Burbot

Appearance

With an appearance like a cross between a catfish and an eel, the burbot has a serpent-like body, but it is easily distinguished by a single barbel on the chin. The body is elongated and laterally compressed, with a flattened head and single tube-like projection for each nostril. The mouth is wide, with both upper and lower jaws consisting of many small teeth. Burbot have two soft dorsal fins; he first being low and short, the second being much longer. The anal fin is low and almost as long as the dorsal fin. The caudal fin is rounded, the pectoral fins are fan-shaped, and pelvic fins are narrow with an elongated second fin ray. Having such small fins relative to body size indicates a benthic lifestyle with low swimming endurance, unable to withstand strong currents. The circular or cycloid scales are very small, making it difficult to accurately age, and thus even more challenging to manage.

Naming

The name burbot comes from the Latin word ''barba'', meaning beard, referring to its single chin whisker, or barbel. The genus and species name "lota" comes from the old French ''lotte'' fish named also "barbot" in this language. The Inuktitut–Iñupiaq word for burbot was also used to name the recently discovered extinct transitional species ''Tiktaalik''.

Distribution

Burbot have circumpolar distribution above 40°N. Populations are continuous from the British Isles eastward across Europe and Asia to the Bering Strait. On the North American side, burbot range eastward from the Seward Peninsula in Alaska to New Brunswick along the Atlantic coast. Burbot are most common in streams and lakes of North America and Europe. They are fairly common in Lake Erie, but are also found in the other Great Lakes. Recent genetic analysis suggests the geographic pattern of burbot may indicate multiple species or subspecies, making this single taxon somewhat misleading.

Status

Burbot populations are difficult to study, due to their deep habitats and reproduction under ice. Although burbot global distribution is widespread and abundant, many populations have been threatened or extirpated. Lacking popularity in commercial fishing, many regions do not even consider management plans. Pollution and habitat change, such as river damming, appear to be the primary causes for riverine burbot population declines, while pollution and the adverse effects of invasive species have the greatest influence on lacustrine populations. Management of burbot is on low priority, being nonexistent in some regions.

Habitat

Burbot live in large, cold rivers, lakes, and reservoirs, primarily preferring freshwater habitats, but able to thrive in brackish environments for spawning. During the summer, they are typically found in the colder water below the thermocline. In Lake Superior, burbot can live at depths below 300 m . As benthic fish, they tolerate an array of substrate types, including mud, sand, rubble, boulder, silt, and gravel, for feeding. Adults construct extensive burrows in the substrate for shelter during the day. Burbot are active crepuscular hunters. Burbot populations are adfluvial during the winter months, and they migrate to near-shore reefs and shoals to spawn, preferring spawning grounds of sand or gravel.

Food

At the larval stage, month-old burbot begin exogenous feeding, consuming food through the mouth and digesting in the intestines. Burbot at the larval stage and into the juvenile stage feed on invertebrates based on size. Under 1 cm, burbot eat copepods and cladocerans, and above 1 and 2 cm, zooplankton and amphipods. As adults, they are primarily piscivores, preying on lamprey, whitefish, grayling, young northern pike, suckers, stickleback, trout, and perch. At times, burbot will also eat insects and other macroinvertebrates, and have been known to eat frogs, snakes, and birds. Having such a wide diet is also correlated to their tendency to bite lures, making them very easy to catch. Burbot are preyed upon by northern pike, muskellunge, and some lamprey species.

Predators

At the larval stage, month-old burbot begin exogenous feeding, consuming food through the mouth and digesting in the intestines. Burbot at the larval stage and into the juvenile stage feed on invertebrates based on size. Under 1 cm, burbot eat copepods and cladocerans, and above 1 and 2 cm, zooplankton and amphipods. As adults, they are primarily piscivores, preying on lamprey, whitefish, grayling, young northern pike, suckers, stickleback, trout, and perch. At times, burbot will also eat insects and other macroinvertebrates, and have been known to eat frogs, snakes, and birds. Having such a wide diet is also correlated to their tendency to bite lures, making them very easy to catch. Burbot are preyed upon by northern pike, muskellunge, and some lamprey species.

Evolution

Burbot reach sexual maturity between four and seven years of age. Spawning season typically occurs between December and March, often under ice at extremely low temperatures ranging between 1 and 4°C. Though a relatively short season lasting from two to three weeks, burbot will spawn multiple times, but not every year.

As broadcast spawners, burbot do not have an explicit nesting site, but rather release eggs and sperm into the water column to drift and settle. When spawning, many male burbot will gather around one or two females, forming a spawning ball. Writhing in the open water, males and females will simultaneous release sperm and eggs. Depending on water temperatures, the incubation period of the eggs lasts from 30 to 128 days. Fertilized eggs will then drift until they settle into cracks and voids in the substrate.

Depending on body size, female burbot fecundity ranges from 63,000 to 3,478,000 eggs for each batch. Rate of growth, longevity, and age of sexual maturity of burbot are strongly correlated of with water temperature: large, older individuals produce more eggs than small, younger individuals. Eggs are round with a large oil globule, approximately 1 mm in diameter and have an optimal incubation range between 1 and 7°C .

Newly hatched burbot larvae are pelagic, passively drifting in the open water. Habitats about 12°C are known to be intolerable for larval burbot. By night, juveniles are active, taking shelter during the day under rocks and other debris. Growing rapidly in their first year, burbot reach between 11 and 12 cm in total length by late fall. During the second year of life, burbot on average will grow another 10 centimetres .

Burbot transition from pelagic habitats to benthic environments as they reach adulthood, around five years old. Average length of burbot by maturity is about 40 cm , with slight sexual dimorphism. Maximum length ranges between 30 and 120 cm , and weight ranges from 1 to 12 kg .