New Approaches to Assess Freshwater Fish Abundance and Activity: Linking Hydroacoustic and Telemetry Methods

The determination of fish abundance has long been a cornerstone of fisheries science.  Annual abundance estimation of large- and small-bodied fish species traditionally requires a substantial investment in time and resources.  Thus, methods, such as hydroacoustics are of interest because they present a cost-effective way to passively assess fish populations, including evaluation of fish abundance and biomass.  However, these new approaches need verification for broad applicability.  Annual estimation of fish abundance has occurred in a suite of small, boreal lakes at the Experimental Lakes Area (ELA) for many years.  These well-defined fish populations present a unique opportunity to compare with concurrent acoustic assessments in a number of lakes.  We compared lake trout abundance and distribution data achieved through traditional annual mark-recapture methods (Jolly-Seber) and acoustic telemetry, respectively, to mobile fishery acoustic surveys.  Preliminary analyses show high correspondence between mark-recapture estimates of lake trout abundance and estimates derived from mobile surveys.  Further, the location of hydroacoustic fish detections during mobile surveys overlap well with core areas of habitat use by lake trout.  A second approach we have undertaken is the use of stationary hydroacoustic stations to assess foraging and activity patterns of top predatory species.  We first acquired estimates of lake trout activity determined through use of acoustic telemetry transmitters that are explicitly designed to record the relative frequency of sudden, high acceleration movement characteristic of predatory behaviour, as well as regular activity.  Lake trout movement rates were similar for free-swimming fish with acceleration transmitters compared to that estimated from stationary hydroacoustic approaches.  Initial findings of these two projects are promising and suggest that hydroacoustic methods can provide accurate estimates of abundance and activity rates of fish under natural conditions.