Steelhead return rates and relative costs: A synthesis of three long-term stocking programs in two Minnesota tributaries of Lake Superior

Abstract

Hatchery augmentation of steelhead Oncorhynchus mykiss was evaluated over 20years in Minnesota tributaries of Lake Superior using three approaches — stocking fry or yearlings of a naturalized strain (STT), and yearlings of a domesticated strain (KAM). The STT strain was introduced over 100years ago and became naturalized to Lake Superior and its tributaries, unlike KAM, which has not been shown to reproduce successfully in streams. We compared smolt–adult return rates to anglers and in-river traps, and production costs per adult for these three programs in the French and Knife rivers. STT smolts derived from stocked fry in the French River resulted in the highest smolt–adult return rates to traps and anglers (13.3%), and lowest cost per returning adult ($46). STT stocked as yearling smolts produced the lowest return rate (1.5%) and highest cost per returning adult ($192) for both rivers combined. KAM stocked as yearling smolts were intermediate in return rate (2.6%) and cost per adult ($90). Differences in return rates of the three strains were attributable to the extent of domestication selection, size at stocking, season of stocking, and summer lake temperatures. Smolts derived from fry-stocked STT were strongly influenced by summer lake temperatures in their first lake year. Yearling-stocked STT were influenced by size at stocking and summer lake temperatures. KAM yearlings benefitted from summer stocking at larger sizes. Based on poor survival and fiscal constraints, the STT yearling program was discontinued. Stocking programs will continue to evolve according to changing biological, financial, social, and political pressures.