Physiological disturbances and behavioural impairment associated with the incidental capture of freshwater turtles in a commercial fyke-net fishery

Abstract

Turtles are caught as bycatch in commercial fisheries in both inland and marine waters. Turtle mortality associated with bycatch is concerning, as life-history characteristics of turtles, including high juvenile mortality and delayed sexual maturity, make them particularly susceptible to population declines following small increases in adult mortality. In eastern Ontario, Canada, freshwater turtles are encountered as bycatch in an inland commercial fyke-net fishery. Although some temperate turtle species can tolerate prolonged submergence, their ability to withstand submergence decreases as water temperatures increase such that turtles may experience severe physiological disturbances and mortality following prolonged forced submergence. The purpose of our study was to evaluate the sublethal physiological consequences and related behavioural impairments associated with fyke-net capture for 3 species of freshwater turtles (eastern musk turtle Sternotherus odoratus, northern map turtle Graptemys geographica and painted turtle Chrysemys picta). Individuals that were entrapped for 3 h at elevated water temperatures (23 to 29°C) displayed considerably higher blood lactate and lower blood pH compared to freeliving individuals. This trend was consistent across species and sexes. Despite having the largest increase in blood lactate, musk turtles did not exhibit behavioural impairment from entrapment, whereas both map and painted turtles displayed low responsiveness to behavioural assessments following entrapment. Our results suggest that sub-lethal responses can be used to identify potential harm or fitness impacts even in the absence of immediate mortality. Assessment of behavioural impairments, which could compromise activity and potentially result in post-release mortality, is important for protected and at-risk species that exhibit high juvenile mortality and delayed sexual maturity.

The social, economic, and environmental importance of inland fish and fisheries

“…There are numerous examples of overfishing of inland fish populations (Allan et al 2005) and instances of unwanted bycatch (e.g., MacMillan and Roth 2012; Stoot et al 2013). Likewise, some negligent inland aquaculture practices can have significant impacts on the environment, such as nutrient loading, release of cultured species, and propagation of disease (Kapuscinski and Brister 2000).…”

Refinement of bycatch reduction devices to exclude freshwater turtles from commercial fishing nets

“…The device did not appear to have a significant effect on the CPUE for musk turtles even though a 38.3% reduction was observed and the turtles collected were significantly smaller (Table 1). This high capture rate for musk turtles is unexpected based on the success Larocque et al (2012b) had with 8 cm devices, and is concerning despite the better tolerance of submergence by this species (Stoot et al 2013). Only 2 snapping turtles were collected, both in unmodified nets.…”

“…Bycatch is the inadvertent capture of non-target species and is a major issue in commercial fisheries in marine and freshwater environments around the globe (Saila 1983, Alverson et al 1994, Raby et al 2011. Bycatch occurs as a result of overlap in spatial distribution between target and non-target species, and the use of gear lacking the selectivity to differentiate between them.…”

Biologgers reveal post‐release behavioural impairments of freshwater turtles following interactions with fishing nets

“…We used six behavioural tests (Table 2 in Stoot et al ., ) which assessed escape ability, righting ability (on both land and water), response to startles (audible/pressure and visual) and tactile stimuli to the head, limbs, and tail. The response was scored as present if the individual responded to the stimulus (1) or otherwise absent (0).…”

“…Despite the ability of freshwater turtles to withstand extended periods of submergence, prolonged entrapment in fishing nets can result in drowning (Larocque et al ., ). In addition, acute physiological and behavioural impairments can occur as a result of entrapment in fyke‐nets (LeDain et al ., ; Stoot et al ., ), although this has not been assessed in free‐ranging animals. Turtles are particularly susceptible to population declines following slight increases in adult mortality, such as bycatch mortality, because of their naturally high juvenile mortality and delayed sexual maturity (Congdon, Dunham & Van Loben Sels, , ; Gibbons et al ., ).…”