Challenges in recovering imperilled fishes

There have been many studies that point to the imperilment of freshwater fishes around the world. Over the last century, freshwater fishes have seen the highest rates of extinction among all North American vertebrates1, with 57 species of freshwater fish recognised as Special Concern, Threatened, or Endangered in Canada. In the Great Lakes Basin, the number of fish species has declined over the last 200 years from 169 species to 148 species2. Conservation actions are therefore needed to reverse these trends and recover imperilled fish species.

Recovering imperilled species is a complex undertaking and strategies will vary depending on the species, location, habitat, and costs. One approach for recovering imperilled species is species repatriation (also known as species reintroduction). Species repatriation describes the act of intentionally releasing individuals back to their native range in areas where that species was recently extirpated. Although the definition of repatriation may be clear, the act of repatriation is complicated and rarely done.

Naturalized male Rainbow trout (Oncorhynchus mykiss) caught in an Ontario stream

You may be thinking to yourself, complicated … have we not introduced fish into the wild for decades? Yes, we have. Sport fish have been released across North America for well over a century to enhance recreational angling. In some cases, sport fish introductions have occurred within the species’ native range to offset the impacts of angling mortality. In other cases, sport fish have been introduced outside of their native range to develop or enhance a recreational fishery. A well-known example is Rainbow Trout (Oncorhynchus mykiss). Rainbow Trout are native to the North American Pacific coast, but have been successfully introduced to lakes and streams of almost all North American states, provinces, and territories3. Albeit successful in establishing recreational fisheries, Rainbow Trout introductions have come at a cost to native species – for example, hybridisation with introduced Rainbow Trout threatens the integrity of the native Westslope Cutthroat Trout4, a species currently recognised as Special Concern under the Species at Risk Act in Canada.

Eastern Sand Darter (Ammocrypta pellucida) Photo Credit: Alan Dextrase – OMNRF

However, imperilled fish species tend to get less attention than sport fishes. In fact, I would argue that most of society would not recognise an imperilled fish species if they were to see one in the wild. Given the rarity factor of imperilment and the fact that most imperilled freshwater fishes are small in size5, observations of these species in the wild is challenging. For instance, the Eastern Sand Darter (Ammocrypta pellucida) is a species listed as Threatened under the Species at Risk Act in Canada that few people can say they have seen. The average adult in Ontario is 6 cm in length and their yellow-translucent colour, burrowing behaviour, and limited geographic range6 makes this species truly difficult to find.

Eastern Sand Darter (Ammocrypta pellucida) burrowing Photo Credit: Alan Dextrase – OMNRF

The bias towards sport fishes also resonates in the scientific literature, as much less is known about the ecology of imperilled fishes, creating a barrier for potential repatriation efforts. For example, information on the spawning habitat requirements of imperilled species can be critical for successful introductions, but is often unknown. Furthermore, repatriation is likely to fail if the initial cause of extirpation has not been addressed. If an invasive species caused a local extirpation due to their predatory or competitive behaviour, releasing individuals of the imperilled species may be just simply feeding the problem (literally) and a wasted effort.

There are several other challenges for repatriation that include where to obtain the individuals for repatriation, when and at what age should introductions occur, among others. Despite the challenges, it is likely that repatriation of fishes will continue to gain steam across North America as more fish species are lost across their historical ranges.

As anglers, what can we do? The most important tool we have is knowledge – learn about the imperilled species in your area and be cognisant of your actions within their habitat. Repatriation efforts can only succeed when threats to species are removed and habitat is restored.

Karl A. Lamothe


  1. Burkhead, N.M. 2012. Extinction rates in North American freshwater fishes, 1900–2010. BioScience 62: 798–808.
  2.  Mandrak, N.E., and Cudmore, B. 2010. The fall of native fishes and the rise of non-native fishes in the Great Lakes Basin. Aquatic Ecosystem Health and Management 13: 255–268.
  3. Crawford, S.S., and Muir, A.M. 2008. Global introductions of salmon and trout in the genus Oncorhynchus: 1870–2007. Reviews in Fish Biology and Fisheries 18: 313–344.
  4. Olden, J.D., Hogan, Z.S., and Vander Zanden, M.J. 2007. Small fish, big fish, red fish, blue fish: size-biased extinction risk of the world’s freshwater and marine fishes. Global Ecology and Biogeography 16: 694–701.
  5.  Hitt, N.P., Frissell, C.A., Muhlfeld, C.C., and Allendorf, F.W. 2003. Spread of hybridization between native westslope cutthroat trout, Oncorhynchus clarki lewisi, and nonnative rainbow trout, Oncorhynchus mykiss. Canadian Journal of Fisheries and Aquatic Sciences 60: 1440–1451.
  6. Holm, E., Mandrak, N.E., and Burridge, M.E. 2009. The ROM Field Guide to Freshwater Fishes of Ontario. ROM Science Publication. Friesens Printers, Altona, Manitoba.


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