Assessment of the Performance of a Flat Panel Resistivity Fish Counter at Peterson Creek, 2007 and 2008

Alaska Department of Fish and Game, Fishery Data Series No. 12-78, Anchorage

To address the need for a reliable counting method to assess steelheadOncorhynchus mykiss abundance in remote index streams in Southeast Alaska, the Alaska Department of Fish and Game tested a Logie 2100C resistivity fish counter in Peterson Creek to count a small run of spring steelhead in 2007 and 2008. An above-water camera was used during daylight hours to record fish migrating over the white substrate panels to validate the resistivity counts. The video was also used to obtain fish lengths. The resistivity counter classifies signatures as either moving upstream, downstream, or as an event. Video validation revealed highly variable misclassification of fish movement in 2007. During 2007, upstream fish were correctly classified 45.9% of the time, and downstream fish were correctly classified 54.1% of the time. Further, the kelt emigration could not be accurately estimated because only 30% of the upstream fish were accounted for in the downstream count, despite a zero-count snorkel survey at the end of the run. The logarithm of fish length was not correlated with the peak signal size (PSS) of the counter (r² = 0.007), thus the size of steelhead outside of the video sample could not be estimated. The presumptive problem appeared to be a very low-stream conductivity ( = 13.9 µs/cm). A ratio estimator based on the 2007 video validation of number of fish passed to the number of fish detected (= 2.10) suggests that less than 50% of the fish passing the counter were detected. An abundance estimate was not generated for steelhead using this ratio because robust estimation of uncertainty was not possible. During the latter half of the 2007 and 2008 field seasons the electrode spacing was reduced in an attempt to amplify the counter signature and improve its function, but this change was not successful. The changes did not improve counter data misclassification so the 2008 data were not analyzed. We do not reccomend a resistivity fish for future use at this site.