Revista Chilena de Historia Natural 79 (1): 97-117, 2006
RESEARCH ARTICLE
Southern Chile, trout and salmon country: invasion patterns and threats for native
species
In order to evaluate the present distribution patterns of salmonids and their potential
effects on native fish, we sampled 11 large lakes and 105 streams, encompassing a total of 13 main hydrographic watersheds of
southern Chile (39° to 52° S). Overall, trout (Salmo trutta and Oncorhynchus mykiss) accounted for more
than 60 % of total fish abundance and more than 80 % of total biomass, while 40 % of the streams sampled did not have native fish.
Salmon, introduced for aquaculture, such as O. kisutch, Salmo salar, and O. tshawytscha, were
only present in lakes with salmon farming and did not seem to be reproducing naturally in affluent streams. We tested the effect of river
geographic origin (Andes mountains, central valley, or Coastal range) on fish abundance and found that rainbow trout was more
restricted to the Andean streams with higher water discharge, while brown trout was widely distributed and did not relate to any of
several catchment attributes measured. The abundance of native fish was greater in lakes than in streams and the highest native fish
biodiversity occurred in streams of the central valley. The most common native species were Galaxias maculatus,
G. platei, Brachygalaxias bullocki, Aplochiton zebra and Basilichthys australis. Streams with higher conductivity,
larger pool areas, more fine sediments, and low brown trout densities were more suitable for native fish. Thus, catchments with higher
anthropogenic disturbance appeared as refuges for native species. Given the descriptive nature of our study we can only presume the
negative impacts of trout and salmon on native fish; an effect which should be superimposed on biogeographical conditioning of
present distribution. Yet based on the present abundance and distribution patterns of salmonids and native fish, negative effects are
very likely. Conservation of native fish biodiversity in central valley streams, far from protected areas or national parks and fully exposed
to human perturbations represents a great challenge. We propose to enhance conservation by exerting a stronger sport fishing
pressure on trout in those streams.
Key words:
trout invasion, galaxid
fish, salmon farming, catchments characteristics
