Modeling the population dynamics and sustainability of lake sturgeon in the Winnebago System, Wisconsin

The sustainability of exploited animal populations is increasingly a concern as species extinction rates accelerate due to the impact of human activities on the environment. Sturgeon are a group of large-sized, long-lived and late-maturing periodic-strategist anadromous and freshwater fishes that over the last 100 years suffered excessive harvesting of adults primarily for their prized caviar, and consequently, are now seriously threatened throughout their holarctic range. To achieve recovery and effective management of sturgeon, their population dynamics must be clearly understood.;I used 60 years of data, bomb radiocarbon dating, and a series of fisheries models including a statistical catch at age analysis of lake sturgeon ( Acipenser fulvescens) from the Winnebago System in east central Wisconsin, USA, to validate age estimates, define age and growth, weight-length relationships, size and age at maturity, fecundity, eggs per recruit, recruitment, mortality rates, abundance and yield per recruit. Age estimates of pectoral fin spines underestimated true age after age 14 defined by the power function True Age = Estimated Age^1.054796.Frontal cross sections of the otoliths accurately estimated true age.;Growth of Winnebago lake sturgeon occurs in two growth stanzas with an inflexion point at 96 cm (total length), age 12, with dimorphic separation of length at age occurring between males and females at 131 cm, age 25. Weight-length relationships were also best defined in two growth stanzas with an inflexion point at 71 cm, and by sex and stage of sexual maturity.;The population of lake sturgeon of the Winnebago System exhibits a protracted maturation period with males reaching 50% maturity at 120 cm, age 20, and females at 139 cm, age 27. Mean fecundity was 445703 (12767 eggs/kg body weight) with weight the best predictor of fecundity. Mean recruitment during 1955-2007 was estimated at 9002 yearlings each year, although stock-recruitment exhibited a Ricker-style inverse relationship. Instantaneous natural mortality was estimated at 0.055, and total annual mortality at 8.8% during 1977-2007. Abundance of lake sturgeon increased fourfold during 1954-2007 in the Winnebago System, an intrinsic rate of increase of 0.049, likely reaching carrying capacity in the 1990s due to long-term management policies beginning in 1874, and increased non-point pollution during the 1960s-1980s.;Long term simulation modeling predicted Winnebago lake sturgeon maintain population robustness at or below an annual exploitation rate of 4.7%, but significantly decline at higher exploitation levels, and go extinct at 20% exploitation.