Trophic Economics of Lake Trout Management in Reservoirs of Differing Productivity

• Published in: North American journal of fisheries management 2000-02, Vol.20 (1), p.127-143
• Main Authors: Johnson, Brett M., Martinez, Patrick J.
• Format: Article
• Language: English
• Subjects: Freshwater; Oncorhynchus; Oncorhynchus mykiss; Oncorhynchus nerka; Salvelinus namaycush
• ISSN: 0275-5947; 1548-8675
• DOI: 10.1577/1548-8675(2000)020<0127:TEOLTM>2.0.CO;2

Because of their potential to reach large size, lake trout Salvelinus namaycush are managed as trophy fish in many reservoirs in the western United States. In Colorado, restrictive harvest regulations for lake trout were enacted in reservoirs exhibiting a range of productivities. Annual stockings of kokanee (lacustrine sockeye salmon Oncorhynchus nerka) and rainbow trout O. mykiss sustained sport fisheries, but stocked fish also dominated the prey fish assemblages in these systems. Hydroacoustic surveys suggested that lake trout management allowed an imbalance to develop between prey fish biomass and the biomass of piscivorous lake trout. Piscivorous fish biomass was, on average, 60% of total pelagic fish biomass. Bioenergetics modeling confirmed the imbalance: annual lake trout consumption was near or exceeded annual pelagic prey fish supply (standing stock plus production); the degree of imbalance was greater in less productive reservoirs. Annual subsidies to the food web, in the form of stocked sport fish, were necessary to allow the imbalance between predator and prey populations to persist, especially in the least‐productive systems. Though highly sensitive to the size at which hatchery fish are consumed, the per capita costs to sustain lake trout growth at observed levels would total about US$200 per lake trout in the more productive reservoirs and $300–600 per lake trout in the less productive reservoirs. The cost of maintaining high lake trout biomass in these stocked systems may be a difficult management strategy to justify and sustain, either economically or socially.