Spatiotemporal variation in Lake Sturgeon movement and habitat selection in Missouri river tributaries : implications for the management and recovery of populations at range margins

Abstract

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 [greater than] 70 [percent]. 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 [percent] 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 [greater than] 7 m in all seasons. Suitability models suggest that preferred summer and winter deep water refugia may be limited to [less than] 5 [percent] of the mapped portions of each tributary but that preferred depth and coarse substrate for reproduction is relatively common at [greater than] 32 [percent] 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 [percent] 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.

Habitat selection in a southern Lake Sturgeon population: implications of temporal, spatial, and ontogenetic variation for restoration

“…Similarly, there was greater macroinvertebrate production and Lake Sturgeon use of major tributary confluences in the Mississippi River and Hudson Bay drainages (Chiasson et al 1997; Knights et al 2002). Although we did not track the 6–18% of age‐0s that exited tributaries during the fall to winter study period (Moore 2021 a ), the channelized mainstem Missouri River contains current velocities exceeding 1 m/s that may not be suitable for juvenile sturgeon (Jacobson & Galat 2006). Survival of stocked fingerlings in these rivers was estimated to be approximately 50% (Moore 2021 a ), which is higher than other populations and implies that sufficient suitable nursery habitat may exist.…”

“…Setlines were equipped with 8/0 Shaughnessy non‐offset hooks and baited with nightcrawlers and gillnets were set parallel to the current and were 2.5–3.5 m high with 101–152 mm bar mesh. We implanted Vemco V16‐4H (Halifax, Nova Scotia, Canada) acoustic transmitters (1540‐day battery life) into the abdominal cavity of 97 adult and subadult Lake Sturgeon (mean 1,119 mm fork length [FL], range 737–1,510 mm FL), 63 in the Osage, and 34 in the Gasconade river (Moore 2021 a ). Incisions were sealed with three to four interrupted sutures.…”

“…2). We attempted to manually locate all individuals occupying a tributary once a month using directional hydrophones and the ground-zero method (positional accuracy <30 m) from May 2017 to May 2020 (Holland et al 1992;Moore 2021a). Tracking for age-0 habitat selection focused on the Osage River from October 2018 to February 2019, and the Gasconade River from October 2019 to February 2020.…”

“…However, natural reproduction has not yet been documented in the Missouri River basin and hydrologic regulation, channelization, and climate change are persistent threats. Adult and subadult Lake Sturgeon spend over 70% of the time primarily in short reaches of two Missouri River tributaries and most juveniles exhibit overwinter fidelity to stocking tributaries (Moore 2021 a ). However, the habitat factors explaining these movement patterns have not been explored.…”

“…Habitat limitations during key life history events, such as spawning, overwintering, foraging, or resting, may be recovery bottlenecks. As a result, Missouri's Lake Sturgeon Recovery Plan prioritized understanding Lake Sturgeon habitat requirements to guide habitat remediation, hydrologic management, barrier passage facilitation, and stocking site selection (Moore 2021 b ).…”