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The impact of an introduced predator on a threatened galaxiid fish is reduced by the availability of complex habitats


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Stuart-Smith, RD, Stuart-Smith, JF, White, RWG and Barmuta, LA 2007 , 'The impact of an introduced predator on a threatened galaxiid fish is reduced by the availability of complex habitats' , Freshwater Biology, vol. 52, no. 8 , pp. 1555-1563 , doi: 10.1111/j.1365-2427.2007.01787.x.

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1. The availability of complex habitats such as macrophytes may be vital in determining
the outcomes of interactions between introduced predators and native prey. Introduced
brown trout (Salmo trutta) have impacted numerous small native freshwater fishes in the
southern hemisphere, but the potential role of complex habitats in determining the direct
outcomes of brown trout - native fish interactions has not been experimentally evaluated.
2. An in-lake enclosure experiment was used to evaluate the importance of structurally
complex habitats in affecting the direct impacts of brown trout on a threatened galaxiid
fish. Five Galaxias auratus and a single brown trout were added to enclosures containing
one of three different habitat types (artificial macrophytes, rocks and bare silt substrate).
The experiment also had control enclosures without brown trout. Habitat-dependence of
predation risk was assessed by analysis of G. auratus losses to predation, and stomach
contents of remaining fish were analysed to determine if brown trout directly affect the
feeding of G. auratus and whether this is also habitat-dependent.
3. Predation risk of G. auratus differed significantly between habitat types, with the highest
mortality in enclosures with only bare silt substrate and the lowest in enclosures
containing artificial macrophytes. This result highlights the importance of availability of
complex habitats for trout - native fish interactions and suggests that increasing habitat
degradation and loss in fresh waters may exacerbate the direct impacts of introduced
4. Stomach contents analyses were restricted to fish in enclosures with artificial
macrophytes and rocks, as most fish were consumed in enclosures with brown trout and
only bare silt substrate. These analyses suggest that brown trout do not directly affect the
feeding of G. auratus in complex habitats, but it is still unknown whether its feeding is
reduced if complex habitats are unavailable.

Item Type: Article
Authors/Creators:Stuart-Smith, RD and Stuart-Smith, JF and White, RWG and Barmuta, LA
Keywords: brown trout, enclosures, Galaxias auratus, macrophytes, predation risk
Journal or Publication Title: Freshwater Biology
ISSN: 0046-5070
DOI / ID Number: 10.1111/j.1365-2427.2007.01787.x
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