Spatiotemporal variation in Lake Sturgeon movement and habitat selection in Missouri river tributaries : implications for the management and recovery of populations at range margins
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Lake Sturgeon were nearly extirpated from Missouri by the 1970s leading the Missouri Department of Conservation (MDC) to list the species as endangered within the state. Recovery efforts commenced with the publication of the first edition of Missouri's Lake Sturgeon Recovery Plan in 1984. Since, growing populations of mature individuals have been documented; however, information gaps regarding habitat selection and movement in the Missouri River Basin portion of its range hinder MDC's efforts to establish a self-sustaining population. In this project we focused on the following research objectives: (1) elucidate the factors that influence movement patterns of Missouri River Lake Sturgeon, (2) investigate survival and dispersal of stocked age-0 Lake Sturgeon from four stocking locations, (3) define seasonal habitat selection in multiple life stages of Lake Sturgeon and illustrate spatial availability of suitable habitats across the study area. I monitored movements 96 subadult and adult Lake Sturgeon over 3.5 years and 187 age-0 juvenile Lake Sturgeon during the fall/winter of two years. Missouri River tributaries were important habitats for adult and subadult Lake Sturgeon throughout the year. Lake Sturgeon use of the Osage River was greater in all months compared to the Gasconade River. Use of the Osage River was highest in the summer and lowest in the winter, and in the Gasconade River it was lowest in the summer and highest in the spring. In each month tributary occupancy was > 70 %. Spring upstream migrations occurred in each tributary and were correlated with above average discharges and temperatures from 13 to 19 [degrees]C. Fall migrations only occurred in the Osage River but were also correlated with intermediate temperatures and above-average discharges. A few individuals were detected as far upstream as Bagnell Dam at river km (rkm) 129 in the Osage River or rkm 241 in the Gasconade River. In the summer and winter, tributary habitat use for [approximately] 95 % of Lake Sturgeon was restricted to three reaches of deep pool habitat in the Osage and Gasconade rivers which may serve as thermal refugia. Spawning was not documented in either river, although some aggregations of Lake Sturgeon were observed around rocky shoals during the spring in the Osage River from rkm 50 to 80. Upstream migration distance was variable among individuals and years in the Gasconade River precluding the identification of potential spawning sites. Habitat selection was relatively similar in both tributaries and driven by selection for deep habitats > 7 m in all seasons. Suitability models suggest that preferred summer and winter deep water refugia may be limited to < 5 % of the mapped portions of each tributary but that preferred depth and coarse substrate for reproduction is relatively common at > 32 % of tributaries. Dispersal directions and distance for age-0 Lake Sturgeon differed among the four stocking sites. Individuals stocked at upstream sites mainly dispersed downstream to overwinter in similar locations as individuals stocked at downstream sites from rkm 10 to 50. Overwinter survival rates were estimated from 40-55 % and were not significantly different among stocking sites. Age-0 Lake Sturgeon selected shallower depths than adults or subadults in both rivers and slightly swifter current velocities in the Gasconade River. Habitat suitability models for the juveniles were able to predict age-0 habitat use and suggest that the greatest availability of nursery habitat occurs in the lower 11 km of the Osage River or in the reach from rkm 9 to 18 in the Gasconade River. These results can be used to inform management decisions designed to meet restoration objectives for Lake Sturgeon in Missouri and across its southern range margins such as: Managing hydrology of regulated rivers, protecting fish when they are vulnerable to harvest or injury in seasonal refugia, promoting resilience under shifting thermal and hydrologic regimes due to climate change, revealing sampling locations for population monitoring or spawning validation, allocating future stocking to suitable habitats, and directing habitat restoration and protection efforts.