regarding the definitions of the UN World Summit on Sustainable Development at Johannesburg in 2002. Thus, the European Fisheries Council enforced a multi-annual management plan in 2007. Our medium term simulations over the future 10 years assume similar stock productivity as compared with the past four decades and indicate that the goals of the management plan can be achieved through TAC and consistent effort regulations. Taking account of the uncertainty in the recruitment patterns, the target average fishing mortality of age groups 3 – 6 years of F = 0.6 per year as defined in the management plan is indicated to exceed sustainable levels consistent with high long term yields and low risk of depletion. The stipulated constraint of the annual TAC variations of ±15% will dominate future fisheries management and implies a high recovery potential of the stock through continued reductions in fishing mortality. The scientific assessment of sustainable levels of exploitation and consideration in the plan is strongly advised, taking account of uncertainties attributed to environmental and biological effects. We recommend our study to be complemented with economic impact assessments including effects on by-catch species, which have been disregarded in this study. It is further demonstrated, that the goals of the management plan can alternatively be achieved by mesh size adaptations. An alternative technical option of mesh size increases to realize the required reductions in fishing mortality provides avoidance of discards of undersized fish after a few years by means of improved selectivity, another important element of the Common Fisheries Policy. However, it is emphasized that technical regulations since 1990 failed to affect the by-catch and discards of juvenile cod. In any way, the meaningful implementation of the multiannual management plan through stringent control and enforcement appears critical.

Decision support systems optimising effluent release in sub tropical estuarine environment - An Australian case study

Gold Coast Water is responsible for the management of the water and wastewater assets of the City of the Gold Coast on Australia’s east coast. Treated wastewater is released at the Gold Coast Seaway on an outgoing tide in order for the plume to be dispersed before the tide changes and renters the Broadwater estuary. Rapid population growth over the past decade has placed increasing demands on the receiving waters for the release of the City’s effluent. The Seaway SmartRelease Project is designed to optimise the release of the effluent from the City’s main wastewater treatment plant in order to minimise the impact of the estuarine water quality and maximise the cost efficiency of pumping. In order to do this an optimisation study that involves water quality monitoring, numerical modelling and a web based decision support system was conducted. An intensive monitoring campaign provided information on water levels, currents, winds, waves, nutrients and bacterial levels within the Broadwater. These data were then used to calibrate and verify numerical models using the MIKE by DHI suite of software. The decision support system then collects continually measured data such as water levels, interacts with the WWTP SCADA system, runs the models in forecast mode and provides the optimal time window to release the required amount of effluent from the WWTP. The City’s increasing population means that the length of time available for releasing the water with minimal impact may be exceeded within 5 years. Optimising the release of the treated water through monitoring, modelling and a decision support system has been an effective way of demonstrating the limited environmental impact of the expected short term increase in effluent disposal procedures. (PDF contains 5 pages)