Abstract
Representative indices of population abundance for at-risk species are necessary to inform conservation decision-making. Many madtoms (Noturusspp.) are considered imperiled; however, the efficacy of frequent monitoring efforts has been questioned due to their cryptic and nocturnal behaviors. We systematically evaluated a madtom monitoring tool by (1) evaluating the use of small (8 × 2 mm), surgically implanted 125 kHz passive integrated transponder (PIT) tags for frecklebelly madtomN. munitusand (2) assessing the effectiveness of a radio-frequency identification (RFID)-enhanced artificial cover unit to index madtom abundance. Surgically implanted PIT tags had no apparent influence on madtom survival between 45 and 110 mm total length, and all tags were retained throughout a 21 d laboratory study. In experimental mesocosms, the enhanced cover units confirmed occupancy during nearly all replicates (77.6%), even at extremely low densities (n = 2 madtoms). The enhanced cover units provided representative estimates of madtom relative abundance (p < 0.01), whereas catch per unit effort was not significantly associated with previously validated visual observations (p = 0.12). Although madtom density and the number detected using the enhanced cover units were correlated, the gear was potentially saturated at relatively high densities (~20 fish per mesocosm) when deploying a single unit. In most cases, occupancy was confirmed within 12 h, and nearly half of the individuals were detected within ~72 h. Small PIT tags and RFID-enhanced artificial cover units offer novel opportunities to efficiently describe the ecology and population dynamics of madtoms.
Highlights
Little ecological knowledge exists for many smallbodied, non-game fish despite these being disproportionately represented by species at risk of extinction (Burkhead 2012, Cooke et al 2012)
The availability of smaller passive integrated transponder (PIT) tags may improve our understanding of small-bodied fish ecology, but their suitability has yet to be extensively tested for many taxonomic groups
Small PIT tags paired with artificial cover units may offer opportunities to improve our understanding of madtom ecology and evaluate the effectiveness of management actions, but the suitability of such tags has not been tested
Summary
Little ecological knowledge exists for many smallbodied, non-game fish despite these being disproportionately represented by species at risk of extinction (Burkhead 2012, Cooke et al 2012). Artificial cover units attract individuals which can be visually inspected to inform occupancy analyses and to estimate relative abundance (Midway et al 2010a, Cope et al 2019) It is uncertain if the number of madtoms encountered at one time in a cover unit is related to local abundance. The availability of smaller PIT tags may improve our understanding of small-bodied fish ecology, but their suitability has yet to be extensively tested for many taxonomic groups These tags offer little advantage for species that are difficult to detect or recapture following implantation. Small PIT tags paired with artificial cover units may offer opportunities to improve our understanding of madtom ecology and evaluate the effectiveness of management actions, but the suitability of such tags has not been tested. Conclusions generated from this research support an innovative method to inform future reintroduction and monitoring efforts for this and related madtom species
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