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Arizona River threatened by invasion of a voracious predator

Scott Ferguson

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I did my MS in Arizona... the rivers and streams there have an amazing assortment of local and weird specialties, which is what happens in isolated habitats. They are the aquatic equivalent of the Hawaiian Islands.


I saw stream communities that were totally devastated by green sunfish and crayfish, both of them introduced since the 1950s. Invasive bullfrogs are doing huge damage to wetlands, eating everything they can cram in their big mouths. Smallmouth bass are already notorious for their effects on California streams, as are rainbow trout for their effects on lakes.


With time some of the natives will likely adapt or the exotics will be regulated by diseases that catch up with them in their new digs. But a lot of the native species are just terribly vulnerable to predators. I studied a desert damsefly that had a neat adaptation to dropping water levels in the early fall: the adults would crawl way down deep to lay their eggs, carrying a film of air on their bodies like SCUBA divers. Not compatible with fish.


What do anglers care? Sometimes exotic species support an incredible fishery. Other times, they reach huge densities that are food-limited and you wind up with a habitat full of scrawny fish that nobody wants to catch anyway. In my book the species native to isolated habitats have an intrinsic right to exist, and I think most anglers would rather fish for native species interacting with others in a rich community... or if a stream is naturally fishless, just take a hike with the camera and see how it bursts with life.

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