Determining the Presence of Hooks Inside White Sturgeon Using Metal Detector and Portable X-Ray Technology

Abstract

We examined the feasibility of using handheld metal detectors and portable X-ray technology to assess the occurrence and type of hooks ingested by White Sturgeon Acipenser transmontanus in the Hell’s Canyon reach of the Snake River, Idaho. Three hundred and fifty-two White Sturgeon were collected in the Hell’s Canyon reach using angling and setline techniques from 2009 to 2011. Thirty-one percent scanned positive for the presence of hooks inside them. We found the handheld metal detector accurately determined hook presence in White Sturgeon 97% of the time when verified with X-ray. Larger size-classes of fish had a higher occurrence of hooks inside them (>50%) than did smaller size-classes. Occurrence of hooks within White Sturgeon across the entire study area was similar from year to year, ranging from 25% to 33%. We estimated that 64% of hooks observed with X-ray images were consistent with gear used for White Sturgeon angling and 36% were consistent with gear used for Smallmouth Bass Micropterus dolomieu and steelhead Oncorhynchus mykiss angling. Five White Sturgeon previously captured with hooks inside them did not scan positive for hooks upon recapture, indicating that they had passed hooks through the digestive tract or out the abdominal cavity. Hook ingestion is relatively common within this population; however, additional investigations on deep-hooking, hook processing, and potential effects on fish health need to be conducted before drawing conclusions about effects on the population.

Received August 24, 2015; accepted April 13, 2016

Acknowledgments

Most importantly, we remember Larry Barrett, an author on this paper, as the true Sturgeon General for his participation at the inception of this study and unending passion for White Sturgeon in Hell’s Canyon. Special thanks to the many volunteers and Idaho Department of Fish and Game staff who participated in data collection for this study. Finally, we thank Ed Schriever, Jim Fredericks, Kevin Meyer, Jeff Dillon, and three anonymous reviewers for their constructive comments and edits, which greatly improved the manuscript.