The question of whether the burbot (Lota lota) is an invasive species lacks a simple answer. This unique freshwater fish, the only freshwater member of the cod family (Gadidae), is a natural part of many northern ecosystems. However, when transported outside of its vast native range by human activity, it can become a highly problematic non-native predator. The burbot’s designation depends entirely on its geographic location, existing as either a native species in northern latitudes or an ecologically disruptive invader in southern river basins.
Defining the Burbot and Native Distribution
The burbot is instantly recognizable by its elongated, eel-like body and the single barbel on its chin, which gives rise to its name, derived from the Latin word barba, meaning beard. This demersal species prefers the deep, cold waters of large lakes, reservoirs, and rivers, typically remaining below the thermocline during the warmer months. They are the sole representatives of the cod order (Gadiformes) in freshwater habitats, a lineage that includes marine species like the common cod and haddock.
Its native distribution is one of the most extensive of any freshwater fish, covering a circumpolar range across the Northern Hemisphere above approximately 40° N latitude. This includes vast territories in North America (Alaska to the Atlantic coast) and across Eurasia (northern Europe and Russia). Within these native systems, the burbot functions as a natural apex predator, feeding on aquatic invertebrates when young and primarily on fish as adults.
The burbot is significant in these northern regions, not just ecologically, but also as a popular sport fish harvested during ice fishing season. It is a cold-water specialist, requiring frigid temperatures, often under the ice, to spawn during the winter months. This reproductive requirement naturally limits its ability to colonize warmer southern waters without human intervention.
Assessing Invasive Status in Non-Native Waters
The burbot is classified as an invasive species when introduced into river systems where it did not historically exist, often resulting from unauthorized or illegal stocking. Introducing the species outside of its natural boundaries creates an ecological imbalance, as native fish populations have not evolved defenses against this new, efficient predator. This occurred in the Green River Drainage, a major tributary of the upper Colorado River Basin in the Western United States.
Burbot were illegally introduced into the Green River system, likely starting in Big Sandy Reservoir in Wyoming in the mid-1990s. The population rapidly expanded from this initial point, colonizing reservoirs like Fontenelle and Flaming Gorge, and spreading downstream. The success of this non-native population is due to the reservoir habitats, which mimic the deep, cold-water conditions of their native range, allowing them to thrive quickly.
State and federal management agencies consider the burbot a major threat in this basin, leading to specific regulatory actions. In Utah and Wyoming, resource managers have implemented a “no tolerance” fishing regulation, strictly mandating that any burbot caught by an angler must be killed immediately and cannot be released back into the water. This aggressive management response highlights the regulatory distinction between the burbot’s native status in northern states and its invasive designation in the Colorado River system.
Ecological Consequences of Non-Native Burbot
The non-native burbot populations exert considerable pressure on the receiving ecosystems through their behavior as nocturnal, opportunistic predators. As adults, burbot are efficient piscivores, meaning their diet consists almost exclusively of other fish. This predatory habit has resulted in direct and severe impacts on ecologically and economically important fish species in the Green River Drainage.
A primary concern is their predation on endangered native species, such as the flannelmouth and bluehead suckers, which are already struggling due to habitat alteration from dams. Burbot consume these smaller native fish, further hindering conservation efforts aimed at restoring native fish populations. They also negatively affect recreational fisheries by preying heavily on sport fish, notably causing a documented decline in kokanee salmon populations within Flaming Gorge Reservoir.
Their life history traits, including high fecundity and the ability to mature relatively early in the Green River system, contribute to their rapid population growth and persistence. The difficulty in controlling established burbot populations is compounded by their preference for deep water and rocky substrates, which makes traditional removal methods less effective. Consequently, management efforts often involve intensive suppression programs, including incentivized fishing derbies and targeted chemical treatments, to limit the devastating ecological consequences of this non-native predator.