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Stapanian M.A.,U.S. Geological Survey | Paragamian V.L.,885 W. Kathleen Avenue | Madenjian C.P.,U.S. Geological Survey | Jackson J.R.,Cornell Biological Field Station | And 3 more authors.
Fish and Fisheries | Year: 2010

Although burbot (Lota lota Gadidae) are widespread and abundant throughout much of their natural range, there are many populations that have been extirpated, endangered or are in serious decline. Due in part to the species' lack of popularity as a game and commercial fish, few regions consider burbot in management plans. We review the worldwide population status of burbot and synthesize reasons why some burbot populations are endangered or declining, some burbot populations have recovered and some burbot populations do not recover despite management measures. Burbot have been extirpated in much of Western Europe and the United Kingdom and are threatened or endangered in much of North America and Eurasia. Pollution and habitat change, particularly the effects of dams, appear to be the main causes for declines in riverine burbot populations. Pollution and the adverse effects of invasive species appear to be the main reasons for declines in lacustrine populations. Warmer water temperatures, due either to discharge from dams or climate change, have been noted in declining burbot populations at the southern extent of their range. Currently, fishing pressure does not appear to be limiting burbot populations world-wide. We suggest mitigation measures for burbot population recovery, particularly those impacted by dams and invasive species. Published 2010. This article is an US Government work and is in the public domain in the USA.

Watkins J.,Cornell Biological Field Station
Aquatic Ecosystem Health and Management | Year: 2010

Satellite-based sensors provide synoptic measurements of surface parameters useful in detecting physical and biological conditions of the Great Lakes. Satellite surface temperature measurements using infrared spectra are compatible with buoy measurements and the time series now covers more than two decades in length. This time-series tracks seasonal warming patterns and localized upwelling events. The use of visible spectra for remote sensing of water clarity and particle composition is improving with new algorithms to separate chlorophyll-a, inorganic particles, and dissolved organic matter. The use of satellites to measure these variables holds promise for future quantification of phytoplankton production, calcite precipitation (whiting), and suspended sediment from rivers and resuspension events. Satellite imagery has also been useful for interpreting ship-collected data such as those associated with the bi-national Lake Ontario Lower Foodweb Assessment (LOLA) in 2003. © 2010 AEHMS.

Johannsson O.E.,Canadian Department of Fisheries and Oceans | Bowen K.L.,Canadian Department of Fisheries and Oceans | Holeck K.T.,Cornell Biological Field Station | Walsh M.G.,U.S. Geological Survey
Canadian Journal of Fisheries and Aquatic Sciences | Year: 2011

We investigated population responses of Mysis to ecosystem changes induced by invasion of dreissenids and predatory cladocerans, Cercopagis and Bythotrephes. Lake productivity declined as dreissenids invaded the offshore region. Whole-lake mysid biomass was compared before (early 1990s) and after (2002-2007) the invasion period; it declined 40%- 45%. Abundance of young mysids and presence of a summer cohort increased with summer, epilmnetic, nighttime zooplankton biomass (i.e., food biomass index). Cercopagis + Bythotrephes biomass was negatively correlated with this index, implicating them in the mysid decline. Eggs per gravid female increased with autumn, total-water-column zooplankton biomass, reflecting the greater use of hypolimnetic waters by adults. Reproductive success was below replacement during the period 2002-2005. First-year mysid growth rate was maintained while population abundance declined, suggesting selection for individuals that feed effectively at low food concentrations. Mortality rates in the first and second years were dependent on cohort density, indicating that competition for food limited abundance in the first 2 years. Fish predation indices (smelt and alewife combined) were correlated positively with mortality rates and negatively with abundance in the third year. Thus, mysids cannot support as many fish in invaded compared with non-invaded lakes. They may also not be a stable food resource; unusual cohort losses occurred in some years.

Karatayev A.Y.,Buffalo State College | Burlakova L.E.,Buffalo State College | Burlakova L.E.,State University of New York at Buffalo | Mastitsky S.E.,Buffalo State College | And 3 more authors.
Journal of Shellfish Research | Year: 2011

Examining congeners can help identify critical differences between species that affect invasion and spread. We examined Dreissenapolymorpha (zebra mussel) and Dreissena rostriformis bugensis (quagga mussel), which are important invaders in freshwater and share general ecological characteristics, to determine whether they had similar rates of invasion at different spatial scales (global, regional, local, and individual water bodies) from the time of first introduction to the present. We also contrasted differences in ecological and population characteristics that could influence speed of spread. Although D. polymorpha and D. r. bugensis are relatives and share a common native habitat, morphology, lifestyle, life history, and dispersal potential, D. polymorpha was found to be a better invader than D. r. bugensis at most spatial scales throughout their invasion history. Spread at the regional scale in North America was the same for both species, but the initial rate of invasion by zebra mussels far outpaced the spread of quagga mussels both in the United States and in Europe. The estimated lag time between initial introduction and maximal population size is 5 times shorter for D. polymorpha than for D. r. bugensis, which may be an important factor affecting the speed with which this species can spread. Differences in population dynamics may facilitate the increased rates of spread of D. polymorpha relative to D. r. bugensis, especially at smaller spatial scales.

Kocovsky P.M.,U.S. Geological Survey | Rudstam L.G.,Cornell Biological Field Station | Yule D.L.,U.S. Geological Survey | Warner D.M.,U.S. Geological Survey | And 6 more authors.
Journal of Great Lakes Research | Year: 2013

Standardized methods of data collection and analysis ensure quality and facilitate comparisons among systems. We evaluated the importance of three recommendations from the Standard Operating Procedure for hydroacoustics in the Laurentian Great Lakes (GLSOP) on density estimates of target species: noise subtraction; setting volume backscattering strength (Sv) thresholds from user-defined minimum target strength (TS) of interest (TS-based Sv threshold); and calculations of an index for multiple targets (Nv index) to identify and remove biased TS values. Eliminating noise had the predictable effect of decreasing density estimates in most lakes. Using the TS-based Sv threshold decreased fish densities in the middle and lower layers in the deepest lakes with abundant invertebrates (e.g., Mysis diluviana). Correcting for biased in situ TS increased measured density up to 86% in the shallower lakes, which had the highest fish densities. The current recommendations by the GLSOP significantly influence acoustic density estimates, but the degree of importance is lake dependent. Applying GLSOP recommendations, whether in the Laurentian Great Lakes or elsewhere, will improve our ability to compare results among lakes. We recommend further development of standards, including minimum TS and analytical cell size, for reducing the effect of biased in situ TS on density estimates. © 2013.

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