Recruitment, growth, and exploitation as determinants of brook trout size structure in natural lakes

Recreational fisheries are globally significant both culturally and economically, yet unmanaged harvest can erode population structure and sustainability. This study evaluates the long-term effectiveness of a trait-informed harvest regulation combining reduced daily bag limits with weight-based harvest caps on brook trout (Salvelinus fontinalis) populations in eight unstocked, oligotrophic lakes in Newfoundland, Canada. Over 15 years (1994–2008), standardized index netting and winter creel surveys were used to assess changes in fish size structure and angler behaviour. Mixed-effects models revealed significant increases in maximum length (L_max), mean length at capture (L_c), and proportional size distribution (PSD) following regulation implementation, with no significant changes in catch rate, effort, or release rate. We applied a variance partitioning framework to identify mechanisms driving PSD improvements, attributing 31 % of PSD variation to growth, 18 % to recruitment, and 7 % to exploitation. These findings demonstrate that biologically grounded regulations can enhance fishery quality while maintaining angler engagement. The study offers one of the first empirical demonstrations of PSD driver partitioning in a wild brook trout fishery. It provides evidence to support adaptive, trait-informed management in recreational salmonid systems.