Incoming Tide Research Articles

Tide impacts the dispersion of eDNA from nearshore net pens in a dynamic high‐latitude marine environment

AbstractEnvironmental DNA (eDNA) is increasingly used to detect animals in aquatic habitats, but uncertainty remains about the relationship between the present location of an animal relative to eDNA detections. In marine environments, physical characteristics—such as tides and currents—can influence the distribution of eDNA. In this study, we make use of hatchery net pens containing >46 million juvenile chum salmon (Oncorhynchus keta) in nearshore Southeast Alaska to test for dispersion of eDNA and the effects of tide. Initially, we collected and filtered surface water every 80 m along a 2 km transect to test eDNA attenuation over surface distance during incoming and outgoing tides on a single day. The following year, we sampled at three depths (0 m, 5 m, and 10 m) every 500 m along the same transect as well as along a perpendicular transect, to understand dispersion by depth and in additional directions. Chum salmon eDNA was quantified using species‐specific qPCR. We found that surface samples showed a consistent signal of decreasing chum salmon eDNA across the 2 km transect (R2 = 0.665), with the majority of eDNA detections within 1.5 km of the net pens. Tide had a significant effect, resulting in higher concentrations of chum DNA throughout the transect during incoming tide and a steeper decline in eDNA over distance during outgoing tide (R2 = 0.759). Depth affected chum salmon DNA concentration, with the majority of eDNA at the surface and a decreasing amount of DNA with increasing depth. This study addresses one of the critical knowledge gaps in applying eDNA to marine fisheries management by providing empirical evidence of eDNA dispersion and demonstrating that most eDNA detections are likely from nearby individuals that are either currently or recently present. Yet even at close proximity, eDNA signal strength fluctuates and depends on the physical environmental variables during a given sampling event.

Tidal range electricity generation into the twenty-second century

Tidal range electricity generation schemes are designed to have a minimum operational life of at least 120 years, making it important to plan for changes such as sea-level rise (SLR). Earlier studies have shown that schemes can maintain the existing tidal range within the impoundment and protect areas from flooding. Here it is demonstrated that tidal range technology can maintain the current tidal extent despite SLR and suggests the operational strategies to achieve it. The approach is the only way to safeguard existing intertidal habitats. Mechanical and electrical plant requires a major overall, upgrade or replacement every 40 years; the levelised cost of energy is structured in 40-year periods reducing after the first period. Increasing the capacity or efficiency of the plant during the refits allows the protection of low-lying areas to be maintained and more electricity to be generated. The strategy requires energy to be used in pumping to achieve the current low tidal limits and the incoming tide to be curtailed to maintain the high tide extent, but there is very little effect on annual electricity production. Flexible operation can offer some protection from riverine flooding and existing inundation cycles can be maintained.

Adaptation and Survival of Marine-Associated Spiders (Araneae).

Aquatic environments are an unusual habitat for most arthropods. Nevertheless, many arthropod species that were once terrestrial dwelling have transitioned back to marine and freshwater environments, either as semiaquatic or, more rarely, as fully aquatic inhabitants. Transition to water from land is exceptional, and without respiratory modifications to allow for extended submergence and the associated hypoxic conditions, survival is limited. In this article, we review marine-associated species that have made this rare transition in a generally terrestrial group, spiders. We include several freshwater spider species for comparative purposes. Marine-associated spiders comprise less than 0.3% of spider species worldwide but are found in over 14% of all spider families. As we discuss, these spiders live in environments that, with tidal action, hydraulic forces, and saltwater, are more extreme than freshwater habitats, often requiring physiological and behavioral adaptations to survive. Spiders employ many methods to survive inundation from encroaching tides, such as air bubble respiration, airtight nests, hypoxic comas, and fleeing incoming tides. While airway protection is the primary survival strategy, further survival adaptations include saltwater-induced osmotic regulation, dietary composition, predator avoidance, reproduction, locomotory responses, and adaptation to extreme temperatures and hydrostatic pressures that challenge existence in marine environments.

Waiting for the right time and tide: The fine‐scale migratory behavior of river herring in two coastal New England streams

AbstractObjectiveAlewife Alosa pseudoharengus and Blueback Herring A. aestivalis, collectively referred to as river herring, are anadromous clupeids inhabiting the North American Atlantic coast. Although the seasonal patterns of their spawning migration are well studied and predictable, the fine‐scale movements are still poorly resolved.MethodsThis study used high‐resolution acoustic imaging to study the fine‐scale behavior of river herring during their spring spawning migration in two coastal rivers in Massachusetts, United States.ResultObservations suggest that seasonal patterns of migration appear to be influenced by temperature, while fine‐scale patterns in migration were associated with the time of day, tidal state, and their interaction. River herring were consistently observed during both day and night, with elevated peaks of activity in the early morning and late afternoon. Daytime movement consisted of the intermittent passage of large, dense schools, while nighttime movement consisted of the frequent passage of individuals or small groups. The highest numbers of herring observations were associated with flood and high tides. Additionally, the interactions between time of day and tidal state resulted in synergistic positive effects during crepuscular incoming tides, which were favorable to movement, and synergistic negative effects during midday low tides, which inhibited fish movement.ConclusionThe changing relationship between the time of day and tidal state within the season manifested in changing periodicity in fish movement to correlate with favorable movement conditions. Since movements may be related to both time of day and tide, previous run size estimates from visual counts made only during the day may be too low. Sampling methodologies that collect information during all 24 h would likely produce the most accurate run size estimates. This study highlights the need to view river herring migration in a holistic context predicated by multiple environmental and biological factors that vary at several temporal scales (i.e., seasonally, daily, and hourly).

Asymmetric evolution of river mouth bifurcation under angled river‐tide interaction, a case study at river mouths of Lingding Bay, Pearl River estuary

AbstractA thorough understanding of the evolutionary trends of river bifurcation channels is crucial for effective estuarine management in China's Greater Bay Area due to significant morphological changes observed in river mouth channels. At this tide‐influenced river mouth, where suspended sediment transport is dominant, how river mouth bifurcated channels that have different angles to the major axis of the incoming tidal flow in the receiving basin evolve on decadal scales remains unclear. Based on a comparative analysis of historical bathymetric data and numerical experiments using a validated morphodynamic model, we developed a conceptual model to illustrate the two end members of the morphological evolution of river mouth channels: a low‐angle (<45°) main channel and a high‐angle (>45°) secondary channel relative to the major axis of tidal flow in the receiving basin. If the mouth outflow also has a low angle with the main channel, the incoming tidal discharge fluxes have first‐order control over changes in the evolutionary trend of the bifurcated channels by changing the partition of residual sediment discharges between the two bifurcated channels. For example, a high incoming tidal discharge that varies around the mean flow increases the partitioning of residual sediment discharges from the upstream channel to the low‐angle channel, facilitating tide‐induced erosion in the low‐angle channel. By contrast, a low incoming tidal discharge decreases the partitioning of residual sediment discharges from the upstream channel to the low‐angle channel, which facilitates fluvial‐induced erosion in the high‐angle channel. Thus, high tidal discharges usually coincide with the river mouth adopting a single channel, and low tidal discharges facilitate the formation of fluvial‐induced bifurcation. The historical evolution of the river mouth and modern velocity measurements corroborated results derived from model experiments. The conceptual model applies to river mouths where suspended sediment transport is dominant and influenced by angled incoming tides.

Habitat use across the tidal cycle by black-headed gulls breeding in the Wadden Sea

Movements of birds foraging in intertidal areas are often strongly linked to the tidal cycle, as water levels determine where and when birds can forage. The strength of this link likely depends on the ability to forage in habitats other than intertidal areas and on constraints imposed by breeding duties. Few studies have focused on the use of intertidal areas by generalists, such as the black-headed gull Chroicocephalus ridibundus, that occupy a wide variety of habitats within and beside intertidal mudflats. We investigated to what degree black-headed gulls (1) use intertidal mudflats versus terrestrial habitats during different phases of the tidal cycle, (2) follow the tidal wave to exploit recently exposed mudflats and (3) whether these behaviours are influenced by central place foraging. For this, 11 black-headed gulls breeding on the Wadden Sea island Griend were tracked during two years using GPS loggers. When commuting to and from Griend, up to 75% of their time was spent in intertidal areas during low and incoming tide, which increased to 92% when not behaving as central place foragers. While their movements were strongly linked to the tidal cycle, they did not follow the tidal wave across the tidal basin during either period. Rather, individuals foraged either predominantly west or east of Griend during low and incoming tide and mostly remained visiting these areas when not behaving as central place foragers. As one of the most abundant species in the Wadden Sea, the extensive use of intertidal mudflats highlights the importance of black-headed gulls within the intertidal food web of the Wadden Sea.

The Use of Transport Time Scales as Indicators of Pollution Persistence in a Macro-Tidal Setting

An understanding of water exchange processes is essential for assessing water quality management issues in coastal bays. This paper evaluates the impact of water exchange processes on pollution persistence in a macro-tidal semi-closed coastal bay through two transport time scales (TTS), namely residence time and exposure time. The numerical model was calibrated against field-measured data for various tidal conditions. Simulated current speeds and directions were shown to agree well with the field data. By considering different release scenarios of a conservative tracer by the refinement of an integrated hydrodynamic and solute transport model (the EFDC), the two TTS were used for interpreting the water exchange processes in a semi-closed system, and for describing the effects of advective and dispersive processes on the transport and fate of pollutants. The results indicate that the magnitudes of river inflows to the bay, tidal ranges, and tracer release times significantly influence the residence and exposure times. Return coefficients were shown to be variable, confirming the different effects of returning water for the different conditions that were studied. For the tested river flow magnitudes and tide conditions, the exposure times were generally higher than the residence times, but particularly so for neap tide conditions. The results, therefore, highlight the risks associated with pollutants leaving a specified domain on an outgoing tide but re-entering on subsequent incoming tides. The spatial distributions of the exposure and residence times across the model domain confirmed that for the case of Dublin Bay, river inputs have a potentially greater impact on water quality on the northern side of the bay.

Crabs ride the tide: incoming tides promote foraging of Giant Mud Crab (Scylla serrata)

BackgroundEffective fisheries management of mobile species relies on robust knowledge of animal behaviour and habitat-use. Indices of behaviour can be useful for interpreting catch-per-unit-effort data which acts as a proxy for relative abundance. Information about habitat-use can inform stocking release strategies or the design of marine protected areas. The Giant Mud Crab (Scylla serrata; Family: Portunidae) is a swimming estuarine crab that supports significant fisheries harvest throughout the Indo-West Pacific, but little is known about the fine-scale movement and behaviour of this species.MethodsWe tagged 18 adult Giant Mud Crab with accelerometer-equipped acoustic tags to track their fine-scale movement using a hyperbolic positioning system, alongside high temporal resolution environmental data (e.g., water temperature), in a temperate south-east Australian estuary. A hidden Markov model was used to classify movement (i.e., step length, turning angle) and acceleration data into discrete behaviours, while also considering the possibility of individual variation in behavioural dynamics. We then investigated the influence of environmental covariates on these behaviours based on previously published observations.ResultsWe fitted a model with two well-distinguished behavioural states describing periods of inactivity and foraging, and found no evidence of individual variation in behavioural dynamics. Inactive periods were most common (79% of time), and foraging was most likely during low, incoming tides; while inactivity was more likely as the high tide receded. Model selection removed time (hour) of day and water temperature (°C) as covariates, suggesting that they do not influence Giant Mud Crab behavioural dynamics at the temporal scale investigated.ConclusionsOur study is the first to quantitatively link fine-scale movement and behaviour of Giant Mud Crab to environmental variation. Our results suggest Giant Mud Crab are a predominantly sessile species, and support their status as an opportunistic scavenger. We demonstrate a relationship between the tidal cycle and foraging that is likely to minimize predation risk while maximizing energetic efficiency. These results may explain why tidal covariates influence catch rates in swimming crabs, and provide a foundation for standardisation and interpretation of catch-per-unit-effort data—a commonly used metric in fisheries science.

Tidal cycle and time of day control pH levels in coastal habitats of the western Indian Ocean: the case of Mnazi and Chwaka Bays in Tanzania

Ocean acidification, a progressive decrease in the pH and change in the carbonate chemistry of seawater caused by the uptake of carbon dioxide (CO2) from the atmosphere, is a growing crisis that threatens marine species. pH data relevant to a species’ natural habitat in the coastal waters of the western Indian Ocean (WIO) is still sparse, limiting the capacity to undertake manipulative studies to better understand the impacts of ocean acidification on marine species. This study investigated tidal and day-night pH variations in mangrove, seagrass, and coral reef habitats of the WIO by using Tanzania as a case study. The mean pH of the studied coastal habitats was highest in seagrass (8.49 ± 0.29), followed by coral reef (8.33 ± 0.06), and lowest in mangrove (8.20 ± 0.17). Seagrass habitats had the highest pH (9.06) during the day at low spring tides, mangrove habitats had the highest pH (8.45) during the day at high spring tides, and coral reef habitats had the highest pH (8.47) during the day at low tides. Seagrass habitats had the widest pH range (1.03), followed by mangrove habitats (0.54), while coral reef habitats had the narrowest range (0.23). The water with the highest pH during the day was transported to nearby mangrove habitats during incoming tides and to coral reef habitats during outgoing tides, resulting in the highest mean pH in mangrove and coral reef habitats during spring high and low tides, respectively. pH within the seagrass habitats correlated strongly and positively with changes in temperature (r=0.80), dissolved oxygen (r=0.84), and salinity (r=0.72), while pH in mangrove habitats correlated moderately and positively with dissolved oxygen (r=0.59). This study provides in-situ evidence on the pH fluctuations in the WIO’s coastal habitats over time and space, with water from seagrass habitats capable of raising the pH of water in nearby mangrove and coral reef habitats during the day, thereby potentially helping in the mitigation of the effects of ocean acidification on these habitats.

Incoming tide by Astrid Dehe and Achim Engstler, translated by Rachel Farmer

<i>Incoming tide</i> by Astrid Dehe and Achim Engstler, translated by Rachel Farmer

The Incoming Tides That Lift the Boats: Growth through Heterogeneous Convergence in Chinese Provinces

The Incoming Tides That Lift the Boats: Growth through Heterogeneous Convergence in Chinese Provinces

Computational Fluid Dynamics-based Simulation and Design of a Horizontal Tidal Turbine System

Tidal phenomena, the rhythmic rise and fall of sea waters due to gravitational forces among celestial bodies like the Sun, Earth, and moon, offer a dependable source of renewable energy. Tidal energy, with its predictability and high energy density, is an attractive sustainable option. Tapping into this energy requires a specialized device, the tidal turbine, where the rotor plays a vital role. The rotor converts the kinetic energy of incoming tides into useful mechanical energy, evaluated through thrust, torque, and power efficiency. This study focuses on designing a horizontal tidal turbine using a three-dimensional Computational Fluid Dynamics (CFD) model with ANSYS Fluent software. Input parameters are based on real-world measurements of the average current velocity of 1 m/s obtained using Acoustic Doppler Current Profiler (ADCP). The paper serves two purposes: validating the applied design approach and analysing crucial design factors. By confirming design compatibility and assessing factor properties, the research contributes to optimizing tidal turbine efficiency and its feasibility as a sustainable energy source.

Tidal bore impact pressures on a trestle pier in the Qiantang River Estuary, China

Tidal bores are natural phenomena resulting from the nonlinear distortion of tidal waves and propagate upstream with the incoming tide. The Qiantang River tidal bore is world-famous for its great momentum which can occasionally inflict major damage to infrastructures in the Qiantang River Estuary, China. Existing design guidelines are not fit for accurately estimating the tidal bore loads on elevated structures. This study investigated the impact of tidal bores on the trestle piers of a river-crossing bridge using field tests. Based on the measured data, empirical formulas for the maximum impact pressure in four zones across the trestle were derived, and the influence of the Froude number on the peak pressure was determined. Results show that the peak pressure of the instantaneous impulsive state of the bore can exceed the pressure of the quasi-steady state 10-fold. The maximum dynamic impact pressure on the seaward side of the pier occurs at the base of the bore. The peak dynamic pressure accounts for 54%, 45%, and 20% of the total pressure for Froude numbers of 1.26, 1.12, and 1.04, respectively. The results of this study can serve as valuable references for the load design of structures against tidal bores and tsunami-like waves.

Scheelite-type rare earth vanadates TVO4 (T = Ho, Y, Dy) electrocatalysts: Investigation and comparison of T site variations towards bifunctional electrochemical sensing application

In the wake of the recent COVID-19 pandemic, antibiotics are now being used in unprecedented quantities across the globe, raising major concerns regarding pharmaceutical pollution and antimicrobial resistance (AMR). In view of the incoming tide of alarming apprehensions regarding their aftermath, it is critical to investigatecontrol strategies that can halt their spread. Rare earth vanadates notable for their fundamental and technological significance are increasingly being used as electrochemical probes for the precise quantification of various pharmaceutical compounds. However, a comprehensive study of the role of the cationic site in tailoring the response mechanism is relatively unexplored. Hence, in this work we present a facile hydrothermal synthesis route of rare earth vanadates TVO4 (T = Ho, Y, Dy) as efficient electrocatalyst for the simultaneous detection of nitrofurazone (NF) and roxarsone (RX). There appears to be a significant correlation between T site substitution, morphological and the electrochemical properties of rare earth metal based vanadates. Following a comparative study of the electrochemical activity, the three rare-earth vanadates were found to respond differently depending on their composition of T sites. The results demonstrate that Dy-based vanadate displays increased electrical conductivity and rapid charge transfer characteristics. Thus, under optimal reaction conditions DyVO4- based electrodes imparts outstanding selectivity towards the detection of NF and RX with an extensive detection window of NF = 0.01–264 µM & RX = 0.01–21 µM and 36–264 µM and low detection limit (0.002, 0.0009 µM for NF and RX, respectively). In real-time samples, the proposed sensor reveals itself to be a reliable electrode material capable of detecting residues such as NF and RX.

Untangling the Gordian knot: estuary survival under sea-level rise and catchment pollution requires a new policy and governance approach

ABSTRACT Many estuaries are squeezed between sea-level rise, coastal hardening and adverse cumulative effects from unsustainable catchment activities. In Aotearoa New Zealand, there is little planning to provide future accommodation space for estuaries. A complex knot of policies and plans, and accompanying poor implementation also affect ecological sustainability. We examine these issues for Brooklands Lagoon/Te Riu o Te Aika Kawa, a tidal lagoon northeast of Christchurch/Ōtautahi. It is within the takiwā of Ngāi Tahu iwi and Ngāi Tūāhuriri hapū, and the jurisdictions of Christchurch City Council and Environment Canterbury. The estuary is influenced by three rivers, and surrounding land use is managed under three different statutory resource management plans, along with several non-regulatory strategies and organisational management plans. However, these plans are poorly integrated and estuarine ecological health is compromised. The incoming tide of resource management and local government reform will add complexity, but also an opportunity to accommodate and enhance the estuary as a blue carbon sink, and to restore cultural and ecological values. This requires specific recognition of estuaries in the proposed managed retreat and spatial planning laws, and within the replacement resource management statute. Legal recognition of Indigenous customary rights could also produce novel governance models to improve management.

Monetary policy in a world of radical uncertainty

Monetary policy in a world of radical uncertainty

Pathogenic Vibrio parahaemolyticus Increase in Intertidal‐Farmed Oysters in the Mid‐Atlantic Region, but Only at Low Tide

AbstractHuman‐pathogenic marine bacteria in the genus Vibrio proliferate rapidly in shellfish tissues when exposed to warm ambient air conditions, such as during intertidal exposure. However, it remains unclear whether intertidal‐cultured shellfish are inherently associated with elevated Vibrio concentrations. Here we spatially matched eastern oysters (Crassostrea virginica) held in subtidal and intertidal aquaculture systems at six experimental oyster farms along the mid‐Atlantic coast and tested whether intertidal aquaculture elevates concentrations of V. parahaemolyticus, the predominant species associated with seafood‐related gastroenteritis, as well as concentrations of V. parahaemolyticus carrying the tdh and/or trh genes associated with pathogenicity in humans. Across the sites and over time, we found only slight evidence for increasing V. parahaemolyticus concentrations with exposure to ambient air at low tide; however, tdh/trh+ V. parahaemolyticus increased about 1.5‐fold. We also found that total V. parahaemolyticus concentrations and concentrations of tdh/trh+ V. parahaemolyticus did not differ between intertidal‐ and subtidal‐cultured oysters when submerged at high tides. Any changes to V. parahaemolyticus concentrations within oyster tissues, including concentrations of tdh/trh+ V. parahaemolyticus, therefore diminish with the incoming tide. Our results collectively support the existing time‐to‐cooling restrictions that are in place in many state Vibrio control plans, which involve minimizing the amount of time harvested shellfish can be held prior to cooling or refrigeration, but oppose more austere measures such as restricting or prohibiting intertidal harvest entirely.

Population Size, Behavior and Threats to Indian Skimmers (Rhynchops albicollis) at Their Largest Known Wintering Site

Bangladesh hosts most of what is left of Indian Skimmer (Rhynchops albicollis) populations, a globally endangered species. Each October-March from 2015-2020, 21 surveys of nonbreeding birds were made in Nijhum Dweep National Park, Bangladesh. High tide or evening roosts were counted from vantage points whenever a buildup or breakdown of skimmer concentrations was noticed, and site use noted by marking all observations of presence and activity on maps. The largest single count was 3,108 skimmers on 18 February 2020, constituting 30-50% of the known global population. Indian Skimmers mostly occurred in Damar Char West and at the tip of the Majher Char. Throughout the day with incoming tide, skimmers moved between preferred roosting areas to forage in the shallows. We describe a unique group-foraging strategy in which skimmers chase fish from deep water to shallow water along the shoreline. Circling high over the tidal channel, the flock of skimmers dives down in unison to just above the water surface, then spreading like a net towards the shore. Raptors caused disturbances to roosting skimmers, and we observed one instance of predation of a skimmer by a White-bellied Sea Eagle (Haliaeetus leucogaster). Human fishing activities disturbed nearshore foraging and shoreline roosting skimmers. We suggest protecting Damar Char West by regulating human activities to minimize disturbance from December to March.

Modeling Tidal Characteristics in a Creek-Marsh Drainage System: Implications for Stormwater Management

The traditional goal of stormwater management is to reduce the threat of flooding to life and property, and so most landscapes are engineered to maximize the speed at which the unwanted water leaves the watershed. This has been effective in landscapes with some topographic gradient. This often involves the installation of drainage ditches that disperse runoff from urban areas to receiving water bodies; in coastal areas this means a tidal creek, estuary, bay, sounds, or the coastal ocean. This practice reduces flood hazards in some cases but results in unintended effects on the natural hydrology in the watershed and downstream tidal dynamics. For low-gradient watersheds in humid climates, ditch systems also lower the water table of an area, increasing infiltration to recharge and groundwater discharge to streams (baseflow), and larger volume of freshwater delivered downstream yearround. Ditches also create unintentional avenues for the incoming tide from a tidal creek or tidally-influenced waterway to reach further inland, thus reducing the hydraulic gradient between the inland areas and the receiving water body. The combination of these effects can exacerbate compound flooding events, increasing the flood probability if high tide and storm events coincide. Additionally, coastal communities face the challenge of mitigating more complicated flood hazards while land development increases to meet the needs of a growing population. This study analyzed the tidal influence within an inland drainage ditch in the central coast of South Carolina USA that is representative of thousands of artificially-drained coastal watersheds. The ditch-creek system investigated here is 12 km long in a 753-hectare (1860-acre) watershed of Church Flats Creek, a first-order tidal system. We monitored for 13 months a 0.75-km reach of the lower ditch portion of the system, just above the relatively undisturbed tidal creek and marsh. Prior to ditching in the 1960s this system had a wetland-rich floodplain but is now partially tidal. Field data collected were stream stage (depth), discharge, tidal range, tidal volume, incoming (flood) and outgoing (ebb) tidal durations, and water table hydrograph at a location about 50 m of mid-reach of the ditch. Multiple linear regressions were performed to best predict the flood and ebb tidal durations of the system based on tidal characteristics within the ditch. The mean values were 229 ± 2.5 and 182 ± 2.1 minutes for flood and ebb tide durations, respectively and the models explained 84% (residual standard error (RSE) of 25 minutes) and 80% (RSE of 23 minutes) for the flood and ebb conditions, respectively. The models were simulated for sea levels in 1993 and 2050, and results indicate that the flood tide within the drainage ditch is predicted to increase an average of 66 minutes and the total tidal duration (flood and ebb) an average of 139 minutes by 2050. These results suggest a loss in drainage functionality as sea level rises. Increases in the duration of tidal influence will induce a lower capacity for stormwater volume than the drainage infrastructure was constructed to manage, therefore resulting in an increased frequency of compound flooding events because of the lower storage volume and decreased hydraulic gradient in the system. This study fills a knowledge gap of tidal dynamics within coastal ditch-creek systems and we urge stormwater managers to consider the unintended consequences of using traditional stormwater methods in a region that does not benefit from gravity drainage practices like in other regions.

Sharks surf the slope: Current updrafts reduce energy expenditure for aggregating marine predators.

An animal's energy landscape considers the power requirements associated with residing in or moving through habitats. Within marine environments, these landscapes can be dynamic as water currents will influence animal power requirements and can change rapidly over diel and tidal cycles. In channels and along slopes with strong currents, updraft zones may reduce energy expenditure of negatively buoyant fishes that are also obligate swimmers. Despite marine predators often residing within high-current area, no study has investigated the potential role of the energetic landscape in driving such habitat selectivity. Over 500 grey reef sharks Carcharhinus amblyrhynchos reside in the southern channel of Fakarava Atoll, French Polynesia. We used diver observations, acoustic telemetry and biologging to show that sharks use regions of predicted updrafts and switch their core area of space use based on tidal state (incoming versus outgoing). During incoming tides, sharks form tight groups and display shuttling behaviour (moving to the front of the group and letting the current move them to the back) to maintain themselves in these potential updraft zones. During outgoing tides, group dispersion increases, swimming depths decrease and shuttling behaviours cease. These changes are likely due to shifts in the nature and location of the updraft zones, as well as turbulence during outgoing tides. Using a biomechanical model, we estimate that routine metabolic rates for sharks may be reduced by 10%-15% when in updraft zones. Grey reef sharks save energy using predicted updraft zones in channels and 'surfing the slope'. Analogous to birds using wind-driven updraft zones, negatively buoyant marine animals may use current-induced updraft zones to reduce energy expenditure. Updrafts should be incorporated into dynamic energy landscapes and may partially explain the distribution, behaviour and potentially abundance of marine predators.