Goldeye (Hiodon alosoides) population dynamics in Lake Oahe and Lake Sharpe, South Dakota

Goldeye are a species of hiodontid native to northern North America. In the Missouri River reservoirs of South Dakota, Lake Oahe and Lake Sharpe, goldeye populations have been documented as bycatch during standardized surveys with limited attention given to their long-term abundance patterns or role in the fishery. However, in recent years, noticeable declines in goldeye abundance have led to investigating the current population status along with what factors could be influencing goldeye densities. We sought to examine relative abundance trends from 2014 to 2023 and describe current population dynamics (i.e., size structure, relative weight (W_r), age, growth, and mortality) of these two Missouri River mainstem reservoirs. In Lake Oahe, the median total length of sampled goldeye was 372 mm (minimum = 274 mm; maximum = 474 mm) with an estimated observed maximum age of 7. In Lake Sharpe, the median total length of sampled goldeye was 392 mm (minimum = 284; maximum = 435 mm) with an estimated observed maximum age of 5. Goldeye W_r averaged 104 in Lake Oahe and 96 in Lake Sharpe indicating good body condition. We fit von Bertalanffy growth models to back-calculated length at annulus formation for both Lake Oahe (L_∞ = 482 mm, K = 0.18, and t₀ = − 2.96) and Lake Sharpe (L_∞ = 430 mm, K = 0.27, and t₀ = − 2.69) to evaluate goldeye growth. Lake Oahe estimated annual mortality was 27.2%. We fit GLMs and used AICc to evaluate the relationship between goldeye CPE and lake elevation, growing degree days (GDD), and predator CPE and found weak relationships between goldeye abundance and lake elevation and GDD in the first study to attempt to examine relationships between goldeye abundance and environmental variables potentially impacting dynamic rate functions. Our work highlights the paucity of basic life history information for goldeye and the lack of harvest regulations across its native range.