Semi-natural streams

Non-native salmonids (% occurance).
Occurance from Stanfield et al. (2006).


When Atlantic salmon disappeared from Lake Ontario, non-native salmonids were stocked to provide a fishery and to control the increasing population of prey fishes. Millions of rainbow trout, brown trout, Chinook salmon, and coho salmon were stocked into Lake Ontario. All have established naturalized populations.

Atlantic salmon do not naturally co-occur with any of these non-native salmonids, thus Atlantic salmon may be exposed to greater interspecific competition than naturally encountered. Atlantic salmon may be competitively displaced by certain non-native salmonid species. Rainbow trout and brown trout, in particular, overlap in their resource preferences with Atlantic salmon and tend to be more aggressive than Atlantic salmon. In addition, Atlantic salmon populations vary in their competitive ability and certain populations may be better able to cope with competition with non-native salmonids.


This study will examine the performance of three candidate populations exposed to non-native salmonids in semi-natural streams. Juvenile performance will be determined using measures that are related to the survival of salmonids in natural streams.

Semi-natural stream.
Modified from Van Zwol (2011)
Semi-natural streams contain important features of the natural habitat. Two important features are water velocity and depth: in natural streams there are riffle (fast and shallow) and pool (slow and deep) microhabitats. Atlantic salmon prefer riffle microhabitats and upstream positions (first access to drifting food). If non-native salmonids are better competitors, they may displace Atlantic salmon out of the riffle to the pool microhabitat.

Juveniles (fry) of all species will be placed into semi-natural streams for 10 months. Salmonid species will be differentially tagged using sub-dermal coloured plastic (elastomer).

Semi-natural streams will contain one of three groups of fish:

  1. Pure Atlantic salmon: Atlantic salmon of one population
  2. Two-species: Atlantic salmon + one non-native salmonid species (either rainbow trout, brown trout, coho salmon, or Chinook salmon)
  3. Multi-species: Atlantic salmon + all four non-native salmonid species

The multi-species group is to examine whether the effects on Atlantic salmon are worse, better, or no different than expected from a simple additive function of the effects occurring in the two-species groups.

The traits measured during the experiment are:

  • Microhabitat use (monthly, measured with a camera)
  • Downstream displacement (monthly, measured with a camera)
  • Size and condition (monthly)
  • Circulating hormone concentrations (end of experiment)
  • Swim performance (end of experiment), collaboration with Dr. Pedro Peres-Neto
  • Gene expression and MHC genotype (end of experiment), collaboration with Dr. Daniel Heath


He X, Houde ALS, Neff BD, Heath DD. 2018. Transcriptome response of Atlantic salmon (Salmo salar) to competition with similar non-native species. Ecology and Evolution |PDF|

Smith AD, Houde ALS, Neff BD, Peres-Neto PR. 2017. Effects of competition on fitness-related traits. Oecologica 183: 701713. |PDF|

Houde ALS, Wilson CC, Neff BD. 2017. Performance of four salmonids species in competition with Atlantic salmon. Journal of Great Lakes Research 43: 211215. |PDF|

Houde ALS, Wilson CC, Neff BD. 2015. Effects of competition with four non-native salmonid species on Atlantic salmon from three populations. Transactions of the American Fisheries Society 144: 1081-1090. |PDF|

Houde ALS, Wilson CC, Neff BD. 2015. Predictability of multi-species competitive interactions in three populations of Atlantic salmon. Journal of Fish Biology 86: 1438-1443. |PDF|

Xiaoping H, Wilson CC, Wellband KW, Houde ALS, Neff BD, Heath DD. 2015. Transcriptional profiling of two Atlantic salmon strains: implications for reintroduction into Lake Ontario. Conservation Genetics 16: 277-287. |PDF|

Houde ALS, Wilson CC, Neff BD. 2015. Competitive interactions among multiple non-native salmonids and two populations of Atlantic salmon. Ecology of Freshwater Fish 24: 44-55. |PDF|


Stanfield LW, Gibson SF, Borwick JA. 2006. Using a landscape approach to identify the distribution and density patterns of salmonids in Lake Ontario tributaries. Am Fish Soc Symp 48, pp. 601-621. Available at:

Van Zwol JA. 2011. Interspecific competition among juvenile salmonids: Social behaviour and hormone levels of Atlantic salmon and two non-native trout species. Master of Science thesis, University of Western Ontario, London, Ontario.



Research Projects

Pacific salmon
gene expression

Lake Ontario
Atlantic salmon



Last updated January 2018
© Aimee Lee Houde