Impact of Non-Native Salmonids on Fish Communities after Barrier Removal in Great Lakes Tributaries

Dam removal on Great Lakes tributaries may open headwaters to colonization by non-native salmonids.  The effects of these introductions on resident stream communities, specifically native coldwater fish communities, are unclear but should be determined to mitigate potential negative impacts.  The objective of this study was to determine differences and the rate of change in fish species composition above and below removed barriers to non-native salmonids. Four northern Michigan streams were sampled ranging from 0-5 years after barrier removal. Within three years of barrier removal relative abundance of non-native salmonids increased from 0% to nearly 20% in the upstream reaches while downstream reaches remained around 28%.  Relative abundance of native brook trout decreased from 100% of total salmonids to 44.1% in upstream reaches invaded by non-native salmonids. These findings illustrate that invasions from non-native salmonids via barrier removal can alter the structure of fish communities and lead to a decline in native brook trout populations rapidly. This information should be considered when prioritizing rivers in which dam removal is considered as a management tool to restore ecosystem connectivity.