We examined the physiological and behavioural consequences of, and recovery from, catch-and-release related stressors using a combined laboratory and field study in northern pike (Esox lucius L.). A laboratory experiment was conducted to investigate the recovery dynamics of physiological indicators of stress resulting from a simulated angling event resulting in exhaustion, with and without additional air exposure of 300 s. In addition, a field study using a combination of physiological and behavioural assessment was conducted to assess the long-term consequences of exhaustive exercise and various air exposure durations. Exhaustive exercise for 60 s led to increased muscle lactate, decreased tissue energy stores, and alterations in plasma ionic status. Recovery from physiological disturbance was rapid with all physiological variables except plasma glucose returning to baseline levels after 6 h. The recovery profile was largely unaffected by air exposure of 300 s that simulated extended de-hooking time. The field component of our study verified the impact of exhaustive exercise on blood lactate values, but did not detect any impact of air exposure varying between 0 s and 300 s on physiological stress indicators. However, pike exposed to air for 300 s were behaviourally impaired in the first hour post-release indicating that despite limited effects on physiological status air exposure resulted in significant impairment of organismal performance. Behavioural patterns returned to normal within several hours. In a three-week post-release monitoring period no mortality occurred. Our results emphasize that angling-induced stressors result in physiological and behavioural disturbances, but that recovery is quick. This suggests that pike are relatively resilient to catch-and-release related stressors but air exposure durations should be kept <300 s to minimize behavioural impairment.
Study area and pike angling
The study was carried out between May 3 and June 1, 2006 at Lake Opinicon, a shallow (mean depth = 4.5 m, size 787 ha), dimictic, mesotrophic natural lake in eastern Ontario, Canada (N 44°33′56.0″ W 76°19′23.6″). The laboratory component of this study used facilities at the Queen's Biology Station at Lake Opinicon using fresh lake water. Pike used in the study were captured by angling from a boat in Lake Opinicon using medium-action spinning rods and multifilament line (16.3 kg test). Angling was conducted by actively casting or trolling a variety of artificial lures, and all lures were fished with at least one treble hook (see Arlinghaus et al., 2008a for details). Upon hooking, captured pike were landed in a rubber net to minimize handling related injuries (Barthel et al., 2003). Playing time was standardized to 60 s, which constitutes an average playing time for smaller-sized pike allowing safe landing and handling (Schwalme and Mackay, 1985a, DuBois et al., 1994).
A laboratory experiment was conducted to assess the recovery dynamics of physiological variables in pike following exercise, and to assess if this recovery profile was significantly altered by a 300 s period of air exposure. This air exposure duration was chosen as it represents the worst-case scenario of air exposure that could be experienced by pike during an angling event (DuBois et al., 1994). Pike used for the laboratory experiment were captured in Lake Opinicon as explained above. Unhooking was done under water within a cooler filled with fresh lake water to avoid air exposure, and fish were transported alive into the laboratory. In the laboratory, pike were stocked into darkened fibreglass holding aquaria (153 cm × 62 cm × 57 cm; water exchanged twice per hour) supplied with fresh, fully oxygenated Lake Opinicon water for 48 h prior to experimentation. During the experiments, water quality was measured daily every three hours and was as follows: mean oxygen concentration ±SD: 8.5 ± 0.5 mg l−1 (range 7.5–9.5 mg l−1); mean water temperature ±SD: 18.6 ± 2.7 °C (range 15.1–22.9 °C).
To generate control (resting) physiological values, individual pike were netted from the holding tank and transferred for 48 h to darkened, individual Perspex holding chambers (volume of approximately 12 l) continuously supplied with fresh lake water. After 48 h, the water supply to the chambers was terminated. To euthanize the individual pike, clove oil (250 ppm) was added to the chambers. Following cessation of ventilation, a blood sample and a white muscle sample was taken. Blood samples were collected using the caudal venipuncture technique (Houston, 1990). For this, a vacutainer syringe (38 mm, 21.5 gauge, lithium heparin) was used to draw 3 ml of blood from the caudal vessels (Cooke et al., 2005). Blood samples were briefly held in an ice–water slurry until they were centrifuged to obtain plasma within 10 min. Afterwards, they were placed in liquid nitrogen for later analysis (see below). Further, a white muscle sample (approximately 10 g of tissue from an elongate piece that ran laterally along the body of the fish) was taken from the epaxial musculature below the dorsal fin and above the lateral line using a scalpel immediately after the blood sample was obtained. This sample was transferred into vials and immediately placed in liquid nitrogen.