Summary
- While the use of aquatic protected areas that exclude angling might be considered an evolutionarily enlightened management approach to dealing with fisheries‐induced evolution (FIE), there is little empirical data on the effectiveness of this approach at maintaining the diversity of phenotypic traits within protected areas.
- In species with paternal care, including largemouth bass (Micropterus salmoides), active nest‐guarding and aggression towards potential brood predators by males may render these individuals particularly vulnerable to capture by angling because of increased propensity to attack fishing lures/bait near their nests. Relative levels of aggression by these males during the parental care period correlates with their vulnerability to angling year round. Selective removal of more aggressive individuals by anglers should drive population‐average phenotypes towards lower levels of aggression.
- To assess the effectiveness of protected areas at mitigating FIE, the parental care behaviours of wild, free‐swimming male bass were compared during the early nesting period for bass within and outside protected areas in a lake in eastern Ontario. Nesting males within long‐standing aquatic protected areas closed to fishing for >70 years were more aggressive towards bluegill sunfish (Lepomis macrochirus), a potential nest predator, and patrolled larger areas around their nests compared with bass outside of sanctuaries. Males within protected areas were also more likely to strike at artificial fishing lures and were more prone to capture during angling events.
- Collectively, the findings suggest that the establishment of protected areas may promote phenotypic diversity such as more attentive and vigorous parental care, relative to areas open to angling. The extent to which this phenomenon occurs in other species and systems is likely to depend on the reproductive strategies of fish and their spatial ecology compared with protected area boundaries, and habitat quality within protected areas.
Methodology
Study site and species
All work was conducted in Lake Opinicon at the Queen's University Biological Station in Elgin, ON (N 44° 33′ 56.0″, W76° 19′ 23.6″; Figure 1) between 3 and 6 May 2015. Opinicon is mesotrophic with a mean depth of ~2.8 m and an area of ~780 ha (Agbeti, Kingston, Smol, & Watters, 1997) with two long‐established fish sanctuaries where angling is prohibited year round. These were established in 1939 (Murphy Bay fish sanctuary, 83 ha) and 1945 (Darlings Bay fish sanctuary, 14.2 ha) by the Ontario Ministry of Natural Resources and Forestry (OMNRF, formerly Lands and Forests) specifically for the conservation of largemouth bass. Although the sanctuaries were initially implemented as a means of maintaining quality of the recreational fishery, over time it has had the potential to play a broader role in conservation by providing unaltered habitat for protected species. These sanctuaries are located approximately 6 km apart on the east (Murphy Bay) and west (Darlings Bay) ends of the lake, and both contain ideal largemouth bass nesting habitat. Both sanctuaries are located in ‘drowned land’ areas, which contain many immersed stumps and fallen tree trunks resulting from flooding from construction of the Rideau Canal during the late 1820s (Karst & Smol, 2000). Lake Opinicon has a relatively high burden of nest predators (Gravel & Cooke, 2009) composed primarily of bluegill (Lepomis macrochirus), pumpkinseed (Lepomis gibbosus), and rock bass (Ambloplites rupestris).
Sixty‐eight free‐swimming, nesting male largemouth bass (all >23 cm total length) were assayed for parental care behaviour: 17 fish were sampled in each of the two sanctuary areas and 34 were sampled outside the sanctuaries. Only males from nests with similar habitat characteristics were included (shallow areas <1 m depth, coarse woody structure, and high vegetation densities; Ahrenstorff et al., 2009; DeMille, 2010) to minimize any habitat‐mediated differences in behaviour. Although behaviour in fishes is strongly influenced by environmental conditions, including temperature (Lemons & Crawshaw, 1985) and predation pressure (Cooke, Weatherhead, Wahl, & Philipp, 2008), these factors did not differ significantly between the two sanctuaries, between the non‐sanctuary areas, or between the sanctuary and non‐sanctuary areas (all P > 0.05).
Experimental protocol
Snorkelling surveys were conducted to locate nesting males guarding newly spawned eggs (< 3 days old). The size of nesting males (total length) and their relative nesting success (ordinal ranking of the number of eggs in the nest from 1 (low) to 5 (high), after Philipp et al., 1997; Stein & Philipp, 2015) were estimated through visual assessments. Egg abundance in nests is positively associated with levels of aggression towards potential nest predators (Suski & Philipp, 2004) and nests with fewer eggs tend to have higher levels of abandonment (Zuckerman, Philipp, & Suski, 2014), so only males with mating success scores ≥3 were observed. Parental behaviour of the nesting males was assessed through four different assays by a snorkeller and all snorkellers (N = 4) received identical training in assessment methods before beginning the study (Stein, Claussen, Cooke, & Philipp, 2014).
The following three behavioural tests were completed before assessing angling vulnerability. First, the nest attentiveness of bass was observed for 3 min, with nest attentiveness considered as the proportion of time the male spent on the nest protecting its brood out of the entire 3 min. The fish was assigned a score of 0 when it was more than 1 m from the nest or a score of 1 when it was within 1 m of the nest at 20 s intervals (O'Connor, Gilmour, Arlinghaus, Van Der Kraak, & Cooke, 2009). The level of nest attentiveness was determined by dividing the total attentiveness score by the number of observations made (9). During this 3‐min period the number of potential predators (bluegill, pumpkinseed, rock bass) that came within 1 m of the nest was recorded and used as a measure of ambient predator density. The male was then presented with a model brood predator consisting of a resin‐coated photograph of a bluegill sunfish mounted on a plexiglass backing attached to a 1.5 m dowelling rod (Coleman, Gross, & Sargent, 1985; Suski, Svec, Ludden, Phelan, & Philipp, 2003). The model was presented at distances of 2 m, 1 m, 0.5 m and on the nest (0 m) for periods of 10 s each or until the nesting male ‘rushed’ (male swam quickly towards the model), ‘struck’ (male made physical contact with the model) or ‘yawned’ (male opened his mouth and flared his branchiostegal membranes) at the model (after O'Connor et al., 2009; Suski & Philipp, 2004). The furthest position of the model from the nest that elicited one of these behaviours by the male bass was recorded as the response distance. Third, a glass jar containing a small live bluegill was placed directly onto the nest for a 1‐min period, during which the cumulative number of the three aggressive behaviours directed at the bluegill was recorded as the number of aggressive attempts.