Summary
Recently, there has been growing recognition that fish harvesting practices can have important impacts on the phenotypic distributions and diversity of natural populations through a phenomenon known as fisheries-induced evolution. Here we experimentally show that two common recreational angling techniques (active crank baits versus passive soft plastics) differentially target wild largemouth bass (Micropterus salmoides) and rock bass (Ambloplites rupestris) based on variation in their behavioural tendencies. Fish were first angled in the wild using both techniques and then brought back to the laboratory and tested for individual-level differences in common estimates of personality (refuge emergence, flight-initiation-distance, latency-to-recapture and with a net, and general activity) in an in-lake experimental arena. We found that different angling techniques appear to selectively target these species based on their boldness (as characterized by refuge emergence, a standard measure of boldness in fishes) but not other assays of personality. We also observed that body size was independently a significant predictor of personality in both species, though this varied between traits and species. Our results suggest a context-dependency for vulnerability to capture relative to behaviour in these fish species. Ascertaining the selective pressures angling practices exert on natural populations is an important area of fisheries research with significant implications for ecology, evolution, and resource management.
Methodology
Two different angling methods were used to collect 100 rock bass (total length, 180–275 mm [mean = 205 mm]; mass, 50–345 g [mean = 168 g]) and 100 largemouth bass (total length, 166–470 mm [mean = 301 mm]; mass, 68–1470 g [mean = 454 g]) from numerous locations comprising similar habitats (i.e. shallow bays with open water with weed cover below) in Lake Opinicon, Ontario, Canada (44°33′56.0” N, 76°19′23.6” W) between 3 July and 14 August 2014. Lake Opinicon was chosen as Centrarchids are subject to extensive recreational angling pressure year round and is therefore ideal for the purposes of our study. In-lake capture locations were separated by hundreds of meters to kilometres and were such that the breadth of this large lake was sampled, ensuring an accurate representation of the lake populations. Water temperatures were high yet stable during this summer study period (range: 24–26°C). Equal numbers of each species were caught using each of the two angling techniques (n = 50/technique/species), brought back to the laboratory and tested for individual level differences in standard metrics of personality [11, 14]; namely refuge emergence time [32, 33], flight-initiation-distance (FID) [34], general activity [35] and latency-to-recapture with a net [36] in the test arena. For both methods, angling was conducted using 2-m-long, medium-strength fishing rods and reels equipped with 4.5 kg break-strength, braided fishing line, which is typical gear for anglers targeting these species. For method one, terminal tackle included several different manufacturers’ brightly coloured diving or lipless 5–7 cm crank baits equipped with two size 4 treble hooks that were fished actively (Fig 1). These crank baits exhibited variable motion paths in the water and/or contained ‘rattles’ and were also capable of alternately floating and diving rapidly or ‘wiggling’ near the surface when retrieved. For method two, terminal tackle included a 1/0 circle hook, baited with a naturally coloured (e.g. leech [brown-green], pumpkin [brown], watermelon seed [dark green], wasp [dark red] or June bug [purple- black]) 12.7 cm ‘wacky-rigged’ plastic worm that was fished passively (Fig 1). Plastic baits were ‘wacky-rigged’ with a simple hook and O-ring, and in contrast to cranks baits, were silent (no rattles and sunk gradually when not being retrieved) and fished more passively (slow retrieval).
When a fish strike was detected (using either method)by the angler, the hook was set into the fish’s mouth as per typical angling events and the fish was landed as quickly as possible either by hand or using a rubberized fishing net. Our protocol was such that we aimed to have fish de-hooked and recovering in large coolers (containing fresh lake water, 45–90 litre) within ~45 s of initial strike to minimize fish stress from angling or air exposure. When possible, hooks were removed underwater and air exposure did not exceed 20 seconds, a duration which is deemed to be minimally stressful for these species [37, 38]. Fish that were deeply hooked or bleeding were not used in the study and immediately released. All fishing for both species occurred simultaneously, in the same areas and habitat types (though some unobservable variation in micro-habitats might exist between species/ sampling sites) and using the same lures to avoid a sampling bias associated with location of capture, habitat characteristics (submergent cover, rocks, emergent vegetation etc.) or lure type outside of our initial predictions. Fish that were caught using either of the two angling methods were held in separately marked coolers that had regular water exchanges prior to being brought back to the laboratory, where they were held in similarly marked holding tanks (see below). All fish were individually marked each day by clipping a small amount (<5mm) of one of the first 4 dorsal spines on the dorsal fin. Sampling (fishing) occurred everyday during the experimental period between the hours of 8am and 8pm. Once the daily maximum of 8 test fish was caught (of either species), sampling for that given day ceased. In general, largemouth bass were 2-3x more likely to be caught using either angling method than rock bass, which likely has to do with species abundance in the given sampling areas.