Long-lived species from marine and freshwater environments have experienced declines linked to anthropogenic effects such as overexploitation, dam construction, and habitat modification. An understanding of the age structure and the associated dynamics determined from these data for long-lived species is critical for both perseverance of at-risk species and maintenance of exploited species. We used pallid sturgeon (Scaphirhynchus albus) to evaluate the efficacy of mark–recapture data from known-age, hatchery-reared fish (ages 1 to 7) to corroborate age and growth estimates obtained from sectioned pectoral fin rays. Accuracy of age estimates from known-age fish was 13%, whereas 72% of estimates were within 2 years of the true age. Annual growth was significantly different between estimated growth (back-calculated) and actual observations of tagged pallid sturgeon. Age for pallid sturgeon of any given size was estimated with parameters derived from mark–recapture data, and the predicted length-at-age relation was similar to observations from known individuals. In instances where age determination for all ages of interest cannot be verified, mark–recapture appears to be a viable solution for examining growth and has shown promise as a tool for estimating ages in long-lived species with calcified structures that are difficult to read.
We used mark-recapture data from shovelnose sturgeon (Scaphirhynchus platorynchus) to describe range-wide growth characteristics and developed a model to estimate ages. Data were solicited throughout much of the current distribution of shovelnose sturgeon, specifically from the mainstem Missouri and Mississippi rivers and their tributaries. Shovelnose sturgeon exhibited variable growth among locations; however, adult fish exhibited almost no growth after they reached a particular size, presumably the size at sexual maturity. Shovelnose sturgeon from the Mississippi River basin attained greater maximum sizes and ages compared with the Missouri River basin. However, two populations from the Mississippi River that received high exploitation from commercial harvest had truncated age distributions with smaller asymptotic lengths. Lower Missouri River populations were characteristic of exploited populations (i.e., smaller fish and reduced longevity), presumably a result of anthropogenic effects. Wide discrepancies in maximum age and size suggest shovelnose sturgeon are capable of displaying phenotypic plasticity in response to exploitation or environmental influences. Determining metapopulation dynamics is a priority because it is unknown how population connectivity may influence dynamic rate functions and persistence of large-river fishes. Identifying potential source-sink connections in terms of population dynamics may provide a template for direction of future restoration and recovery efforts.Résumé : Nous avons utilisé des données de marquage-recapture d'esturgeons scaphirhynques (Scaphirhynchus platorynchus) pour en décrire les caractéristiques de croissance sur l'ensemble de leur aire de répartition et élaborer un modèle pour estimer les âges. Des données ont été sollicitées dans la majeure partie de l'aire de répartition actuelle de l'espèce, plus précisément des bras principaux de la rivière Missouri et du fleuve Mississippi et leurs affluents. Si la croissance des esturgeons scaphirhynques varie selon la localité, les poissons adultes ne présentent presque aucune croissance après avoir atteint une taille donnée, vraisemblablement leur taille à maturité sexuelle. Les esturgeons scaphirhynques du bassin du Mississippi atteignent des tailles et des âges maximums supérieurs à ceux du bassin de la rivière Missouri. Cependant, deux populations du Mississippi faisant l'objet d'une forte exploitation commerciale présentent des distributions d'âges tronquées et des longueurs asymptotiques plus faibles. Les populations du cours inférieur de la rivière Missouri sont caractéristiques des populations exploitées (c.-à -d. poissons plus petits de longévité réduite), vraisemblablement le résultat d'effets d'origine humaine. De grandes divergences sur le plan de l'âge et de la taille maximums donnent à penser que les esturgeons scaphirhynques peuvent faire preuve de plasticité phénotypique en réaction à l'exploitation ou à des influences environnementales. La détermination de la dynamique des métapopulations constitue une prio...
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