Diver-towed global positioning systems (GPS) handhelds have been used for a few years in underwater monitoring studies. We modeled the accuracy of this method using the software KABKURR originally developed by the University of Rostock for fishing and marine engineering. Additionally, three field experiments were conducted to estimate the precision of the method and apply it in the field: (1) an experiment of underwater transects from 5 to 35 m in the Southern Chile fjord region, (2) a transect from 5 to 30 m under extreme climatic conditions in the Antarctic, and (3) an underwater tracking experiment at Lake Ranco, Southern Chile. The coiled cable length in relation to water depth is the main error source besides the signal quality of the GPS under calm weather conditions. The forces used in the model resulted in a displacement of 2.3 m in a depth of 5 m, 3.2 m at a 10-m depth, 4.6 m in a 20-m depth, 5.5 m at a 30-m depth, and 6.8 m in a 40-m depth, when only an additional 0.5 m cable extension was used compared to the water depth. The GPS buoy requires good buoyancy in order to keep its position at the water surface when the diver is trying to minimize any additional cable extension error. The diver has to apply a tensile force for shortening the cable length at the lower cable end. Repeated diving along transect lines from 5 to 35 m resulted only in small deviations independent of water depth indicating the precision of the method for monitoring studies. Routing of given reference points with a Garmin 76CSx handheld placed in an underwater housing resulted in mean deviances less than 6 m at a water depth of 10 m. Thus, we can confirm that diver-towed GPS handhelds give promising results when used for underwater research in shallow water and open a wide field of applicability, but no submeter accuracy is possible due to the different error sources.

From the point of view of mechanics, trawls are considered as extremely flexible and partly extensible rope and net structures which are exposed to flow. Form and loads of such gears mainly depend on the corresponding velocity of inflow and also on the so-called rigging elements that are required for the horizontal and vertical spreading of the fishing gear. At the same time the fishing gear is acting on the surrounding fluid. These reactions can on the one hand lead to unsteady states in the fishing gear. On the other hand changes of pressure and velocity can be detected by the fish and can possibly influence the selectivity of the fishing gear. This lecture is focused on the presentation of special numerical and experimental methods both for calculating large net systems and for analysing the reactions of the structure to the fluid.

Fishing technic CALCULATION OF FISmNG GEAR AS DISCRETE MODELS ZASTOSOWANIE MODELU DYSKRETNEGO W OBLICZENIACH NARZ�DZI RYBACKICH Sektion Schlffstechnik W ilhelm-Pieck-Universi. tet-RostockThe paper deals with a new calcttlation method of discretizing complicated line system and netting of fishing gear, that makes possible a successive approximation of assesed initial values to the true solution.

Time lapse photography with two different camera systems for in situ observation of the bivalve Diplodon chilensis (Gray, 1828) in a southern Chilean lakeFotografía en lapso de tiempo con dos sistemas de cámaras diferentes para la observación in situ del bivalvo Diplodon chilensis (Gray, 1828) en un lago del sur de Chile ABSTRACT We compared the validity of two low cost camera systems to analyze the fi ltration activity of Diplodon chilensis (Gray, 1828), the most common freshwater bivalve in southern Chile, by using time lapse photography. One camera system (Nikon D300) was connected with an external fl ash, whereas the other system (GoPro Hero 3+) contained a permanent video light source. Size change of the exhalant siphon area (ESA) of Diplodon individuals was used to track activity changes over time. The siphon of D. chilensis was completely closed for 3.4 % ± 5.2 % (mean ± SD) of the recording time and it shows a nearly completely opened siphon for 42.7 % ± 22.9 % of the recording time. The mean siphon opening was 68.3 % ± 26.5 % of its potential opening area. Although a red fi lter was placed in front of the video light source, the mobile fauna, especially Aegla abtao (Schmitt, 1942) and unidentifi ed small fi shes were highly attracted by the permanent light. We conclude that both low cost cameras are very suitable for in situ time lapse observation of freshwater clams since both deliver good image quality. However, special attention should be given to the light source since permanent light attracts animals including predators which might change fi ltration activity of D. chilensis. KEYWORDS: camera system comparison, Diplodon chilensis, exhalant siphon area, time lapse photography. RESUMENComparamos la validez de dos sistemas de cámara de bajo costo para analizar la actividad de fi ltración de Diplodon chilensis (Gray, 1828), el bivalvo de agua dulce más común en el Sur de Chile, usando fotografía de lapso de tiempo. Un sistema de cámara (Nikon D300) se conectó con un fl ash externo, mientras que el otro sistema (GoPro Hero 3+) contenía una fuente de luz de vídeo permanente. El sifón de D. chilensis fue completamente cerrado por 3.4 % ± 5.2 % (media ± desviación estándar) del tiempo de grabación y muestra un sifón casi completamente abierto durante 42.7 % ± 22.9 % del tiempo de grabación. La apertura media del sifón fue de 68.3 % ± 26.5 % de su área de apertura potencial. Aunque un fi ltro rojo se colocó frente a la fuente de luz de vídeo, la fauna móvil, especialmente Aegla abtao (Schmitt, 1942) y los peces pequeños no identifi cados, fueron fuertemente atraídos por la luz permanente. Concluimos que ambas cámaras son adecuadas para la observación in situ de fotografía en lapso de tiempo de las almejas de agua dulce, ya que ambas ofrecen una buena calidad de imagen. Sin embargo, se debe prestar especial atención a la fuente de luz, ya que la luz permanente atrae a los animales, incluidos los depredadores, que podrían cambiar la actividad de fi ltración de D. chilensis. PALABRAS CLAVE: área de sifón e...