Population Abundance of Spawning Lake Sturgeon in the St. Lawrence River

Abstract

The Lake Sturgeon Acipenser fulvescens is a large, long-lived freshwater fish that completes its entire lifecycle in freshwater, but migrates long distances. Human modifications to critical spawning habitats and migration corridors due to pollution and dams, coupled with high historical fishing mortality, have reduced most populations to all-time low abundances. In New York, USA, the species remains listed as threatened but recovery efforts including fishing moratoria, propagation and stocking, and habitat improvements have recovered 4 of the 7 remaining distinct population segments to interim targets for abundance. We assessed trends in Lake Sturgeon population abundance at two artificial spawning beds near Iroquois Dam for the aggregations on either side of the impassable barrier in the St. Lawrence River, North America. Fish were counted on 10 replicated video transects throughout the spawning season from 2011 through 2022 using underwater video. Counts of Lake Sturgeon in 30 m × 30 m grid cells along these transects were used to estimate population density at spawning beds upstream and downstream of the dam while accounting for imperfect detection within spatially explicit count models. Overall detection probability of the sturgeon was low (mean: 0.04, 95% CRI: 0.006-0.113) but was highest during the middle of the spawning season, reaching a maximum of 0.12 (0.10-0.13). Mean abundance was 10 (0-58) fish per 900 m2 at the downstream bed and 5 (0-30) at the upstream bed, with a mean difference of 5 (4-6) fish per 900 m2 across years. Periodicity in abundance was noted at the downstream bed. Abundance decreased slightly 2011-2023, with a mean population growth rate of -0.006 (-0.017 to -0.001) across beds. The approach we adopted for analysis could potentially be adapted to a wide range of data sources within Lake Sturgeon monitoring programs, particularly if combined with auxiliary demographic information. Future studies could improve understanding and interpretation of trends from these models with information regarding immigration and emigration from the study area and recruitment to this population segment.