Burbot: Ecology, Management, and Culture

Abstract.—Burbot <em>Lota lota </em>populations collapsed in four of the five Laurentian Great Lakes between 1930 and the early 1960s. Collapses in Lakes Michigan, Huron, and Ontario were associated with sea lamprey <em>Petromyzon marinus </em>predation, whereas the collapse in Lake Erie was likely due to a combination of overexploitation, decreased water quality, and habitat degradation. We examined time series for burbot population density in all five lakes extending as far back as the early 1970s to present time and characterized the long-term trends after the initial collapses. Burbot population density in Lake Superior has remained relatively low and stable since 1978. Recovery of the burbot populations occurred in Lakes Michigan and Huron during the 1980s and in Lake Erie during the 1990s. Control of sea lampreys was a requirement for recovery of burbot populations in these three lakes. Declines in alewife <em>Alosa pseudoharengus </em>abundance appeared to be a second requirement for burbot recovery in Lakes Michigan and Huron. Alewives have been implicated in the decline of certain Great Lakes fish stocks that have pelagic larvae (e.g., burbot) by consuming the pelagic fry and possibly by outcompeting the fry for food. Relatively high populations of adult lake trout <em>Salvelinus namaycush </em>compared to burbot served as a buffer against predation by sea lampreys in Lakes Huron and Erie, which facilitated recovery of the burbot populations there. Although sea lampreys have been controlled in Lake Ontario, alewives are probably still too abundant to permit burbot recovery.

Burbot: Ecology, Management, and Culture

Abstract.—Adult burbot <em>Lota lota </em>from Koocanusa Reservoir, Montana, USA were surgically implanted with acoustic (<em>n </em>= 28) and combined radio/acoustic tags (<em>n </em>= 12) to quantify movements and home range. Fish were tagged from November 2003 to April 2004, and tracking efforts were conducted approximately weekly during daylight hours on Koocanusa Reservoir using a motor boat during the period of mid-December 2003 to July 2005, which spanned two burbot spawning seasons. Six (15%) tagged burbot were never relocated after release, and an additional seven (17.5%) of the tagged burbot either died or shed their tag within 60 d after release. We relocated 34 marked burbot (85%) on at least three occasions (mean = 10.0). Burbot frequently used the deepest portions of the reservoir, especially during the summer months. We estimated that the mean 50%, 75%, and 90% kernel home ranges were 14.6, 22.6 and 32.3 km², respectively. We found no evidence that burbot home range differed within the 2 years of this study. Although we did observe burbot moving a maximum distance of up to 64.3 km, we were unable to discern any general movement patterns by month or capture location. Individual burbot tagged in this study had relatively high fidelity to the original capture side of the reservoir, and almost half of our marked burbot were never relocated on the opposite side of the remnant Kootenai River thalweg, and those that did cross the thalweg do so infrequently. One burbot was entrained through Libby Dam approximately 134–276 d after capture and tagging.

Burbot: Ecology, Management, and Culture

Abstract.—Burbot <em>Lota lota </em>meat is nutritious and low in fat, and burbot liver oil is high in vitamins. However, burbot is not popular as a food fish in much of North America due to its appearance and because the meat has a relatively short shelf life. We present results from sensory panels on fried burbot meat that had been frozen and stored for 5 months with three methods: (1) dipping meat in liquid nitrogen, followed by storage at –80°C; (2) direct storage at –80°C; and (3) direct storage at –18°C. Panelists scored fried samples for tenderness, juiciness, fishy flavor, and overall desirability. In addition, texture (peak force at maximum compression and work performed) and color (lightness and a- and b-hues) of uncooked, defrosted meat (anterior and posterior sections, with and without skin removed) were measured instrumentally. Fried samples that had been directly stored at –80°C were scored by panelists as most tender, most juicy, and most desirable overall. Panelists also scored fried samples that had been directly stored at –80°C as less fishy tasting than samples frozen at –18°C. Freezing method, section of fillet, and presence/absence of skin had no effect on either texture variable or on any color variable measured. Posterior sections of burbot meat had higher levels of a-hue and b-hue than anterior sections. The relatively intermediate values of overall desirability combined with the results from other studies suggest that prepared products from frozen burbot meat may be better suited for commercial sale than frozen fillets.

Burbot: Ecology, Management, and Culture

<em>Abstract</em>.— Burbot <em>Lota lota </em>are the only freshwater members of the cod family Gadidae and possess a circumpolar distribution. Studies of phylogenetic relationships between palearctic and nearctic burbot have demonstrated the presence of distinct groups between North American and European populations. Higher resolution separation within western North American populations has thus far not been undertaken. In this study, we examined 372 burbot collected from 28 sample locations across its range in western North America. A 572 base pair portion of the mitochondrial cytochrome b gene was used to estimate diversity and divergence among populations and further characterize matrilineal lines. Three distinct haplogroups of burbot were observed that correspond to past allopatric distributions within Pleistocene refugia, namely the Pacific, Mississippi, and Missouri. Within the Columbia/Kootenai River basins west of the Continental Divide, admixtures of Pacific and Mississippi matrilines are indicative of both postglacial expansion and sorting as well as clinal variation resulting from vicariant events as seen in the Kootenai River population below Kootenai Falls. The study was also designed to help determine which northwest population would be most suitable in genetic terms as a donor stock to rehabilitate the Kootenai River, Idaho population. Of eight haplotypes found in the Kootenai River, Idaho and Columbia Lake, British Columbia, six are shared.

Burbot: Ecology, Management, and Culture

Abstract.—Movements of 11 sonic tagged burbot <em>Lota lota </em>were examined in the Kootenai River, Idaho, USA and Kootenay River and Kootenay Lake, British Columbia, Canada through up to three spawning seasons. Our objectives were to determine seasonal movements, differences in behavior of individual burbot, and the role of temperature and discharge on prespawn movement. Burbot demonstrated multiple movement patterns: 3 burbot were very mobile, 3 appeared to be intermediate in activity, and 5 were sedentary in summer, while 2 of the 11 entered Kootenay Lake and returned to the river. Most burbot began in autumn what may have been prespawn migrations when river temperatures fell to a range of 3.0–4.9°C. Six burbot entered the Goat River during the spawning season, of which five showed a multiple-year pattern of fidelity, and four returned to an apparent home pool and then exhibited sedentary behavior until the following winter. Three of the 11 burbot demonstrated an apparent nonspawning or rest year, but this was thought to be habitat-related. Logistic regression analysis of three of the six fish entering the Goat River suggested their migration to be best correlated to decreasing temperature and discharge. If the logistic model were representative of the population, then predicted migrations of burbot to the Goat River during winter would have followed a consistent pattern in November preLibby Dam, while postLibby Dam showed migrations to be unpredictable. Results of this study suggest that burbot had multiple life history patterns and several spawning locations and that rehabilitation measures should promote cooler winter water temperatures less than 5°C and discharges less than 300 m³/s.

Burbot: Ecology, Management, and Culture

Abstract.<em>—</em>Our objectives were to study habitat use of different life stages of the burbot <em>Lota lota </em>L. in lowland rivers and to develop habitat models to assess possible reintroduction sites in Flanders, Belgium. Summer habitat use of subadult and adult burbot was studied in lowland rivers in northeast France in the Meuse basin. Highest burbot densities were found in the upper river parts over several watersheds. Adult and subadult burbot showed a strong preference for microhabitats characterized by undercut banks and cover by tree roots. Habitat use of larvae and fingerlings was studied in spring. Both larvae and fingerlings were exclusively found in small tributaries (width < 2 m). Fingerlings mainly occupied tributaries with low to moderate flow velocity (0.05–0.15 m/s) and high densities of vegetation (>25%). Winter spawning migration was studied using fyke nets. Adult burbot migrated into the deepest tributaries and upstream migration was highest at increased water levels or flows. Analysis of water quality requirements revealed that both nitrate (NO₃^–) and total nitrogen (N_<em>t</em>) content negatively influenced burbot densities. With these results, two models to evaluate habitat suitability of lowland rivers for burbot were developed and tested. The use of these models to evaluate potential reintroduction sites for burbot in Belgium is discussed.

Burbot: Ecology, Management, and Culture

Abstract.—We examined the status and population characteristics of Kootenai River burbot <em>Lota lota </em>using capture–recapture data from 1993 to 2004. Our objective was to determine when this population may become functionally extinct and to help guide conservation efforts. A total of 403 burbot were captured, of which 300 were tagged and released, 31 were not tagged, and 72 were recaptures of fish tagged up to 4 years prior. Hoop-net catch per unit effort, where one unit of effort is a hoop-net set for 24 h, declined from 0.054 in 1996 to 0.008 in 2004. Mean total length of sampled burbot increased at a rate of about 8 mm/year from 1993 (516 mm) to 2004 (629 mm). Two models were developed for capture–recapture analysis, one that included effort data through a series of river reaches and one without effort data. The effort model appeared to be more reliable and suggested an average annual mortality rate for adult burbot (>250 mm) of 63%, an average annual recruitment of 77 fish, and an average estimate of 148 burbot in the Kootenai River from 1996 through 2004. Average declines in recruitment and population abundance were estimated to be 21% and 14% per year, respectively, resulting in estimates of only 20 recruits and a population size of only 50 burbot in 2004. These data confirm that Kootenai River burbot are in serious decline and may have already reached functional extinction. We conclude that immediate remedial measures must be implemented by focusing on rehabilitation of the native genetic stock and habitat remediation described in other studies.

Burbot: Ecology, Management, and Culture

<em>Abstract.</em>—Although burbot <em>Lota lota </em>are native to Montana, little is known about their distribution, life history, and ecology. The objectives of this study were to determine the distribution, relative abundance, and population characteristics of burbot in the upper Missouri River basin in north-central Montana, and to compare sampling efficiency of hoop nets, cod traps, and slat traps. Hoop nets and cod traps were fished in the Missouri River during March 2005 and 2006, and slat traps were fished during March 2006. In total, hoop nets were fished 572 net nights, cod traps for 94 net nights, and slat traps for 92 net nights. Catch rates of hoop nets and cod traps were higher in 2005 than in 2006, and catch rates of all gear types were higher in the upstream half of the study area. Mean section-wide hoop-net catch rates exhibited a significant (<EM>P </EM>≤0.05) inverse relationship with increasing distance downstream from Holter Dam, while catch rates for other gear types did not. Catch rates were not significantly different (<EM>P </EM>≥0.05) among gear types. The size (length and weight) and condition (relative weight) of burbot sampled was significantly (<EM>P </EM>≤0.05) different among gear types. Length, weight, and relative weight were higher for burbot sampled in hoop nets and cod traps than those sampled in slat traps. Slat traps were effective at sampling small (≤300 mm) burbot. Although most (80%) burbot were recaptured within 10 km of where they were tagged, three burbot moved more than 33 km. We hypothesize that the distribution of burbot in our study reach has changed and relative abundance has increased due to the cumulative effect of upstream reservoirs (Canyon Ferry, Hauser, and Holter) by decreasing the downstream water temperature regimen.

Burbot: Ecology, Management, and Culture

<em>Abstract.</em>—The freshwater gadoid, burbot <em>Lota lota</em>, was the subject of a captive breeding program to produce larvae for reintroduction into natural waters of Flanders, Belgium. Burbot broodfish were collected in 2002 from a river in France and maintained in earthen ponds at the Fish Research Center of the Research Institute for Nature and Forest in Linkebeek, Belgium. Each winter, they underwent gonadal maturation. In October, the mature fish were transferred to stocking ponds and fed with live fish. From the middle of December, they were exposed in indoor tanks to a continuous coldwater temperature of 4°C and a simulated natural light regime. This way, natural spawning could be induced without hormonal treatment. Between 582,766 and 984,963 eggs/kg bodyweight were collected from individual fish. Eggs averaged 1.00 mm in diameter. After fertilization, hatching started around day 32–33 when incubated at about 4°C (i.e., between 128 and 132 degree-days). Seventeen days later, at about 4°C, the larvae filled their swim bladder. A few days later (on day 21–24 posthatching when kept on 4°C), the larvae started exogenous feeding. The freshwater rotifer <em>Brachionus calyciflorus</em> proved to be an adequate starter food for growing burbot larvae but had to be replaced by larger food organisms like <em>Artemia </em>after 7–8 d. Burbot larvae were grown to one-summer-old juveniles (average survival 4%, average length 10 cm) in rearing ponds. The survival rate of the juvenile burbot in the ponds after 9 months was higher when the larvae were prefed with rotifers and <em>Artemia</em> prior to stocking in the ponds (survival up to 28% when fed for 18 d prior to the stocking).