Estimating freshwater turtle mortality rates and population declines following hook ingestion

Abstract

Freshwater turtle populations are susceptible to declines following small increases in the mortality of adults, making it essential to identify and understand potential threats. Freshwater turtles ingest fish hooks associated with recreational angling, and this is likely a problem because hook ingestion is a source of additive mortality for sea turtles. We used a Bayesian-modeling framework, observed rates of hook ingestion by freshwater turtles, and mortality of sea turtles from hook ingestion to examine the probability that a freshwater turtle in a given population ingests a hook and subsequently dies from it. We used the results of these analyses and previously published life-history data to simulate the effects of hook ingestion on population growth for 3 species of freshwater turtle. In our simulation, the probability that an individual turtle ingests a hook and dies as a result was 1.2-11%. Our simulation results suggest that this rate of mortality from hook ingestion is sufficient to cause population declines. We believe we have identified fish-hook ingestion as a serious yet generally overlooked threat to the viability of freshwater turtle populations.

Conservation implications of turtle declines in Australia’s Murray River system

“…Adult turtles are overharvested for both human consumption and the pet industry 11,12 , can experience high road mortality 13,14 , and are killed by human-introduced predators when they nest or disperse 10,15 . Turtles are struck by boats 16 , drowned in fishing nets and other human structures 17,18 , and wounded or killed by anglers 19,20 . Mortality of eggs and young has also increased, primarily because of poaching and predation by introduced predators 9,21,22 .…”

Using Local Ecological Knowledge in Louisiana to Infer Distribution and Abundance of the Alligator Snapping Turtle

“…Therefore, it seems possible that incidental drowning on trot lines, limb lines, and submerged hoop nets (or even ingestion of fish hooks after being cut off a fishing line) could be a major source of contemporary mortality in southwestern Louisiana. Ultimately, this could threaten the long‐term population viability of alligator snapping turtles as a result of lowered annual adult survival rates (Folt et al , Steen and Robinson ).…”

“…For the latter, Huntzinger et al () reported a dead alligator snapping turtle on a limb line, while several of our questionnaire responses also mentioned finding alligator snapping turtles dead on trot lines or in nets. Enge et al () found 12–36% of alligator snapping turtles radiographed in Florida, USA, contained ingested fish hooks, while Steen and Robinson () estimated that the mortality rates of alligator snapping turtles could be as high as 6% after ingesting fish hooks, leading to a 64% increase in the probability that a population will decline. Therefore, it seems possible that incidental drowning on trot lines, limb lines, and submerged hoop nets (or even ingestion of fish hooks after being cut off a fishing line) could be a major source of contemporary mortality in southwestern Louisiana.…”

Freshwater turtle by-catch from angling in New Brunswick, Canada

“…The extirpation of Eastern Musk Turtle (Sterno therus odoratus) around the city of Hamilton, Ontario, is believed to have been the result of angling combined with habitat modification (Lamond 1994cited in COSEWIC 2012. Steen and Robinson (2017) dem onstrate that in settings where recreational fishing pressure is intense, hooking by anglers could have a great enough impact to affect populations. Steen et al (2014) x-rayed over 600 turtles from five rivers in the southeastern United States and found that the prevalence of ingested fish hooks ranged from 0% to 33% depending on species, sex, age class, and site; the highest rate, 33%, was for adult female Snapping…”