Assisted recovery following prolonged submergence in fishing nets can be beneficial to turtles: An assessment with blood physiology and reflex impairment

Animals

Using fyke nets, we captured 34 male painted turtles (Chrysemys picta; mean mass ± SE: 335 ± 5 g, range: 276–394 g; mean carapace length ± SE: 142 ± 1 mm, range: 121–151 mm) in Lake Opinicon, Ontario, Canada (44°34′N, 76°19′W) from 6 to 21 June 2011. Fyke nets were set for 24 hrs in water approximately 1 m deep and were fished such that the lead line and wings acted as guides into the nets (see Larocque et al. 2012a for net dimensions and set details). Floats in the nets were used to create air spaces for turtles and other organisms (Larocque et al. 2012b).After capture, turtles were held outdoors at the Queen's University Biological Station in flow-through tanks (1-m³ circular holding tanks containing ∼700 l of lake water) between 24 and 72 hrs prior to being used in the experiment. All tanks contained floating wood platforms onto which turtles could climb to bask. Turtles were not fed while in captivity, nor disturbed.

Experimental Procedure

We used 4 treatment groups to elucidate whether turtles, after being completely submerged for a long duration, differed in recovery in or out of water: 1) unsubmerged controls (baseline response), 2) immediately after submergence, 3) recovery in water, and 4) recovery out of water. Turtles did not vary in mass or size between treatments (mass, F_3,26  =  0.82, R²  =  0.09, p  =  0.50; carapace length, F_3,26  =  1.55, R²  =  0.15, P  =  0.15). For each treatment, turtles were sampled for blood lactate and pH (indicators of anoxia) as well as reflex responses. Ten control turtles were sampled after the holding period in the flow-through tanks to obtain baseline values. Otherwise, the rest of the turtles were individually submerged within indoor tanks (155 by 55 by 60 cm) containing lake water for 12 hrs. Turtles were submerged within the tank by enclosing them in a cage (75 by 40 by 30 cm) made of 5.1-cm² plastic mesh. Water temperatures were maintained between 24°C and 26°C, and dissolved oxygen was at ambient levels (typically 6–8 mg l⁻¹). A 12-hr submergence period at these temperatures is near the critical limit that painted turtles can withstand anoxic submergence (Musacchia 1959; Herbert and Jackson 1985). It is worth noting that, in Ontario, fishers have to check nets at most every 48 hrs, so much longer submergence is possible in the commercial fishery. Nevertheless, we had to balance realism with animal care and conservation concerns. Four turtles were not capable of withstanding 12 hrs of submergence (see “Results”) based on a sublethal endpoint (i.e., lack of movement). Ability to withstand the submergence period was periodically assessed visually and with gentle prodding (if necessary to determine movement) to try to ensure the turtle's survival (if a turtle appeared in distress, it was checked at least every half hour). After the 12-hr submergence period, we released turtles from the submerged cage. Six turtles were immediately sampled after the submergence period. The remaining turtles were placed in a tank (1 m³) of water and allowed 1 hr to recover prior to sampling. During the recovery period, seven turtles recovered out of water while placed on a 25 by 20-cm floating Styrofoam platform, while 7 turtles recovered in the water with no floating platform provided. A 1-hr recovery period was chosen for 2 reasons: a recovery period longer than 1 hr is not likely to be practical for fishers and blood pH is typically restored to normal values by this time period at the water temperatures used (Herbert and Jackson 1985).