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Use of Gill Nets for Target Verification of a Hydroacoustic Fisheries Survey and Comparison with Kokanee Spawner Escapement Estimates from a Tributary Trap
Author(s) -
Baldwin Casey M.,
McLellan Jason G.
Publication year - 2008
Publication title -
north american journal of fisheries management
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.587
H-Index - 72
eISSN - 1548-8675
pISSN - 0275-5947
DOI - 10.1577/m07-182.1
Subject(s) - escapement , tributary , fishery , target strength , environmental science , abundance (ecology) , limnetic zone , oncorhynchus , fish <actinopterygii> , spawn (biology) , biology , ecology , geography , littoral zone , cartography
The focus of this study was to determine whether gill nets are a valid method for assessing species composition for a hydroacoustic survey and whether the hydroacoustic and gill‐net survey could be used to forecast the spawn escapement of kokanee Oncorhynchus nerka so as to allow fisheries managers to plan ahead for egg takes at Sullivan Lake, Washington. We conducted a mobile hydroacoustic survey of the limnetic zone of Sullivan Lake in September 2003. Species composition was estimated using floating, sinking, and suspended horizontal and vertical gill nets. Spawning escapement was estimated from a weir, trapping, and carcass recovery effort in Harvey Creek, the only spawning tributary of Sullivan Lake. Fish captured in gill nets ranged from 110 to 579 mm total length (TL), but 82% of the fish captured were between 150 and 290 mm TL. Kokanee were the dominant fish species captured in the limnetic gill nets, comprising 77% of the fish captured between 150 and 290 mm TL and 90% of the fish captured between 240 and 290 mm TL. We derived four alternative estimates of age‐3 kokanee abundance to account for the uncertainty in estimating the target strength of individual fish and the percentage of kokanee from the gill‐net catch. The acoustic and gill‐net abundance estimates that did not take into account the uncertainty in estimating kokanee length from target strength were relatively consistent (1–16%) with the Harvey Creek spawning escapement estimate (11,923). When abundance estimates were expanded by the average SE (25 mm) of individually tracked fish targets, the correspondence with the tributary spawn escapement was not as good (110–148%). This study showed that gill nets could be an effective means of verifying the acoustic targets of larger fish (>150 mm) and were adequate for forecasting spawn escapement for management purposes in our situation.