Quantifying Predation on Galaxiids and Other Native Organisms by Introduced Rainbow Trout in an Ultraoligotrophic Lake in Northern Patagonia, Argentina: a Bioenergetics Modeling Approach

VIGLIANO, PABLO H.; BEAUCHAMP, DAVID A.; MILANO, DANIELA; MACCHI, PATRICIO J.; ALONSO, MARCELO F.; GARCÍA ASOREY , MARTÍN I.; DENEGRI, MARÍA A.; CIANCIO, JAVIER; LIPPOLT, GUSTAVO E.; RECHENCQ, MAGALÍ; BARRIGA, JUAN PABLO

Transaction of the American Fisheries Society

American Fisheries Society

Lugar: Grosvenor Lane, Bethesda; Año: 2009 vol. 138 p. 1405 - 1419

0002-8487

Exotic rainbow trout Oncorhynchus mykiss support an economically valuable recreational fishery in Patagonia, but also create concern for impacts on native organisms. These concerns are intensified by the possibility of hatchery release programs in this region. For Lake Moreno, Río Negro Province, Argentina, we estimated predation losses of different prey by rainbow trout, using a bioenergetics model combined with input data from directed sampling on growth, seasonal diet, distribution, and thermal experience. The fish community was sampled seasonally using gill nets, hydroacoustics, and ichthyoplankton nets. Pelagic galaxiid larvae followed by benthic juvenile and adult Galaxias maculatus were the most important components of the diet. Bioenergetic simulations showed that over a 6 year life span in the lake (age 1-7), rainbow trout attained a body mass of 2.3 kg and consumed 74.7 kg of food, of which 20% consisted of galaxiid larvae and 16% G. maculatus adults. Based on an estimated abundance of 29,000, age 1-7 rainbow trout, this predator exerted significant, but sustainable mortality on the native prey populations, consuming 44 MT, or an estimated 23% of the annual larval galaxiid production, and 35 MT of G. maculatus adults which represented an unknown fraction of the post-larval population. Galaxiids supported the estimated predation demand under current conditions. However, simulations of stocking strategies normally proposed for this region showed that consumption demands on prey would increase to unsustainable levels, reducing native fish populations and likely reducing growth of rainbow trout. It is also probable that the fish community composition would shift further in response to the increased demand for prey by stocked predators. This implies that, in some cases, stocking could jeopardize sport fisheries, and stocking strategies should be evaluated on a case-by-case basis to be consistent with specific objectives for native fish conservation and sustainable food web interactions.