Decline in Longnose Gar Growth Following Reservoir Aging: Evidence from Back-Calculated Lengths in Tuttle Creek Reservoir

Longnose gar (Lepisosteus osseus) are characterized by exceptionally rapid growth rates, yet few studies have examined how changing environmental conditions influence their growth over time. We evaluated the hypothesis that reservoir aging would reduce longnose gar growth rates in Tuttle Creek Reservoir, Kansas, by comparing back-calculated lengths-at-age from fish collected in 1969 (7 years post-impoundment) and 2025 (63 years post-impoundment). Using branchiostegal rays, we aged 26 individuals and applied the Fraser-Lee method to back-calculate length-at-age. Back-calculated lengths were consistently lower in 2025 than 1969 for ages 3-9, with mean differences per age ranging from 50 to 143 mm. The largest difference was observed at age 7, when longnose gar in 1969 averaged 143 mm longer than those from 2025. These results support the hypothesis that trophic depression is associated with reservoir aging, where declining primary productivity and structural habitat degradation reduce growth rates over time. Reduced prey availability and increased interspecific competition from stocked predators may also contribute to slower growth. Overall, our findings indicate that reservoir aging might negatively impacts the growth rate of longnose gar, with potential cascading effects throughout the food web.