Influence of a Minimum‐Length Limit Regulation on Wild Brown Trout: an Example of Recruitment and Growth Overfishing

Abstract

The relative abundance of the largest size‐classes of individuals within a fish population has an important influence on recruitment success. Fishing regulations with a basis in size (e.g., minimum‐length limits) can directly impact the abundance of these larger individuals and thus potentially influence recruitment. We analyzed whether recruitment of exploited native Brown Trout Salmo trutta populations was affected via the extraction of large individuals (>220 mm, i.e., minimum‐length limit). The study was replicated temporally (2007–2009) and spatially across seven recreational fishing sections (four exploited and three catch‐and‐release sections) within the River Tormes located in central Spain. Catch‐and‐release sections were used as reference points to compare with exploited sections. We tested the hypothesis that minimum‐length limit regulations would adversely affect fish recruitment through fishing‐induced mortality of large individuals. Spawning stock (measured as fish >220 mm) and young‐of‐the‐year abundances were estimated using multiple‐pass depletion methods. We modeled the relationship between spawning stock and subsequent recruitment using a nonparametric approach (generalized additive models) to fit the best stock–recruit relationship. Additionally, von Bertalanffy growth and yield‐per‐recruit models were generated to evaluate the potential for growth and recruitment overfishing. The restrictive length limits used to regulate harvest in the study area limited both recruitment and adult abundance. The present study provides evidence that the use of minimum‐length limit regulations in the management of recreational fisheries has the potential to adversely affect the species’ recruitment. Such adverse impacts could be occurring via both recruitment overfishing and growth overfishing, exemplifying that the removal of the larger size‐classes of individuals through recreational fishing could have important consequences for recruitment. Management actions should be directed to protect large individuals (e.g., via harvest slots) rather than promote their removal, thereby reducing the chances of overfishing. Received November 25, 2015; accepted April 18, 2016Published online August 24, 2016

Standard Assessments Reveal Context‐Dependent Responses of Crappie Populations to a Length‐Based Regulation in Ohio Reservoirs

“…Concentrating harvest on large individuals has been shown to cause recruitment overfishing in salmonids by removing the individuals that contribute the greatest reproductive output (Sánchez‐Hernández et al. ). Given density‐dependent control on growth and increasing fecundity and egg quality with increasing female length (Bunnell et al.…”

“…reproductive investment and reductions in recruitment (Bunnell et al 2006;Michaletz 2013). Concentrating harvest on large individuals has been shown to cause recruitment overfishing in salmonids by removing the individuals that contribute the greatest reproductive output (Sánchez-Hernández et al 2016). Given density-dependent control on growth and increasing fecundity and egg quality with increasing female length (Bunnell et al 2005), there is potential for length-based regulations to similarly influence crappie recruitment dynamics.…”

“…; Sánchez‐Hernández et al. ). Fisheries managers must therefore understand the effects of MLLs on fish populations to evaluate the success of these regulations for producing desired population outcomes.…”

“…Length-based regulations, including minimum length limits (MLLs), are often implemented in highly exploited fisheries to allow fish to grow to larger sizes before harvest and increase yield (Isermann and Paukert 2010). Although MLLs have successfully achieved these objectives in some inland recreational fisheries (e.g., Oele et al 2016), they may also be counterproductive and lead to density-dependent slow growth and recruitment overfishing (Gwinn et al 2015;Sánchez-Hernández et al 2016). Fisheries managers must therefore understand the effects of MLLs on fish populations to evaluate the success of these regulations for producing desired population outcomes.…”

Recreational Fisheries: The Need for Sustainability in Fisheries Management of Alpine Rivers

“…In other words, changing environmental conditions entail changing population densities. However, historically overexploitation has repeatedly occurred when management practices are tied to habits or routines rather than regular environmental updates (e.g., Sánchez-Hernández et al 2016). Consequently, exploitation of natural resources such as wild fish stocks requires a constant reconsideration of what an ecosystem under current conditions is able to yield (Fig.…”