Invasive Trout Introduce Problems
Movement of Fish for Sport Affects Frogs and Native Trout Species
As awareness of trouble caused by introduced species increases, efforts are being made to undo damage done by intentional trout release for sport fishing worldwide.
The ecological damage caused by many years of moving fish species from one habitat to another is just now beginning to be redressed. Trout have been one of the most commonly translocated fish with introduced species found in North and South America, Australia, Africa and Asia. Now attempts are being made to restore local native species, reverse habitat degradtion and remove the invasive alien trout.
Introduced Trout Found Worldwide
Fishing is a popular sport. Trout fishing in lakes, ponds and streams spread throughout the world, along with western civilization. Sport fishermen travel from place to place, judging the local fish by how difficult they are to catch. And they have traditionally brought back species that are especially challenging to be introduced into their local waterways.
For example, brown trout (Salmo trutta) was introduced into US waters from the UK in the 1880s. It has also been introduced in South America, Asia, Africa and Australia. The brook trout (Salvelinus fontinalis), an eastern US species, has been spread throughout the country, causing problems in the mountain and far west states.
Danger to Amphibians
Australia is also struggling with introduced rainbow trout (Onchorhynchus mykiss). The two non-native trout species are decimating the populations of critically endangered spotted tree frogs (Litoria spenceri). In the US, the yellow legged mountain frog (Rana muscosa) is disappearing as rainbow, golden (Oncorhynchus mykiss aguabonita) and brown trout all prey on it. Both species of frog are also threatened by chytrid fungal disease and habitat degradation. For the yellow legged frogs, much of their habitat was small lakes in the Sierra Nevada where no fish existed prior to introductions of trout for sport fishing. These frogs have no way to protect themselves from a brand new predator.
Danger to Local Native Trout
The introduced alien trout in each place are doing better than native species. Most of the thirteen species of cutthroat trout (Oncorhynchus clarki) native to the Pacific coast of North America have been pushed out by brown, brook and rainbow trout. And, in ironic twist of fate, the brown trout in the UK is struggling to maintain a foothold against brook trout introduced from the US.
Restoring Native Species and Biodiversity
In some areas, habitat restoration is helping the native trout recover The US National Fish Habitat Action Plan, approved in 2006, is being implemented using coalitions of local state and federal agencies and interested parties. The idea is to focus on restoration of waters that the local native trout prefer. Steps include transforming old drainage ditches into meandering streams with overhanging trees, gravel and stone bottoms and fencing to important stretches to prevent cattle from damaging the riverbanks.
No limit fishing of the edible alien trout and electrofishing are being used to try to reduce populations of non-native trout species.
In some cases, poisons such as rotenone and antimycin, are being used to kill the introduced species. There is concern about the use of poisons given that restoration of biodiversity, not just individual trout species, is the underlying aim. It remains to be seen whether these measures will backfire as human meddling so often does. This process will be one to watch very closely.
