Summary
Selectively removing fish based on particular traits, such as body size, may shift trait abundance in the remaining population, resulting in a phenomenon called fisheries-induced evolution. Recently, there is growing interest in evaluating the effects of fisheries-induced evolution on fish behaviour. Aquatic protected areas (APAs) have been designated in some habitats in efforts to prohibit harvesting and maintain natural ranges of phenotypic variation for impacted species. Here, we attempted to test whether APAs that prohibit all forms of fishing have an evolutionary influence on adult largemouth bass (Micropterus salmoides) behaviour by investigating the relationship between capture method and behavioural type. Fish, caught via active (angling) and passive (hoop net) capture techniques in both protected (70+ year old APAs in eastern Ontario) and adjacent nonprotected areas, were subjected to standard tests of boldness (refuge emergence, general activity, and flight-initiation-distance). A behavioural syndrome characterized by consistent within-individual variation and correlation of boldness behaviours (activity and refuge emergence) was present. Our results provide evidence that APAs may promote behavioural diversification and protect traits selectively targeted by recreational angling.
Methodology
Between 18 May and 12 June 2015, we captured 105 adult largemouth bass using two different capture methods in Lake Opinicon, Ontario, Canada (44°33'32''N, 76°19'42''W) from several shallow bays inside and outside two APAs. This is an ideal study system, as largemouth bass are under intense seasonal recreational angling pressure. Lake Opinicon has two long-established (>70 years) year-round APAs located in isolated, well-marked bays at either end of the lake that prohibit all forms of fishing including catch-and-release angling. Lake Opinicon has a total area of 890 ha and its two sanctuaries, Murphy Bay and Darlings Bay, are 14.2 and 83 ha, respectively (Keast 1978). Lake Opinicon also reflects ideal largemouth bass habitat, as it is shallow and contains significant numbers of submerged tree trunks and stumps as a result of construction of the Rideau Canal and a corresponding rise in overall water levels (Karst and Smol 2000). There is also a commercial fishery that uses hoop nets outside the sanctuaries, and although largemouth bass cannot be harvested, bycatch mortality does occur (Colotelo et al. 2013). For this study, the first capture method involved actively angling 52 fish (total length 280–474 mm (mean = 361 mm)) using a “wacky-rigged” plastic worm setup. Another 53 individuals were caught passively using unbaited hoop nets (total length 280–451 mm (mean = 361 mm)). Hoop nets were used as our passive capture technique, as the gear does not move throughout the capture process (Hubert et al. 2012). Fish were caught using both capture methods inside (N = 52, total length 280–474 mm (mean = 365 mm)) and outside the APAs (N = 53, total length 281–445 mm (mean = 357 mm)) (Table 1).
Upon capture, fish were landed as quickly as possible either using a rubberized net (angled fish) or by hand (hoop net). All fish were measured and placed in plastic coolers filled with lake water (45–95 L). Any fish that were deeply hooked, bleeding, or demonstrating abnormal or impaired behaviours (e.g., disequilibrium) were excluded from the study and released. Fish were captured via both methods concurrently, in similar habitat types, and, when applicable, using the same plastic baits. Upon capture, each fish was marked via clipping the tips off of one or more of the spines on the dorsal fin to indicate their area of capture and allow individual identification. Fish were then transported via boat to holding facilities at the Queen’s University Biological Station.