Analyse des Fluchtverhaltens von Fischen auf Schiffsgeräusche mit hydroakustischen Methoden

Investigations on the avoidance reactions of pelagic schooling fish (herring and sprat) released by an approaching fishery vessel were carried out during the 378th cruise of FRC "Solea" from 25 September to 3 October 1995 in the Arkona Sea, southern Baltic. An echosounder system EK 500/BI500 with a 38 kHz transducer mounted on a towed body as weIl as a 120 kHz hull mounted transducer were used. Fish densities were measured synchronously as well as under the ship as at a laterally distances from the ship by the transducer of the towed body. By these means the variation of fish densities up to a certain distance from the ship is possible. The advantage of using an echo integrating system for these measurements is, that it works also for not schooling fish and under conditions where schooling fish disperse (e.g. at night).

Ergebnisse weiterer Versuche mit Schersegeln

Als Schersegel werden hydrodynamische Auftriebsvorrichtungen am Kopftau von Schleppnetzen bezeichnet, die in ihrer Wirkungsweise einem Höhenscherbrett entsprechen. Im Gegensatz zu der starren Konstruktion eines Höhenscherbretts aus Holz oder Aluminium bestehen Schersegel jedoch aus flexiblem Material, im allgemeinen beidseitig kunststoffbeschichtetem Gewebe.

The role of infusoria and bacteria as food for Cyclopoida in Rybinsk Reservoir [Translation from: Trudy Instituta Biologii Vnutrennykh Vodnany 22(25), 37-42, 1971]

Despite the fact that it is a long time sinc e the methods of collection and quantitative estimatio n of protozoa were worked out data on the abundance of these animals in freshwaters are not very numerous. Nevertheless, Infusoria and Rhizopoda at high densities are widespread in the water and sediments of lakes and reservoirs. In order to find ou t the importance of infusoria as a food source for cyclopoids we carried out experimental investigations using C14. For this three species of cyclopoids, widely distributed in open regions of Rybinsk reservoir were selected: Cyclops vicinus, Mesocyclops oithonoides and Kesocyclops leuckarti. The data presented give evidence that the species investigated are able as predators to consume infusorian plankton arid bacteria in the form of flocs or small clumps of detritus.

A tool for better management of water quality during periods of algal blooms: the case of the River Oise

Like other rivers in the Paris area, the Oise is subject to important seasonal algal blooms. This eutrophication generates notable problems for the production of drinking-water from a treatment plant on the river at Méry. A mathematical model has been developed to simulate variation in water quality in a pre-treatment storage basin, and another model is currently being adapted to model the River Oise. Integration of the two models should provide a comprehensive tool for predicting variations of phytoplankton and water-quality parameters associated with algal blooms. This will be a decision-aid for optimizing control of the treatment process for providing potable water.