Development of instrumental methods for accounting the spawning grounds area of herring in the Sea of Okhotsk

Abstract

Methods for accounting of herring spawning grounds area using consumer grade underwater robots and UAVs were worked out. Such devices are promising for use due to their relatively low cost, ease of deployment and application. Experimental procedures were carried out from May 11 to June 9 in the Kruglaya and Tungusskaya bays (the northern part of the Okhotsk Sea) during the period of herring spawning. With the help of underwater robots, spawning grounds should be surveyed by short point diving and short transects. Series of screenshots of bottom, recorded on a mobile device, could be georeferenced automatically. The work should be accompanied by the recording of tracks, station coordinates and other attribute data in a mobile geographic information system (GIS). Unmanned flights over spawning grounds must be carried out in the mode of automatic linear and polygon missions or manually. For the orthophotos production, the optimal height is 150 m with a forward overlap of images no less than 80% and a side overlap no less than 50% (no less than 20% in case of very good bottom visibility and survey conditions). During harsh survey conditions, zigzag flights over spawning grounds at a height of 50 m are preferred with shooting a series of photographs without intersection and no orthophotos production. The materials of underwater and unmanned surveys, integrated into the desktop GIS, provide high accuracy and efficiency in estimating the area of spawning grounds, the maximum degree of documentation and verifiability of the obtained materials.