May 4, 2009

Trout Impacts and Stocking Controversies - Beyond California

Much of the recent research on impacts of trout stocking has focused on aquatic ecosystems in California. However, a research program in Maine is now showing just how pervasive these impacts are. Most of Maine's naturally fishless lakes (and there were thousands of them historically) have now been stocked with numerous fish species, including brook trout, and all indications are that these introductions have had similar effects as those documented in California's Sierra Nevada and elsewhere - the disappearance of amphibians and conspicuous invertebrate taxa. The New York Times ran a story last week that provides an interesting overview of what the Maine research is turning up.

On the opposite coast, the practice of trout stocking continues to cause controversy in North Cascades National Park. This is the only national park in the country in which fish stocking is still allowed, but after many years of debate about the practice and detailed scientific study it appears that trout stocking may be on its way out. A recent Associated Press story provides the details.

Back to The Mountain Yellow-legged Frog Site.


  1. The vital information that the statement above leaves out is that the 12 year scientific based study found in the EIS on fish stocking for the North Cascades National Park concludes that there is NO harm done to the amphibians or any other species as long as the stocking of fish is done in low densities (approx 20 fish per acre per year) with non-reproducing fish.

    It is possible that this circumstance only applies to the species found in the Northwest (e.g., long toed salamander), but I doubt it. Folks who study these things tend to lump lakes with excessive populations of fish with all other lakes. Once this distinction is made, it is clear that with proper management stocked fish can usually co-exist very nicely with all other species in a lake.

    Sandy McKean

  2. Hi Sandy. Thanks for the post. I didn't mention the specifics related to trout stocking densities because these details were provided in the New York Times article that I pointed readers to. Numerous studies have shown that trout density is an important determinant of the severity of trout impacts to the native community. This includes one of my studies conducted on trout impacts in Yosemite National Park (Knapp, R. A., C. P. Hawkins, J. Ladau, and J. G. McClory. 2005. Fauna of Yosemite National Park lakes has low resistance but high resilience to fish introductions. Ecological Applications 15:835-847 - available here:

  3. Roland, I'm confused by your reply. I've read the NY Times article carefully, and I can find no reference to stocking densities in that article. The article only talks about fishless lakes (i.e., no stocking occurs) and lakes with fish. The article clearly implies that fish in the lakes studied have harmed other species, whereas fishless lakes are healthy. Did I miss a section in the article that discusses fish stocking resulting in low density fish populations has little if any impact on the biota of the lake? If so, I sure can't find ANY mention of "the specifics related to trout stocking densities".


  4. My apologies - I meant the AP story published in the Seattle Times that I also provided a link to in the original blog post. This article makes specific reference to the different impacts of trout stocked at high versus low densities. Sorry for the confusion.