Size-selective harvesting is assumed to alter life histories of exploited fish populations, thereby negatively affecting population productivity, recovery, and yield. However, demonstrating that fisheries-induced phenotypic changes in the wild are at least partly genetically determined has proved notoriously difficult. Moreover, the population-level consequences of fisheries-induced evolution are still being controversially discussed. Using an experimental approach, we found that five generations of size-selective harvesting altered the life histories and behavior, but not the metabolic rate, of wild-origin zebrafish (Danio rerio). Fish adapted to high positively size selective fishing pressure invested more in reproduction, reached a smaller adult body size, and were less explorative and bold. Phenotypic changes seemed subtle but were accompanied by genetic changes in functional loci. Thus, our results provided unambiguous evidence for rapid, harvest-induced phenotypic and evolutionary change when harvesting is intensive and size selective. According to a life-history model, the observed life-history changes elevated population growth rate in harvested conditions, but slowed population recovery under a simulated moratorium. Hence, the evolutionary legacy of size-selective harvesting includes populations that are productive under exploited conditions, but selectively disadvantaged to cope with natural selection pressures that often favor large body size.

Recreational fisheries surveys are limited in time and place in many countries. This lack of data limits scientific understanding and sustainable management. Smartphone applications (apps) allow anglers to record the details of their fishing trips and catches. In this study, we describe the opportunities and challenges associated with angler apps as a source of recreational fisheries data, and propose minimum standards for data collection via angler apps. Angler apps are a potentially valuable source of conventional and novel data that are both frequent and extensive, and an opportunity to engage anglers through data sharing and citizen science. Realizing this potential requires that we address significant challenges related to angler recruitment and retention, data quality and bias, and integration with existing fisheries programmes. We propose solutions to each of these challenges. Given that the angler app market is diverse, competitive and unpredictable, we emphasize minimum standards for data collection as a way to ensure large and reliable data sets that can be compared and integrated across apps. These standards relate to trips and catches, and angler demographics and behaviour, and should be supported through consultation and research. Angler apps have the potential to fundamentally change how anglers interact with the resource and with management.

Degree-days (DD) are an increasingly popular method for explaining variation in fish growth and development. By including a base temperature (T o ) the DD formula limits calculations to temperatures that are relevant to growth. However, our review of growth studies shows multiple T o values in use for a given fish species. To determine how T o affects the ability of DD to explain within-population growth variation, we first show that the ability of DD to describe a growing season is robust to low values of T o . We then analyze immature length data from eight species and 85 water bodies in North America to show that there is a broad range of T o values that effectively explain growth variation. Based on these results, we argue that precise T o estimates are unwarranted for most single-population studies and recommend standard T o values (0, 5, 10, 15°C). Standardization facilitates comparative studies and promotes the use of DD in future research. To this end, we provide equations for converting annual DD at a given T o to annual DD at a standard T o . Résumé :Les degrés-jours (DJ) constituent une méthode de plus en plus usitée pour expliquer les variations associées à la croissance et au développement des poissons. L'incorporation d'une température de base (T o ) dans la formule des DJ limite les calculs aux températures pertinentes pour la croissance. Un examen des études sur la croissance indique toutefois que de multiples valeurs de T o sont utilisées pour des espèces de poissons données. Afin de déterminer l'incidence de T o sur l'adéquation des DJ pour expliquer les variations de croissance au sein d'une population, nous démontrons d'abord l'adéquation des DJ pour décrire une période de croissance jusqu'à de faibles valeurs de T o . Nous analysons ensuite des données sur la longueur de poissons immatures pour huit espèces et 85 plans d'eau en Amérique du Nord pour démontrer qu'il existe une grande fourchette de valeurs de T o qui permettent d'expliquer adéquatement les variations de croissance. À la lumière de ces résultats, nous postulons que des estimations précises de T o ne sont pas nécessaires pour la plupart des études sur des populations individuelles et recommandons l'utilisation de valeurs de T o normalisées (0, 5, 10, 15°C). Une telle normalisation facilite les études comparatives et favorisera l'utilisation de DJ dans des travaux futurs. Nous présentons à cet effet des équations pour la conversion de DJ annuels pour une T o quelconque en DJ annuels pour une T o normalisée. [Traduit par la Rédaction]