Discriminating the diel vertical migration of fish andChaoborus flavicanslarvae in a lake using a dual-frequency echo sounder

Abstract

-The diel vertical migration of fish and larvae of the phantom midge Chaoborus flavicans was studied using a combined 38 and 200 kHz echo sounder. Multi-mesh gill net was used to sample fish, and a Schindler-Patalas trap to sample Chaoborus. Oxygen and temperature profiles were also recorded. At 38 kHz, only fish were detected, without considerable interference from Chaoborus echoes. At 200 kHz, both fish and Chaoborus were detected and echoes from Chaoborus almost completely masked all fish echoes at night. During the day, Chaoborus remained hidden in an oxygen-poor refuge near the bottom. Tracks of fish diving into the Chaoborus refuge were observed on several occasions. At the onset of dusk, Chaoborus started to rise and by the time it was dark they were occupying the whole water column. Fish were found in patches in midwater during the day. In the dark, the fish were dispersed throughout the water column. Results suggest that a dual-frequency approach can be used to discriminate between fish and Chaoborus and to provide a rapid method for their selective monitoring.

Experimental evidence of a low‐oxygen refuge for large zooplankton

“…Yellow perch (Perca flavescences) in Lake Erie avoid water with oxygen concentrations , 2 mg L 21 , but occasionally they 'dive' into hypoxic waters to feed on bottom fauna (Roberts et al 2009). Using hydroacoustic equipment that discriminated between fish and Chaoborus larvae, Knudsen and Larsson (2009) observed individual fish penetrating the hypolimnion to feed. However, for crustacean zooplankton, the risk of being eaten is much smaller in hypoxic than in oxic waters if fish spend only a fraction of their time foraging in the refuge.…”

Implementing and Innovating Marine Monitoring Approaches for Assessing Marine Environmental Status

“…Multiple frequency scientific echosounders with split-beams and resulting echo-trace analysis (using frequency responses) can provide information on the sizes of animals, thus allowing some distinctions to be made. Despite the fact that the underwater acoustic instruments do not allow species classification (Knudsen and Larsson, 2009), they could be useful to gain information on pelagic and semi-demersal species as well as on zooplankton assemblages (Trenkel et al, 2011; Table 2). The Acoustic Complexity Index (ACI) coupled with a software dedicated to soundscape analysis can be used to elaborate collected acoustic files, in order to track the various biological signals, their daily and nightly dynamics and distinguish them from noise pollution.…”

A global review of the spatial, taxonomic, and temporal scope of freshwater fisheries hydroacoustics research

“…Vertical migrations in coregonids (Gjelland and Bohn 2004;Knudsen and Gjelland 2004) and vendace (Hamrin 1986) have been well studied in Scandinavia. Other studies have compared fish echo traces with those of pelagic invertebrates (Knudsen and Larsson 2009;Knudsen et al 2006), studied factors affecting D r a f t recruitment variability (Axenrot and Degerman 2016), and have investigated effects of introduced species (Brabrand and Faafeng 1993) and climate change (Nyberg et al 2001) on aquatic systems. (Lilja et al 2000) studied TS of Atlantic salmon, brown trout (Salmo trutta), whitefish and pike (Esox lucius) in Finland (see Table 1), where extensive work has been done on fish abundance estimates (e.g.…”