Present address: Graduate School of Environment and Information Sciences, Yokohama National University, Hodogaya-ku, Yokohama 240–8501, Japan.
The impact of exotic trout on native charr in a Japanese stream
Article first published online: 30 SEP 2004
Journal of Applied Ecology
Volume 41, Issue 5, pages 962–972, October 2004
How to Cite
MORITA, K., TSUBOI, J.-I. and MATSUDA, H. (2004), The impact of exotic trout on native charr in a Japanese stream. Journal of Applied Ecology, 41: 962–972. doi: 10.1111/j.0021-8901.2004.00927.x
- Issue published online: 30 SEP 2004
- Article first published online: 30 SEP 2004
- Received 10 November 2003; final copy received 12 April 2004
- biological invasion;
- competition coefficient;
- habitat shift;
- ideal free distribution;
- introduced species;
- non-native trout
- 1Regression and isodar methods developed by community ecologists provide tools for evaluating the existence and magnitude of interspecific interactions in the field. In this study, we examined the usefulness of both methods to assess the impact of exotic trout on native charr.
- 2Brown trout Salmo trutta and rainbow trout Oncorhynchus mykiss have been introduced world-wide. They are invading many streams in Japan that also harbour native salmonids. We studied these species and the endemic Asian white-spotted charr Salvelinus leucomaenis in the Hekirichi River, south-western Hokkaido, Japan. We estimated the densities of all three species in pools and riffles from 27 stream reaches over 2 successive years. Data were analysed by regression and isodar methods to infer interspecific interactions.
- 3The regression method identified a negative relationship between brown trout and white-spotted charr densities, implying that brown trout are replacing white-spotted charr.
- 4The isodar method identified significant competition for habitat between rainbow trout and white-spotted charr. This method suggested that white-spotted charr preferred pools to riffles when rainbow trout were scarce but moved from pools to riffles as trout density in the pools increased.
- 5Synthesis and applications. Although they are based on limited data, regression and isodar methods were able to evaluate the potential impact of exotic trout on native white-spotted charr. From these results, we were able to hypothesize mechanisms of displacement of native charr by exotic trout. However, according to the two methods the mechanisms underlying the negative impacts on charr differ between brown and rainbow trout; in other words, limitations exist for both methods. From a more practical viewpoint, the analyses conducted in this study may be useful tools for conservation biologists who have limitations on their time and effort but must assess the impacts of exotics on native species.