Hydro-acoustic methods as a practical tool for cartography of seagrass beds

Cartography of seagrass beds is very important for management and conservation of sound littoral ecosystems and sustainable fisheries in the coastal waters. The cartographical methods to map spatial distribution of seagrass beds are reviewed. They are classified into two categories. One is a direct method by visual observation and the other is an indirect method using a remote sensing apparatus. Indirect methods are divided into optical or hydro-acoustic methods. Indirect methods require sea truth by direct methods. Optical methods are image analysis of aerial photography or satellite imagery. They are effective for mapping broad areas but limited to shallow waters due to light attenuation in waters. Hydro-acoustic methods such as an echosounder and a side scan sonar have no limitation of turbidity. The echosounder is practical to map vertically density and height distributions of seagrass beds. The side scan sonar and multi-beam sonar are appropriate for mapping broad horizontal distributions. Coupling of several indirect mapping methods is more useful than using only one method

Video analysis of fish schooling behavior in finite space using a mathematical model

The schooling behavior of the fish Parapristipoma trilineatum (chicken grunt) was examined for a range of school sizes in a water tank containing a central columnar structure using a mathematical model of fish schooling behavior that was modified from that of Sannomiya and Matuda. The two-dimensional motion of individuals was captured on digital video over about 10 min, and these time-series data were used to tune the model to the experimental conditions. The model parameters were then used to evaluate schooling behavior quantitatively. Comparing force magnitudes between experimental conditions revealed that propulsive force was less in a tank without the central structure than in a tank with the central structure, under all conditions tested. These results indicate that the school was less active under unobstructed conditions. Propulsive force also decreased with increasing school size. Attractive and repulsive forces of the walls were dominant for smaller school sizes; the attractive and repulsive forces of the structure were significant only for the largest school tested (25 individuals). Thus, changes in behavioral patterns caused by the number of individuals or the presence of structures can be expressed using the mathematical model

網地の形状と運動に関する数値計算モデルの妥当性と可視化について

網漁具の水中での形状や運動を推定できる数値シミュレーション手法を開発するために，本報では前報で示された計算用モデルの妥当性を検証する。実験では定常流中に3種類の長方形の平面網地を設置し，流速を変化させながら網形状と網糸に作用する荷重を計測した。網地形状の計算結果はどのケースでも実物と非常に良く一致した。平面網地上辺に作用する荷重は計算結果と良い一致を示した。網糸張力の分布状況についても，実験結果と概ね一致した。これらの結果は本計算モデルが網漁具の形状や運動を推定するのに十分有効であることを示す。The aim of the present study was to develop a numerical calculation method to simulate the three-dimensional dynamic behavior of fishing nets. In a previous study, we presented a formulation to calculate net configurations. In this method, fishing nets were modeled as a group of lumped mass points interconnected with springs that have no mass. To verify the validity of calculation results using a computational model, we performed the flume tank experiments with a rectangular net and compared results with those of the numerical simulation of experiments. Using our method, numerical calculations for a rectangular net in a steady flow can provide accurate results. The calculated load and tension force distribution of the flat net were generally in accordance with the results of the flume tank experiments. This study shows that our method is valid for the simulation of fishing nets; furthermore, we have resolved earlier problems that were associated with this model

Hydro-acoustic methods as a practical tool for cartography of seagrass beds

Cartography of seagrass beds is very important for management and conservation of sound littoral ecosystems and sustainable fisheries in the coastal waters. The cartographical methods to map spatial distribution of seagrass beds are reviewed. They are classified into two categories. One is a direct method by visual observation and the other is an indirect method using a remote sensing apparatus. Indirect methods are divided into optical or hydro-acoustic methods. Indirect methods require sea truth by direct methods. Optical methods are image analysis of aerial photography or satellite imagery. They are effective for mapping broad areas but limited to shallow waters due to light attenuation in waters. Hydro-acoustic methods such as an echosounder and a side scan sonar have no limitation of turbidity. The echosounder is practical to map vertically density and height distributions of seagrass beds. The side scan sonar and multi-beam sonar are appropriate for mapping broad horizontal distributions. Coupling of several indirect mapping methods is more useful than using only one method