Comparing The Effectiveness Of Diurnal Rock-Lifting And Nocturnal Dive-Lighting Surveys For Eastern Hellbenders

ASU Author/Contributor (non-ASU co-authors, if there are any, appear on document)
Freddy Junior Ortega (Creator)
Appalachian State University (ASU )
Web Site:
Michael Gangloff

Abstract: Studies designed to better understand perceived hellbender population declines typically use diurnal rock-lifting surveys to detect individuals. However, these methods are invasive as they may alter sheltering or breeding habitat or result in injuries to hellbenders and surveyors. Further, diurnal surveys omit bedrock and large boulders that cannot be lifted. Between the months of June and August, 2019, I compared the number of detections and catch per unit effort (CPUE) of nocturnal snorkel surveys, followed by traditional diurnal rock-lifting surveys across 11 sites within the New, Watauga and Nolichucky river drainages in Western North Carolina. An additional late August - late September pass was conducted to reveal any breeding period effect on nocturnal detection rates. Wilcoxon signed-rank revealed that number of animals detected did not vary with method (diurnal to nocturnal summer: (Z = 37, df = 10, P = 0.08); nocturnal summer to nocturnal breeding: (Z = 9, df = 7, P = 0.68). Detections increased in 63% of sites during nocturnal surveys in both summer and breeding nocturnal surveys when compared to diurnal rock-lifting surveys. Paired t-tests comparison of hellbender catches across three survey treatments revealed that CPUE was statistically higher in the nocturnal summer treatment (t = 2.69, df = 9, P = 0.025); this difference was not observed between nocturnal-summer and nocturnal-breeding surveys (t = - 0.95, df = 7, P = 0.37). During nocturnal snorkel surveys, CPUE increased in 82% and 88% of sites for early summer and late summer treatments with 26% and 13% of detections being individuals sheltering in bedrock crevices during early summer and late summer nocturnal surveys respectively. Contrastingly, during early summer diurnal surveys, all detections were from beneath boulder substrate. By targeting the period of highest presumed activity in these cryptic salamanders, I was able to obtain more representative enumeration estimates of populations size likely because detection probabilities were equal or higher at most sites. These results suggest that both methods are similarly effective at detecting hellbenders. However, nocturnal surveys have the advantage of minimizing microhabitat impacts and are more efficient in terms of search effort. Additionally, non-invasive sampling can also be used to conduct surveys during the breeding season when nesting animals would presumably be more sensitive to disturbance associated with rock-lifting.

Additional Information

Ortefa, F. (2020). Comparing The Effectiveness Of Diurnal Rock-Lifting And Nocturnal Dive-Lighting Surveys For Eastern Hellbenders. Unpublished Master’s Thesis. Appalachian State University, Boone, NC.
Language: English
Date: 2020
amphibians, hellbender, nocturnal, survey methods, rock-lifting, monitoring

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