Golden Mussles in ONeill Forebay

My last fishing day in October was, as usual, very satisfying. October and November are prime months in the forebay, with large schools of shad moving through, drawing in aggressive stripers eager to chase flies. Today’s action was consistent—I found fish nearly everywhere I looked. Most were smaller, around 15-17 inches, but I did manage to hook about half a dozen larger ones in the 18-22 inch range by slowly working flies along the bottom. Using the livescope, I could spot and target them with precision. I wrapped up the day with 35 fish, though most were on the smaller side. There were a few brief blitzes, but nothing sustained. All in all, it was a solid day on the water.  I lost a nice one today at the boat and it seemed like the fish were at times lazy possibly full from  feeding on the abundant shad this last month.

I rolled into O’Neill Forebay this morning and was informed that due to the discovery of Chinese Golden Mussels,  boats will have to be inspected going out before rebanding.   This will include all kayaks and float tubes as well.   I think they are more worried about spreading the Golden Mussels to other watersheds vs keeping them out of the forebay.   It seems the Golden Mussels were recently introduced into the forebay via the aqueduct.  As of today,  here are the new rules:

An invasive Mussel Species new to the U.S.  believed to be the Golden Mussel has been discovered in waters of the San Luis Reservoir State Recreation area.   To help prevent the spread of these mussels to other areas of the state and elsewhere, the following procedure will be implemented.  Upon exiting , all trailered vessel with motors and kayaks with motors including vessels transported in pickup trucks (float tubes)  will be inspected.  Park staff will confirm that the bilge plugs have been removed,  bilge drained, and outboard motors an outdrives have been lowered.,   Liv Wills must be drained,   Park staff will also check for attached aquatic plants on vessels and trailers.   The state park green seal will then be attached to trailered vessels.  Remember to raise your motor or outdrive after inspection to prevent damage.   Always remember:  CLEAN, DRAIN AND DRY.   Thank you for your cooperation and for visiting San Luis Reservoir State Recreation area.

Golden mussels (Limnoperna fortunei) are native to freshwater and estuarine environments in China and Southeast Asia. They originally thrived in rivers and lakes in these regions. The species was inadvertently introduced to other parts of the world, primarily through ballast water discharge from ships. This process likely carried the mussels to South America, where they were first detected in Argentina in the early 1990s, and have since spread to other parts of the continent, including Brazil and Paraguay.

Today, golden mussels are considered invasive in South America, where they have significantly impacted local ecosystems. There’s concern they may spread to North America and other continents, potentially causing similar ecological and economic problems.

Eradicating golden mussels is extremely challenging, particularly once they’re established in an ecosystem. Their rapid reproduction rate and ability to survive in various water conditions make them tough to eliminate. Here are some methods attempted in various regions:

  1. Chemical Treatments: Chemicals like potassium chloride or chlorine have been used in enclosed systems to kill golden mussels. However, these are not ideal for open water bodies, as they can harm native species and disrupt the ecosystem.
  2. Physical Removal: In small areas, physical removal (scraping and suction) is possible but labor-intensive and often ineffective at a large scale due to the mussels’ high reproductive rate.
  3. Environmental Management: Controlling water temperature or salinity can sometimes curb mussel growth, but this approach isn’t feasible in most natural bodies of water due to the potential impacts on other organisms.
  4. Biological Control: Researchers have looked into biological control, like introducing natural predators or pathogens specific to golden mussels. However, this is still largely experimental and carries risks of unintended consequences.

The best current strategy remains prevention—monitoring and controlling the movement of watercraft and equipment between bodies of water to avoid spreading them.

As for the fishing in the forebay.  The long term impact of  Golden mussels  could be substantial due to the ways they alter the ecosystem. Here’s what might happen:

  1. Changes to Food Web: Golden mussels are filter feeders, consuming large quantities of plankton. By depleting this food source, they can disrupt the food chain specifically the Threadfin Shad and Delta Smelt populations,  reducing food availability for these forage fish that rely on plankton.
  2. Habitat Alteration: Golden mussels attach to almost any hard surface, forming dense colonies on rocks, docks, and even other aquatic organisms. This can crowd out native mussel species and disrupt habitats where fish spawn or hide, possibly reducing fish populations.
  3. Water Quality and Clarity: Because they filter plankton, golden mussels increase water clarity. While this might sound positive, it often leads to more sunlight penetration, which can fuel algae growth, particularly of harmful algae species that can produce toxins. This effect could reduce water quality and make the lake less suitable for fish and other wildlife.
  4. Indirect Effects on Fish Health: Changes in water clarity and algal growth could also alter oxygen levels, leading to conditions that stress certain fish species. Predatory fish might also be impacted if their prey populations decline due to altered food availability.
  5. Fishing Infrastructure and Equipment: Golden mussels can attach to boats, pipes, and fishing equipment, creating maintenance issues and increasing costs for fishery management. They can also clog water intake systems, which impacts local water management and habitat conditions.

The effect of these invasive mussel species to the Forebay and Lake will be different since the water in the forebay is replenished more rapidly.  In lakes, quagga and golden mussels can cause significant water clarity by filtering out plankton, which affects the entire food web. This water clarity might initially seem beneficial for predatory fish like striped bass, which rely on visibility for hunting.  However, the loss of plankton depletes the base of the food chain, leading to fewer forage fish over time. In lakes, this effect is more pronounced and stable because there isn’t a flow of new nutrients.  Mussels can also colonize lake substrates more densely, covering rocks, sand, and submerged structures. This often changes the habitat for other species, sometimes favoring certain fish or plant species but often leading to a net loss of biodiversity..

In moving water like the O’Neill Forebay, the  mussels may have a different impact due to the constant movement of water and nutrients. Nutrients and plankton are frequently replenished by the aqueducts, which can buffer some of the depletion effects seen in lakes.  Mussels can still filter water and reduce plankton locally, but moving water systems may slow down this depletion compared to a closed system like a lake. This can create pockets of clear water, potentially benefiting visual predators like striped bass in those areas, but not as uniformly as in lakes.  The invasive mussels can alter the structure of the riverbed, but because rivers are more dynamic, they don’t create the same extensive carpet as they do in lakes. The mussels’ attachment points can still restrict habitat for other species, but it’s often more dispersed due to the flow of the water.

Only time will tell what impact this will have on us as fly fishermen. I’ve been fishing this lake and forebay for as long as I can remember, and there have always been mussels and clams here, so maybe it’s not as new a phenomenon as the biologists suggest. Some of my friends, especially those who lean towards believing in climate change, think global warming is what’s behind the decline in fishing here. Really?  At least that’s how they vote.   My takeaway is to live for today, because these are the good old days. Besides, I probably only have about 15 more years to fish this lake before I’m too old. More water has flowed under my boat and float tube than what’s left ahead and fishing has recently been great.

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