New AFS report details threats to Western trout

 

The American Fisheries Society just released a peer-reviewed report on the diversity and conservation status of trout in western North America from coastal rainbows in Alaska to undescribed trout in Mexican highlands. More than 20 species and subspecies of trout are covered, including a relatively unknown complex of trout species from the Sierra Madre Occidental of Mexico that appear to have originated from migratory steelhead or perhaps by ancient headwater flow exchanges from the southernmost reaches of the Rio Grande drainage.

 

Dr. Brooke Penaluna of the U.S. Forest Service at Oregon State University led a group of 22 top salmonid scientists from across the continent in preparing the report.  

 

As the report describes, the evolutionary history of trout is fascinating but complicated owing to the great morphological, behavioral  and life history variation found within each species. As a group, trout have been quite successful. Trout of the genera Oncorhynchus (e.g., cutthroat trout) and Salmo (e.g., brown trout) are believed to have shared a common ancestor 15-35 million years ago.  

 

The report is featured in the June 2016 issue of Fisheries Magazine, published by the American Fisheries Society.

 

Yet despite these old and diverse evolutionary lineages and current broad distributions, many trout species are under threat. The report includes a timeline of threats ranging from the legacy of historical disturbance associated with practices such as mining, logging and livestock grazing, to more recent problems caused by invasive species, climate change and, in remote areas, even the illicit drug trade.  Across the continent, human population growth continues to exert pressures through land conversion, urban expansion and increasing water demands.

 

 

 

The current distributions of native trout are fragmented and isolated compared to historical conditions. Fish have been moved above falls and artificial barriers to isolate them from downstream non-native fishes but this isolation renders populations increasingly vulnerable to drought, wildfires and other extremes of our changing climate. Many strategies are suggested to deal with the threats but the authors primarily encourage education-based collaborations across watersheds that link private lands with public lands and restore larger, interconnected stream networks for trout habitat while employing strong monitoring programs and adaptive management. 

 

Even for us scientists, the beauty and diversity of trout impress beyond words. Amazingly in this day and age, some species of trout remain virtually unknown and unnamed. I think that is a good thing. Whether scientist or angler, discovering the beauty of a new trout is well worth the journey. This report provides some enticing hints about what is out there beyond our more familiar streams.