Viability of a Brook Trout Source Population Used for Egg Collection in Wisconsin's Wild Trout Stocking Program

We evaluated the ability of a wild brook trout population to serve as a long-term source of eggs for Wisconsin’s wild trout stocking program. We surveyed Ash Creek in spring and autumn 2004-2012 to obtain demographic data for brook trout comprising two strata: in-stream spawners and those removed for 6-8 weeks for in-hatchery spawning. The annual apparent survival rate was 0.15 and we detected no significant difference in survival between in-stream and in-hatchery spawners. Annual variability in abundance, size structure, and average fecundity resulted in variable potential egg production, which varied from 73,000 to 519,000 eggs per year and affected our ability to meet propagation objectives. The percentage of brook trout removed for egg collection ranged from 32% to 84% of female spawners. Recruitment, however, did not vary as a function of egg production. Recruitment was likely limited by flooding events and an increasing population of brown trout. Brown trout had been annually suppressed by removal until fish transfer protocols changed in 2007 following the discovery of viral hemorrhagic septicemia in Wisconsin lakes. We discuss current risks to the wild trout stocking program and management options for ensuring program viability.