Incidence, Types, and Shedding and Ingestion Times of Metallic Fishing Tackle in the Digestive Systems of White Sturgeon

Abstract

Over the last decade, fishing tackle has been documented in the digestive tracts of White Sturgeon Acipenser transmontanus in several fisheries in the Columbia River basin, raising concerns about the prevalence and types of tackle being consumed and the ability of these long‐lived fish to shed such metal in a timely manner. We scanned 2,077 White Sturgeon with a metal detector and X‐rayed (with a portable X‐ray system) 443 fish in the Hells Canyon reach of the Snake River to characterize the incidence, quantity, and type of hooks and other metal fishing tackle that had been ingested. We also estimated the amount of time for fish to eliminate ingested metal and to ingest new metal. For the fish we captured, which averaged 118 cm and ranged from 47 to 287 cm (fork length), 21% contained metal in their digestive tract, with smaller fish (<100 cm) less likely to contain metal (10%) than larger fish (>100 cm; 36%). Much of the metal in the digestive systems of White Sturgeon was fishing tackle that was not gear targeting White Sturgeon and included large and small hooks, jigs, swivels, and pieces of broken metal. White Sturgeon with metal in their digestive systems, on average, weighed slightly less than fish without metal, suggesting that metal may slightly hinder food consumption or assimilation, though this affect was apparently short lived. White Sturgeon X‐rayed at least twice over the course of the study were able to pass ingested metal on average in 492 d, but one piece of metal was retained for at least 1,266 d. White Sturgeon ingested new metal on average every 575 d. In summary, our results suggest that White Sturgeon effectively process the metal they ingest, and that most if not all their metal passage is by oxidation through the digestive system.

Using a handheld metal detector to detect ingested hooks and other metallic objects in freshwater turtles

“…However, hooks imbedded in visceral tissue in fish are less likely to decay than hooks exposed to seawater (Aalbers et al 2004). Certain fish can shed hooks primarily through internal oxidation, although this process can take around 16 months in white sturgeon (Lamansky et al 2018).…”

“…However, hooks imbedded in visceral tissue in fish are less likely to decay than hooks exposed to seawater (Aalbers et al 2004). Certain fish can shed hooks primarily through internal oxidation, although this process can take around 16 months in white sturgeon (Lamansky et al 2018). Transit times for ingested hooks were much faster in Kemp's ridley sea turtles ( Lepidochelys kempii ), with average transit times of 4–13 days depending upon hook location within the gastrointestinal tract (Heaton et al 2016).…”

“…Additionally, we only studied the efficacy of the handheld metal detector on small turtles; efficacy may decline on larger animals (e.g., sea turtles). While handheld metal detectors have successfully detected hooks in large fish (e.g., white sturgeon, Lamansky et al 2018), signal strength may decline as a function of turtle shell depth and bone density and requires additional study.…”

“…Handheld metal detectors have been successfully used to detect hooks inside white sturgeon (Acipenser transmontanus) in the field confirmed via follow-up radiographs (97% accurate; Bowersox et al 2016). In a similar study, Lamansky et al (2018) scanned 2,077 white sturgeon and achieved 90% accuracy in detecting hooks.…”