Summary
After a fish snaps an angler’s line, the hook(s) still embedded in its mouth, the question arises: what will the encounter cost the fish? The consequences of retained gear on the physiology and behaviour of fish is not well understood. This study aimed to quantify the impact of prolonged exposure to a retained lure (simulated break off in recreational angling) to the physiology and behaviour of northern pike (Esox lucius) was studied in a laboratory setting. A combination of blood-based physiological metrics and metabolic rate measurements were used to provide a comprehensive overview of the physiological consequences of lure retention in this species using two different treble hook sizes on metal casting spoons in three different hooking locations. Fine-scale video observations of pike following simulated break off were collected to assess pike interaction with a retained lure and to quantify activity patterns. We found that the retention of a lure did not significantly affect metabolic rate, blood physiology or locomotor activity of pike. However, gill ventilation rate was found to be elevated in pike hooked deeply in the throat suggesting that lures in obstructive locations may somewhat challenge recovery from exercise. Elevated cortisol levels in these fish compared to wild controls suggests that confinement produced prolonged stress in all treatments that may have affected the physiological and behaviour responses that we observed. Our findings provide important observations about the interpretation of stress-oriented laboratory studies using northern pike and the extrapolation of these results to the wild. Despite our negative findings in relation to lure impacts on pike physiology and behaviour, avoiding break offs would still be advisable for fish welfare reasons
Methodology
Study site and study animals
This study was conducted at the Queens University Biological Station (QUBS) in eastern Ontario, Canada, (44°31′N, 76°22′ W) in May and June 2008. Northern pike were collected from Lake Opinicon, which has an abundant natural pike population, by conventional hook-and-line angling from a variety of locations throughout the lake. Angling gear consisted of medium action spinning rods and reels spooled with 15–20 pound test line. Lures, consisting of spoons and artificial fish imitations (crank baits), were attached to the line with wire leaders and swivels. Angling involved casting and trolling with a target of collecting eight fish per day. On a given day, a number of locations were sampled to ensure that fish were not collected from the same area. Barbless hooks were used to minimize injury and to increase ease of hook removal (Alós et al., 2008). Upon capture, fish were immediately brought to the boat and netted keeping angling time shorter than 60 s. Fish that were angled for longer periods of time or to exhaustion were not included in the study. Following collection and hook removal, fish were visually assessed. Fish in good condition (i.e. no visible signs of excessive injury or bleeding) were retained and transported to the QUBS wet lab facility in an onboard live-well that was regularly refreshed with lake water.
At the QUBS wet lab, pike were held in three 1200 L (152 cm diameter) shaded flow-through holding tanks for 24 h to allow the fish to return to a baseline resting state, following methods similar to Suski et al. (2007). Fish were distributed among the three tanks to minimize density effects (no more than 5 fish per tank at any time). After a 24 h holding period, the fish were carefully netted from their tank and randomly allocated to control or treatment groups. The one variation on this approach was the lake controls which were captured and sampled for blood immediately upon netting into the boat. An individual fish was only used once.
Experiment 1: effect of lure retention on recovery after exercise
To quantify the effects of lure retention on recovery after exhaustive exercise, we used a conventional chasing protocol to induce physiological disturbances and thereby simulate a C&R event. Pike were removed from the 24 h holding tanks and then exercised for 60 s using tail pinches (Suski et al., 2007, Arlinghaus et al., 2009) in a circular (92 cm diameter) tank half-full of lake water. Following exhaustive exercise, pike in all treatment groups were netted, transferred to a foam-padded v-shaped trough filled with fresh lake water and a lure treatment was applied. Six groups of treatment fish were differentiated: (1) a small spoon (5 cm blade length [bl], #6 Mustad barbed treble hook) hooked in the lower jaw; (2) a small spoon hooked into the throat (tissue at the base of the tongue); (3) a small spoon hooked in both the upper and lower jaw; (4) a large spoon (12 cm bl, #3/0 Mustad barbed treble hook) hooked in the lower jaw; (5) a large spoon hooked into the throat; and (6) a large spoon hooked in both the upper and lower jaw (Fig. 1). Hooks were placed into position using pliers and pushed through the tissues with a direct unidirectional application of force to simulate hooking that would occur during an angling event.
Experiment 2: effect of lure retention on metabolic rate
To quantify the effect of hooking treatment on metabolic rate, a 12 h static respirometry assessment was completed using pike assigned to a set of treatment and control conditions similar to those used in Experiment 1. For this portion of the study, pike were subjected to one of the following three treatments: (1) a small spoon hooked in the lower jaw (n = 5; mean fork length 467 ± 24 mm); (2) a small spoon hooked in both the upper and lower jaw (n = 7; mean fork length 502 ± 49 mm); (3) a large spoon hooked in both the upper and lower jaw (n = 4; mean fork length 517 ± 38 mm); and a control, where the fish received no lure (n = 13; mean fork length 483 ± 48 mm).