Why do Biologists love introducing species to try and fix a problem? Are we ever going to learn our lesson? Look at the Cane Toad in Africa, the Mongoose in the Caribbean, and the Nile Perch, all of these were introduced by people into a new ecosystem and every one of them decimated the native species. So why are Biologists trying to get non-native species to become established in a Colorado Lake? Apparently, it is their proposed solution to reducing the over abundant population of Opossum Shrimp (Mysis diluviana) that was introduced in the 1970’s. So can two wrongs make a right?

 

The Problem

Mysis1
Above- an Opossum Shrimp. Photo credit Peter Bryant 2013

The Opossum Shrimp was originally introduced into Lake Dillon as a means to increase the size and population of the fish in lake. What was not taken into account was the differences in diel vertical migrations (DVM), which is the daily migratory patterns that aquatic species take (The American Naturalist).The trout and salmon in the lake were on diurnal migratory patterns, where they would rise to the surface during the day and feed on plankton and other food sources then, as night approached, they would go deeper into the lake. The Opossum Shrimp had the opposite migratory patterns, being nocturnal, they would spend the days deep in the lake, and as night came on they would migrate to the top and feed. Thus, the two populations had very little to no interaction.

“Mysis can virtually eliminate large zooplankton that support growth of trout and salmon in reservoirs”-Devin Olsen

But how much damage could a little shrimp do? They are tiny, right? Well, being small has its advantages.Sticky 1  As is common in Biology, when a species is introduced into an ecosystem without any predators, its population quickly booms and surpasses the carrying capacity of the ecosystem followed by a crash of the ecosystem; in other words, the shrimp’s population increased so rapidly that it reached a point where there was not enough food to support the ecosystem. This was a real problem for the fish in the lake, which became small in size and numbers. Typically when we talk about an introduced species wreaking havoc on an ecosystem it is because they are a predator and its prey, the native species, are naïve  (in the sense that they do not know to fear the predator). In this case we almost see a naïve predator being undone by an introduced prey.

arcticchar

Above- An Arctic Char, caught by Devin Olsen. Devin Olsen is a Master’s student at CSU who studied the Arctic Char population and other aspects of the Lake Dillon fishery. Photo Credit Devin Olsen (via Denver Post)

Why the Arctic Char?

Sport fishing is a year-round event in these mountain towns bringing in a lot of revenue, both for the locals and the state. Thus, having a beautiful lake just off of I-70 void of game fish is a real detriment. So why introduce the Arctic Char? Well, there are several reasons Sticky 2that make it the ideal candidate. Primarily, it is a known predator of the Opossum shrimp in their native home range, making it perfect for reducing the shrimp population, in theory.

Besides it being a natural predator for the shrimp, it has the potential to shift Lake Dillon from a desolate nightmare to a fisherman’s and ecologist’s dream. By introducing the Char, they brought in a species of fish that is a rarity in the lower 48 states, only occurring
in a few other continental states (Maine and New Hampshire)(FishBase). Colorado is one of two western states that currently has the Char (see the distribution map below). Aside from being a rare species (locally), it is also an incredible sport fish, it’s vibrant breeding colors and hard fighting when hooked make it a fun fish to reel in.

Distribution

Above- Distribution of the Arctic Char in the USA. Tan area (Alaska) is the natural homerange. The larger spots imply larger populations. Photo credit USGS mapping.

Moving Forward

Sadly, since the introduction of the Arctic Char in 1990 there has only been a small impact on the shrimp population (CSU). This is to be expected though, as the shrimp population had a 20 year head start and is very well established. It has not been until recently that the Char was noted to be sustaining its population naturally, versus yearly stocking; which is a good sign for the Char and a very good sign for the Lake’s health as a whole.

If the Char can become well established in the lake, Lake Dillon will be the only public fishery in the lower 48 states where the Arctic Char can be caught, quickly making it a destination for sport fishers. It has been estimated that if Lake Dillon is successful in becoming a “Boutique Fishery” (a fishery specializing in a certain species), it can potentially bring in $1.3 billion annually for Colorado (Denver Post). This coupled with the potential of bringing the lake back into a healthy equilibrium makes the introduction and continual studying of the Arctic Char and Lake Dillon as a whole extremely important. By continuing to establish the fishery we are supporting a community of people and saving an aquatic community before it completely crashes.

 

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