Faraway Fly Fishing

Even five months after the eruption of the Puyehue Volcano in the Cordón Caulle Mountains in southern Chile, volcanic ash continues to fall on Bariloche. New information and conclusions about the effects of this ash continually emerge, creating confusion and pure conjecture over what the real environmental impact will be in the short, medium and long-run. The future of our area’s trout population is a source of serious concern for us, so we set out to gather the best scientific and anecdotal evidence currently available to try and answer this pressing question.  Born and raised in Bariloche and having lived through the worst of the eruption, this issue hits very close to home – literally.

Since the eruption of Puyehue on June 4th, various locations and watersheds have been affected, the severity of which has depended entirely on wind direction.  As of now, one of the most seriously impacted areas is Villa la Angostura, 38 km southeast of Ground Zero, and directly in line with the prevailing winds. On the opposite side of Lago Nahuel Huapi in Bariloche, ash continues to fall intermittently, but generally in lower proportions. Almost every day we can see the plume of the volcano pass just in front of our city over the opposite coastline.

Due to its proximity to the volcano and immense surface area, Lago Nahuel Huapi has received the lion’s share of volcanic ash. The most affected parts of the lake are the Última Esperanza, Rincón, Machete and Huemul arms.  Relatively unaffected are the Blest, Tristeza and Companario arms, thanks to their more protected locations. In addition to Lago Nahuel Huapi, lakes Totoral, Espejo, Correntoso and Traful have all been seriously affected as well. Thankfully, lakes Gutierrez, Mascardi, Los Moscos, Hess and Roca have received almost no ash at all. Many of the streams close to the volcano have also been blanketed with ash, but owing to the heavy spring run-off, much of the sediment has already been flushed out.

So what will the ultimate impact on our aquatic organisms be? It’s difficult to say, but biologists and anglers alike have witnessed normal spawning activity from trout, percas, and other fish, suggesting that the environmental changes haven’t negatively impacted reproduction. Even in the Limay and Correntoso, which during the worst of the eruption ran color of cement, fishermen are witnessing strong spawning activity. Official surveys conducted by local parks and wildlife agencies have also captured specimens of rainbow, brown and brook trout in optimal conditions, even in the most severely affected areas such as Villa la Angostura. All signs suggest that the catastrophic eruption hasn’t been noticeably detrimental to adult trout or their primary food sources. The real question, however, is how the baseline ecological changes (e.g. oxygen & PH levels), will impact the organisms at the bottom of the food chain, and thus the long term productivity of the ecosystem.

According to a scientific study that haven’t been finalized yet, the aquatic organism most at risk to drastic change is the zooplankton, as it forms the base of the aquatic food chain. Most species of fish and various invertebrates depend on zooplankton as an important food source. In addition to zooplankton, we can include cladocera, copepoda, and amphipods – tiny crustaceans that constantly filter the water in search of phytoplankton. During this process they constantly ingest ash particles (comprised largely of silica), and it appears that this can lead to death by lesions to the filtration and digestive systems.  If this proves to be true on a massive scale, then the long-run impact on our trout could be severe indeed. At the moment, however, this doesn’t seem to be the case, as indicated by the healthy condition of our fish.

Let’s also not forget that with time, volcanic ash can have a very beneficial influence on the ecosystem, acting as a fertilizer and improving its overall productivity. Numerous cases throughout history have shown this to be a very real possibility, so in the future perhaps our fishing will be better than we could have ever imagined.  At least the situation doesn’t appear to be nearly as dire as one might imagine by looking out the window at the occasional plum of ash, but let’s keep our fingers crossed anyhow!

Thanks to Hugo Dezurko and Ruben Martin for the pictures from the scouting in Villa la Angostura area.

Tags: nahuel huapi, Volcan Puyehue