Aerial photovisual surveys using UAVs to assess sockeye salmon stock abundance in the basin of Azabachye Lake

Abstract

Experience of the use of different unmanned aerial vehicles (UAVs) in the aerial assessment of sockeye salmon Oncorhynchus nerka spawners in the basin of the Azabachye Lake, Kamchatka Territory, is described in this article. The purpose of the research was to assess efficiency of remote monitoring in case of changing water transparency and spatial disunity of spawning grounds for early and late spawning sockeye salmon morphs. Assessment of the early morph was carried out in two stages: in late June to assess sockeye salmon aggregations in the outlet zones of small tributaries and in mid July to assess them in major spawning grounds of the Bushuyka, large tributary of the lake, in terms of optimal water transparency. Assessment of the late morph was carries out in the third decade of August in the waters of the lake and in the main body of the Bushuyka. Obtained results were compared to results of hydroacoustic monitoring. The analysis has demonstrated a high consistency of the methods used and confirmed practical suitability of the UAVs to assess spawning aggregations accurately even in case of hard hydrological conditions. The use technology has demonstrated high efficiency, representativeness, and potential for further implementation in the Pacific salmon monitoring system.