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The recommendation of mid-ocean exchange of ballast water has resulted in significant release of aquatic invasive species in shelf areas. This paper describes a semiquantitative risk assessment model developed for dispersion of ballast water organisms in shelf seas. The model simulates ballast water exchange as the release of tracer into the surface layer of a circulation model of the Scotian Shelf and Gulf of Maine. Three metrics are proposed to describe the risk of invasion: (i) the time-integrated concentration at a given location (the cumulative exposure index); (ii) the time taken for organisms to reach a given area (the invasion time); and (iii) the onshelf average concentration. A risk equation is derived that computes the relative overall risk of invasion for exchange segments along vessel tracks. Model results confirm the choice of offshelf alternate ballast water exchange zone advised by Department of Fisheries and Oceans, Canada. Low risk segments tend to be adjacent to one another. A four-to eight-fold reduction in invasion risk is possible, although this is likely a lower bound because of the use of monthly mean velocity fields. The model can be run in an operational mode to provide real-time risk assessment for vessel ballast water exchange. [ABSTRACT FROM AUTHOR]

Walleye ( Sander vitreus) populations are cyclic because of biotic and abiotic factors, and wind activity, wave energy, and water levels may be influential given walleye spawn close to shore. We installed an anemometer and tridirectional velocimeter on a spawning reef in Big Crooked Lake, Wisconsin, in 2005 to determine wind-wave relationships and wave energy exceedance of critical velocities of both egg (affecting transport) and substrates (affecting abrasion or burial). To evaluate egg movement, we delineated egg locations at adhesive, postspawn, and black-eyed stages and surveyed on-shore for stranded eggs. We monitored water level with a staff gauge. Wind and wave velocities were significantly ( p < 0.01) correlated, and wave velocities were significantly higher ( p < 0.01) nearshore (2.0 m) than further from shore (4.6 m). Mean nearshore wave velocities were often sufficient to initiate movement of nonadhesive eggs (45% of records) and fine sand (39%) during egg incubation. Surveys indicated waves moved eggs closer to shore and some onto shore. Water level fluctuations (range = 2.4 cm) likely did not strand or desiccate eggs. We documented that wind and wave activity transports eggs and substrates and should be considered a critical factor in annual walleye egg survival and year-class strength. [ABSTRACT FROM AUTHOR]

The article discusses Northern shrimp (Pandalus borealis) represents one of the most important fisheries in the Northwest Atlantic Ocean. Topics include investigated potential larval dispersal among North Atlantic Fisheries Organization (NAFO) divisions; and found a largely stable, stream-like larval connectivity system driven by the main currents that flow over both the Greenland and Canadian continental shelves.

Estimating the distribution of water across the landscape is critical to understanding how local aquatic biogeochemical processes may upscale to regional or continental scales. Whereas technology to estimate the areal extent of inland waters has improved dramatically, predictions of lake bathymetry still rely primarily on correlations with lake area that lack a mechanistic underpinning. Using topographically diverse regions of Quebec (Canada), we developed a model for predicting lake volume and depth that relies on geographic data that are widely available, which can be easily adapted to other regions. We found that the average change in relief between the surrounding terrestrial landscape and the lake surface to be the best predictor of bathymetric properties (lake volume, lake depth). Unlike previous models, our method provides a clear mechanistic link between relief outside and within the perimeter of a lake that is supported by basic geographic principles. This model will be useful in estimating the volumetric distribution of water as well as the distribution of lake depth, which are integral to our understanding of biological and geochemical lake processes. [ABSTRACT FROM AUTHOR]

Extremes of flow and patterns of flow variability limit the distribution and abundance of riverine species via a natural disturbance regime. Using a habitat template approach, we describe the distribution and characteristics of natural flow regimes in Canada based on the severity of flows, flow predictability, and flow variability. Bayesian clustering was used to group 888 gauged watersheds across Canada into 10 classes. Some flow classes were found in all provinces, whereas others showed greater regional grouping related to land physiography (e.g., Canadian Shield and ecozones). Ontario and British Columbia had the greatest diversity of flow classes. Larger river systems tended towards less harsh flow regimes and greater flow regularity than small systems. A stream-lake network pattern, particularly the presence of lakes, decreased the severity of flow. The flow metric flood-free interval was found to be a potentially misleading indicator of reduced disturbance for high-latitude streams in Canada where ice formation and persistence are important stress factors for biota. Most flow stations had an 80% or higher chance of belonging to their primary membership class. Quantifying uncertainty in class assignment can help fellow scientists and resource managers appropriately apply our findings. [ABSTRACT FROM AUTHOR]

We sought to quantify the possible population-level influence of sediment plumes and algal blooms on yellow perch ( Perca flavescens), a visual predator found in systems with dynamic water clarity. We used an individual-based model (IBM), which allowed us to include variance in water clarity and the distribution of individual sizes. Our IBM was built with laboratory data showing that larval yellow perch feeding rates increased slightly as sediment turbidity level increased, but that both larval and juvenile yellow perch feeding rates decreased as phytoplankton level increased. Our IBM explained a majority of the variance in yellow perch length in data from the western and central basins of Lake Erie and Oneida Lake, with R2 values ranging from 0.611 to 0.742. Starvation mortality was size dependent, as the greatest daily mortality rates in each simulation occurred within days of each other. Our model showed that turbidity-dependent consumption rates and temperature are key components in determining growth and starvation mortality of age-0 yellow perch, linking fish production to land-based processes that influence water clarity. These results suggest the timing and persistence of sediment plumes and algal blooms can drastically alter the growth potential and starvation mortality of a yellow perch cohort. [ABSTRACT FROM AUTHOR]

Advection of teleost early life stages from nursery habitats can greatly impact year-class strength. Few studies test the effects of current on retention in freshwater fish eggs and larvae, so we used walleye ( Sander vitreus) to assess current effects throughout egg and larval development and the role of substrate on egg retention. Eggs were removed from sand substrates at currents of 12 cm·s-1, but much higher speeds were required for removal from tile or stones. Larvae exhibited biphasic swimming ability, with slow swimming below 21 mm total length and rapidly increasing ability above 21 mm. These data necessitate adjusting models currently used to link water current and nursery advection in this and similar species, as the current effects were clearly substrate- and size-dependent. [ABSTRACT FROM AUTHOR]

Upwelling ecosystems are particularly heterogeneous and present intense mesoscale (tens of kilometres) and submesoscale (hundreds of metres to kilometres) activity that are expected to drive the distribution of the organisms and thus their interactions. Here we addressed the impact of the physical forcing in the northern Humboldt Current system off Peru, which is characterized by the presence of an intense and shallow oxygen minimum zone and used the variability of the depth of the oxycline as a proxy of the physical forcing that impacts the epipelagic communities. We analyzed simultaneous high-resolution acoustic observations of the oxycline depth, the biomass in macrozooplankton, and the biomass in pelagic fish. Three complementary methodologies were considered: ( i) geostatistical methods and correlation tests, ( ii) principal coordinates of neighbour matrices, and ( iii) wavelet analysis. Our results highlight the relevance of a multimethod framework to characterize the multiscale relationships between marine ecosystem components. We also provided evidence that the submesoscale-to-mesoscale variability of the oxycline depth drives the distribution of macrozooplankton, which further structures the distribution of forage fish in a bottom-up cascade. [ABSTRACT FROM AUTHOR]

An individual-based model, incorporating outputs of a data-assimilating hydrodynamic model, was developed to investigate the role of ocean circulation in the recruitment processes of western rock lobster () during its 9- to 11-month larval phase off the west coast of Australia. During austral summer, strong northward alongshore winds aid the offshore movement of early-stage model larvae from midshelf hatching sites into open ocean; during austral winter, eastward flows that feed the enhanced Leeuwin Current facilitate onshore movement of late-stage larvae towards nearshore habitats. Stokes drift induced by swells from the Southern Ocean is critical to retain larvae off the west coast. Diurnal migration and temperature-dependent growth are also important. Model larvae hatched in late spring - early summer grow faster because of longer exposure to warm summer temperature, which allows them to be transported towards the coast by the strong onshore flows in winter and reduces their natural mortality. Preliminary source-sink relationship indicates that the population was well mixed off the coast, with higher likelihood of settlement success from hatching sites in the north, mostly due to higher surface temperature. Weighted with the breeding stock distribution, the area between 27.5°S and 29.5°S, including the Abrolhos Islands, is the most important hatching area to the success of settlement. [ABSTRACT FROM AUTHOR]