Abstract
In 1954, brown trout were introduced to the Kerguelen archipelago (49°S, 70°E), a pristine, sub-Antarctic environment previously devoid of native freshwater fishes. Trout began spreading rapidly via coastal waters to colonize adjacent watersheds, however, recent and unexpectedly the spread has slowed. To better understand the ecology of the brown trout here, and why their expansion has slowed, we documented the marine habitat use, foraging ecology, and environmental conditions experienced over one year by 50 acoustically tagged individuals at the colonization front. Trout mainly utilized the marine habitat proximate to their tagging site, ranging no further than 7 km and not entering any uncolonized watersheds. Nutritional indicators showed that trout were in good condition at the time of tagging. Stomach contents and isotope signatures in muscle of additional trout revealed a diet of amphipods (68%), fish (23%), isopods (6%), and zooplankton (6%). The small migration distances observed, presence of suitable habitat, and rich local foraging opportunities suggest that trout can achieve their resource needs close to their home rivers. This may explain why the expansion of brown trout at Kerguelen has slowed.
Highlights
The introduction of exotic species into novel landscapes, both deliberately and unintentionally, is a major biodiversity and ecological concern[1,2,3]
Initial colonization success and subsequent spread of the brown trout at Kerguelen was attributed to anadromy, which allowed introduced populations access to the sea and its higher levels of food production
Physiological biopsies and dietary information, we aim to reveal the possible factors that may explain the unexpected decrease in brown trout colonization rates
Summary
The introduction of exotic species into novel landscapes, both deliberately and unintentionally, is a major biodiversity and ecological concern[1,2,3]. Iteroparous species, the ability of brown trout to make more than one sea feeding migration may be condition-dependent[25,28] Factors such as individual body length, sex, and nutritional state are known to influence the spatiotemporal aspects of marine habitat u se[27]. Not all introductions in the sub-Antarctic have succeeded (e.g. Marion Island), despite the environments being mostly free from the anthropogenic stressors that limit salmonids in other parts of their natural range (e.g. fishing pressure, habitat destruction, pollution, warming river temperature, etc.). Most sub-Antarctic rivers are naturally fishless, and so interspecific competition is limited or absent These characteristics make sub-Antarctic rivers excellent model systems in which to examine the factors that promote or impede the successful colonization of natural ecosystems by exotic species such as brown trout
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