Summary
The behaviour and survival of pike, Esox lucius L., released with a retained lure in the mouth was studied relative to control fish, which simulated line breakage prior to landing. Behaviour was monitored during the first hour post‐release with the aid of visual floats attached to the fish, and longer‐term for 3 weeks, by means of externally attached radio transmitters. Lure‐treated pike were less mobile during the first hour post‐release, but exhibited greater mobility and travelled further distances from the release area in the first 24 h after release than controls. From the second day after release, the behaviour of lure‐treated pike was similar to control fish. No mortality occurred in a 3‐week monitoring period. These results are indicative of only short‐term behavioural impairments resulting from a retained lure and rapid resubmission of normal behaviour after simulated break‐offs.
Methodology
The study was conducted in May 2006 (with angling between 3 and 19 May 2006) on Lake Opinicon, a large (787 ha), shallow (mean depth = 4.5 m), dimictic, mesotrophic, natural lake in eastern Ontario, Canada (44°33′56.0′ N, 76°19′23.6′ W). The gear and angling methods used to capture pike were intended to reflect common tactics used by anglers (e.g. barbed hooks, Arlinghaus, Klefoth, Kobler & Cooke 2008). Pike were captured from a boat by medium‐action rods and multifilament (16.3 kg) test line. Fishing was conducted by actively casting or trolling a variety of artificial lures (see Arlinghaus et al. 2008 for details).
After hooking, fish were played for a fixed time of 60 s and then landed with a rubber net. After netting, the fish was placed into a cooler, filled with fresh lake water to minimise air exposure while unhooking. If the fish was deeply hooked, the barbed hook shank was cut with a wire cutter to minimise unhooking‐related injuries (Arlinghaus et al. 2008) and all lures (and hooks) were removed after capture.
The study involved monitoring post‐release behaviour at a common release site. This was done to expose all pike to the same release environment and to avoid site‐specific post‐release behaviours that could be associated with site fidelity of individual pike at the capture site. Pike were angled from randomly selected sites along the shoreline and over submerged macrophyte beds at distances of at least 250 m from the observation area. Fish from all treatment groups were returned to the common release site (fixed time in the cooler before release 10 min) for post‐release behavioural monitoring. Experimentation was limited to pike that appeared healthy (i.e. absence of fungal infections) and where injury associated with the angling gear was minimal (i.e. little or no bleeding). Also, only females were used (determined according to Casselman 1974) to avoid sex‐specific variation in behaviour.
To determine the impact of leaving an artificial lure in the mouth on the subsequent behaviour, one lure treatment group (n = 12) and one lure control group (n = 10) was established to which individuals were randomly allocated. All fish were subjected to attachment of a float and an external radio transmitter to assess behaviour. To monitor behaviour at a fine scale within the first hour post‐release, fish were fitted with a small, coloured Styrofoam float attached via a size eight J‐type hook on a monofilament nylon line (2.5 m long, 1.7 kg test line) into the superficial tissue posterior to the origin of the dorsal fin (Cooke & Philipp 2004). Radio transmitters (Model PD‐2 transmitters, Holohil Systems Inc., Carp, ON, Canada; weight in air = 3.7 g, 25 × 13 × 6 mm, battery life 6 months, 120 mm antenna wire) were externally attached to the fish to monitor movement activity in the first 3 weeks post‐release (described in detail in Cooke 2003). The entire process of attaching floats and transmitters lasted <3 min.