Summary
When break-offs occur during recreational angling, lures may be retained by the fish. To date, there have been few studies on the consequences of lure retention on sportfish. This study evaluated how the retention of three different types of lures (i.e., crankbait, jig and plastic worm—all with barbed hooks) influenced the behaviour, physiology and reproductive success of nesting, male smallmouth bass (Micropterus dolomieu) relative to controls released after lure removal. Bass were angled from their nests and subjected to a simulated lure retention scenario in which one of three lure types was placed in the upper middle jaw. Males were subsequently released and their behaviour (time to return to nest, parental care behaviour) was monitored. Immediately after release, fish with retained lures exhibited altered behaviour relative to control fish, attempting to expel the lure. However, these differences in behaviour were no longer apparent after 24 h even for those fish that retained the lures. Rates of nest abandonment did not differ between treatment and control fish in the short term. Fish were rarely able to liberate themselves from the retained lure in the several days post-treatment. Physiological sampling conducted on jig treatment fish and angled controls revealed elevated blood glucose concentrations in fish that had retained lures for 24 h, while lactate concentrations and hematocrit did not differ between treatment and control fish. These results demonstrate that lure retention in the short-term influences both the behaviour and physiology of smallmouth bass. Given that lures were generally retained throughout the study period, there may be merit in anglers using barbless hooks that may be more readily shed by fish that break the line, reducing the welfare impacts associated with lure break-offs on wild fish. Additional studies are needed to understand the longer term consequences of lure retention in free-swimming fish.
Methodology
This study was conducted in southeastern Ontario on Indian Lake (mean depth = 10 m, maximum depth = 26 m, 44°36′00″N, 76°20′00″W) from May 20 to 24, 2008. To assess the consequences of lure retention on parental care providing male smallmouth bass, nests with males present were located using snorkel surveys in the littoral zone surrounding four small islands. Only nests with males present, guarding broods, consisting of fresh eggs, with an egg score (categorical estimate of the number of eggs in a nest from 1 to 5, low = 1, high = 5) (Kubacki, 1992) from 3 to 4 were included in the study. All accepted nests were marked with individually numbered polyvinyl chloride tiles for easy identification (Kubacki, 1992). The 67 nests included in the study were randomly assigned to one of five experimental groups: (I) non-angled control (herein called “control”) fish which consisted of individuals that were observed but never angled from the nest (n = 11), (II) angled controls (herein called “sham”) that were angled from their nest but did not receive lure treatment (n = 15) and the remaining groups, (III) crankbait (n = 11; Fig. 1A), (IV) jig (n = 20; Fig. 1B) and (V) plastic worm (n = 10; Fig. 1C) represented simulated break-off conditions. Detailed descriptions and images of the lures can be found in Fig. 1.This study was conducted in southeastern Ontario on Indian Lake (mean depth = 10 m, maximum depth = 26 m, 44°36′00″N, 76°20′00″W) from May 20 to 24, 2008. To assess the consequences of lure retention on parental care providing male smallmouth bass, nests with males present were located using snorkel surveys in the littoral zone surrounding four small islands. Only nests with males present, guarding broods, consisting of fresh eggs, with an egg score (categorical estimate of the number of eggs in a nest from 1 to 5, low = 1, high = 5) (Kubacki, 1992) from 3 to 4 were included in the study. All accepted nests were marked with individually numbered polyvinyl chloride tiles for easy identification (Kubacki, 1992). The 67 nests included in the study were randomly assigned to one of five experimental groups: (I) non-angled control (herein called “control”) fish which consisted of individuals that were observed but never angled from the nest (n = 11), (II) angled controls (herein called “sham”) that were angled from their nest but did not receive lure treatment (n = 15) and the remaining groups, (III) crankbait (n = 11; Fig. 1A), (IV) jig (n = 20; Fig. 1B) and (V) plastic worm (n = 10; Fig. 1C) represented simulated break-off conditions. Detailed descriptions and images of the lures can be found in Fig. 1.
Sham controls and lure treated groups were angled from within 5 m of their nests in <20 s using heavy-action recreational fishing gear. All fish were initially captured using barbless jigs and we restricted our efforts to fish that were shallowly hooked (i.e., jaw) and exhibited no bleeding and minimal tissue damage (just the hook penetration site). Fish were then placed in a padded v-shaped trough filled with fresh lake water where the lure was removed and total length of fish recorded (to the nearest cm). Crankbait treated fish were released with a positively buoyant, double number four sized treble hook crankbait with a single posterior hook placed in the jaw of the fish using pliers. Fish in the jig treatment were released with a lead dart style jig with a 1/0 barbed hook with a soft plastic twister tail. Worm treatments consisted of a 1/0 worm hook with a soft plastic worm. Pliers were used to place the lures in the upper jaw. Processing time from landing to release of fish was completed within 2 min in all cases, while a diver remained near the nest preventing brood loss through predation. Air exposure was limited because all sampling and handling occurred in water thus emulating the lack of air exposure that would occur in a break-off scenario.