Factors Affecting the Vulnerability to Angling of Nesting Male Largemouth and Smallmouth Bass

—Some, but not all, jurisdictions in North America have regulations in place designed to protect nesting male largemouth bass Micropterus salmoides and smallmouth bass M. dolomieu from angling. The underlying assumption that brood-guarding males are particularly vulnerable to angling, however, is untested. In this study, we quantified the vulnerability of brood-guarding largemouth bass and smallmouth bass to angling and determined the factors that influenced that vulnerability. For this, male largemouth bass and smallmouth bass guarding newly spawned eggs were located by snorkel survey. The aggression of these males towards a brood predator was quantified, the male’s susceptibility to angling lures was assessed, and the quantity of eggs in his nest and his size were recorded. Male largemouth and smallmouth bass were quite vulnerable to angling while guarding their nests, 70% of nesting male smallmouth bass and 54% of nesting male largemouth bass being hooked during the experimental angling trials. The level of aggression shown by nesting males of both species towards the brood predator model was significantly influenced by the quantity of eggs in his nest. This relationship was true regardless of male size, although larger males of both species typically received a greater quantity of eggs during a reproductive attempt. Furthermore, vulnerability to angling correlated positively with the quantity of eggs in a male’s nest. Thus, the males that had the largest broods and the greatest potential to contribute to annual recruitment were the most likely to be caught by anglers, indicating that angling for nesting bass during the brood-guarding period has the potential to negatively impact bass populations. Largemouth bass Micropterus salmoides and smallmouth bass M. dolomieu are two of the most popular and economically important sport fish in North America (Department of Fisheries and Oceans Canada 1998; Pullis and Laughland 1999). In response, management agencies have implemented numerous regulations to protect and enhance bass fisheries (e.g., daily harvest limits, length limits, and closed areas; Noble and Jones 1999; Noble 2002). These regulations are often effective in preventing overexploitation (Sztramko 1985; Wilde 1997). In some jurisdictions, seasonal closures during the brood-guarding period, when bass may be most vulnerable to angling, are added to provide additional protection (Quinn 2002). Like other centrarchids, male largemouth bass and smallmouth bass excavate shallow, bowl-like nests in the littoral zones of lakes and rivers, typically in late spring (Breder 1936; Coble 1975; Heidinger 1975). Following nest construction, females are courted to the nest site, and once spawn* Corresponding author: [email protected] Received April 25, 2003; accepted March 4, 2004 ing is completed, the male remains alone at the nest site to provide sole parental care for the developing brood (Breder 1936; Coble 1975; Heidinger 1975). Parental care can last up to 5 weeks and includes both fanning the nest to provide oxygen to the eggs and larvae (Coble 1975; Heidinger 1975; Ridgway 1988) and defense against predators (Ridgway 1988; Ongarato and Snucins 1993; Suski et al. 2003). Defense of a brood can occur in many forms, and Breder (1936) documented that in centrarchids, brood defense can occur in the form of ‘‘yawning’’ displays as well as through chasing potential intruders from the nest area. If a nesting male largemouth bass or male smallmouth bass is removed from his nest through angling, his brood is left defenseless against predators during his absence (Neves 1975). If that male is harvested, rapid and total brood loss is a likely outcome. If the male is released, variable levels of brood loss are possible, depending upon the conditions of release (Philipp et al. 1997). Reduction in brood size by predation while a male is absent from his nest increases the likelihood of premature abandonment (Suski et al. 2003) and may result 1101 VULNERABILITY OF NESTING BASS TO ANGLING in zero reproductive output for that spawning event. Following the return of the male to the nest, the physiological impairment that accompanies a catch-and-release angling event can reduce the level of defense provided to the brood (Kieffer et al. 1995; Cooke et al. 2000; Suski et al. 2003). Regulations closing bass fisheries during spawning season are promulgated under the assumption that bass are more vulnerable to angling during this stage, but this assumption has not been validated (but see Shuter et al. 1980; Philipp et al. 1997; Suski et al. 2003). In this study, we quantified the vulnerability to angling of nesting male largemouth bass and smallmouth bass and determined which factors affect this vulnerability. We also examined the interrelationships among four different characteristics of brood-guarding male largemouth bass and smallmouth bass: total length (TL), mating success, aggression toward brood predators, and vulnerability to angling.