Tide Gate Research Articles

The Implementation Strategy of Flood Control Program Based on Multi Criteria Assessment in Pangkalpinang City, Bangka Belitung Islands Province

Flood event is occurred almost every year in Pangkalpinang City with the most devastating flood event was occurred in 2016 historically. Irrespective of being caused by extreme rainfall and high tides, the flooding occurred due to a decrease in the hydrological condition of the watershed due to illegal tin mining activities in the upstream area. This paper discusses the flood control strategies in Pangkalpinang City which is based on Multi Criteria Assessment (MCA). The MCA considering the technical aspects (i.e. hydraulic model) and non-technical aspects (i.e. risk assessment, economic, social, and environmental aspects) to prioritize the infrastructure conbstruction. Therefore, some areas are already identified as the focal problems that need to be applied by the concept of integrated flood control program. At the moment in 2023, the first construction priority is in PDAM-Jelana Detention Pond Flow Diversion from Pedindang River in the upstream area. For the future plan, it is planned to carry out the flood control construction according to the priority analysis namely Perak Retention Pond, River Training, Rangkui Tidal Gates, Pasir Padi Sea Wall and New-Tin Detention Pond.

Modelling the compound floods upon combined rainfall and storm surge events in a low-lying coastal city

Low-lying coastal cities are highly vulnerable to compound floods, which may result from a simultaneous occurrence of storm surges and heavy rainfall. Systematic numerical analysis is essential for projecting flood scenarios upon compound events. In this study, a coupled model that integrates the 1D drainage module with the 2D overland flow module is developed and validated by taking Macau as the study area. The joint cumulative probability distribution between rainfall and storm tide are derived based on the historical typhoon data. The flood hazards are projected under designed scenarios, and an investigation is conducted on the backflow processes through drainage system and effectiveness of installing tide gates. The flood zones are delineated and the contributions of rainfall and storm tide to floods are analyzed. Storm surge exerts a greater influence on the maximum inundation depth in the western Macau Peninsula than heavy precipitation does. As the peak tidal level increases from a 10-year to a 200-year return period, the increments of flooded area ratio to the total land area are approximately 19 %. The backflows through underground drainage system could expand the tide affected area during storm events, as indicated by the backflows in the pipe 1.4 km away from the coastal boundary. By installing tide gates, backflows could be greatly eliminated in the corresponding pipes. The inundation area in the compound flood scenario is not equal to the superposition of the extents by the individual components. The transition area that is affected by both storm tide and rainfall extends from coast to inland areas under the combined effects. This study is expected to furnish valuable insights for flood risk assessment, flood hazard prevention and mitigation in low-lying coastal cities such as Macau.

Climate change impact on the compound flood risk in a coastal city

Compound flooding caused by a combination of rainfall and water level may occur in coastal cities. Under the influence of climate change, compound flooding is likely to be intensified. In this paper, using the main urban area of Haikou City as an example, we developed an event-based statistical-numerical hybrid framework to investigate the effects of sea level rise (SLR) and future rainfall changes on compound flood risk. Future rainfall was predicted by using five global climate models (GCMs) in CMIP5. A combination of GCMs and IPCC AR5 was used to predict the future SLR. The copula was then used to calculate the probabilistic risk of compound flooding (OR joint probability and failure probability) for historical and future scenarios, and the numerical model was utilized to evaluate the risk of inundation under historical and future scenarios. The probabilistic risk results show that both the probability and the failure probability of compound flooding will increase in the future. Output from GCMs indicate that when the OR event of the 5-year event (the compound flooding when at least one of the 5-year rainfall and the 5-year water level happens) occurs, the joint probability of future compound flooding will likely increase to 37.5%. The numerical model results indicate that the flood extent, flood depth and flood duration will increase under the influence of future rainfall and SLR. Under the impact of climate change, the flood depth in the FS5 case will increase by 22.85% and the flood extent in the FS5 case will increase by 41.42% compared to HS5. By controlling for variables, we also find that the combined impact of future changes in rainfall and water level on the magnitude of flooding is greater than the sum of their individual impacts. Finally, we find that water storage facilities and tide gates could be set up to mitigate compound flooding under climate change.

River- and Sex-Specific Annual Survival Rates of Mature Anadromous Alewife (Alosa pseudoharengus)

During multiple annual spawning runs from 2013 to 2021, over 9,000 mature anadromous alewife (Alosa pseudoharengus A. Wilson, 1811) were monitored with passive integrated transponders (PITs) in four rivers of the Chignecto Isthmus, Bay of Fundy, Canada. A subsample of 384 individuals tagged during 2016–2019 were aged from 3 to 6 years (mean ± SD; 4.2 ± 0.7 years, n = 232, males; 4.5 ± 0.7 years, n = 152, females). Biotelemetry revealed that one unsexed individual survived seven years post tagging, possibly making it 10–13 years old. Return rates varied among the rivers, with the lowest rates in the most anthropogenically impacted river. Biotelemetry and ageing data were used to estimate apparent annual survival rates ranging from 0.25 to 0.50 depending on the river and the year. Based on capture-mark-recapture (CMR) analysis of biotelemetry data from the three less impacted rivers, the estimated overall annual survival was 0.396, total instantaneous mortality (Z) was 0.93, and future life expectancy from time of release was 1.08 years. Frequency distribution of ages 4–6 for alewife pooled from all four study rivers estimated a lower annual survival rate of 0.301, Z = 1.20, and a future life expectancy of 0.83 years. The biotelemetry detection rates were 0.89–0.98 but varied depending on the river and the year, with the lowest rates in one river during 2017-2018 possibly related to a malfunctioning tide gate preventing upstream fish passage and subsequent detection. Based on CMR, males had a higher survival rate compared to females, which translated into an overall mean survival increase of 0.05. Alewife survivorship in our study highlighted that a limited ecosystem-based management period is required to mitigate river connectivity and mortality issues to avoid loss of population cohorts and decrease the risk of extirpation.

Impact assessment of climate change on compound flooding in a coastal city

Flood disasters in coastal cities are generally caused by the combined effect of typhoon rainfall, storm surge and other factors. Coastal cities will face more severe compound flooding under climate change. Although some studies have analyzed compound flooding under climate change, there is a lack of research considering the combined effect of sea level rise (SLR) and future rainfall changes, especially lack of the jacking effect of SLR on the volume and duration of compound flooding. This paper investigates the impact of future rainfall changes and SLR on compound flood risk, via a case study of a coastal city, Haikou, China. Future rainfall in Haikou is obtained by bias correction of rainfall from five global climate models (GCMs) in CMIP5. The SLR in 2050 and 2090 is predicted according to IPCC. Then, a 1D/2D hydrological-hydrodynamic model for dynamic simulation of surface runoff is applied to simulate compound flooding. Results show that both future rainfall changes and SLR will lead to the increase of flood extent, flood depth and flood duration. But future rainfall changes will have a greater impact on flood, and the combined effect of future rainfall changes and SLR on flood is greater than the sum of their individual effects. The individual effects of SLR and future rainfall changes would increase flood depth in 10.6 % and 32.1 % of the study area, respectively, while their combined effect would increase this proportion to 34.9 %. Also, the jacking effect of SLR on compound flooding will lead to an increase in flood volume, but it presents a nonlinear relationship that gradually slows down with the increase of SLR. A SLR of 0.3 m and 0.63 m will lead to a 2.34 % and 3.22 % increase in flood volume, respectively. And the jacking effect of SLR is more obvious when future rainfall changes are considered, which will lead to a sharp increase in the duration of compound flooding. Moreover, water storage facilities and tidal gates are effective ways to reduce the impact of climate change on compound flooding.

Nocturnal tidal barrier management improves glass eel migration in times of drought and salinization risk

AbstractAdjusted tidal barrier management (ATBM, setting tidal doors ajar during tidal rise) is currently applied in Belgium to improve glass eel passage through tidal gates. However, salt intrusion in the receiving waters due to upwelling and accumulation of saline groundwater as a result of intensive drought put severe pressure on the unrestrained use of this cost‐efficient mitigation measure. We evaluated the efficacy of a very restricted ATBM at a tidal barrier on a small canalized waterway, located 3.5 km from the sea: one out of seven gate doors was left 20 cm ajar for ca. 30 min when the water levels on both sides of the tidal barrier were approximately equal. During 20 inflow events differing in tidal flow (i.e., flood or ebb tide) and daytime (i.e., day or night) in March/April 2019, migrating glass eels were caught with a fyke net fixed on the temporally opened gate. In total, 12,853 glass eels were captured, almost all during flood tides at night (96%), with a maximum catch of 3,827 individuals per inflow event. These results show that even small windows of opportunity can help glass eels pass tidal barriers.

Impacts of environmental conditions and management of sluice gates on glass eel migration

Anthropogenic barriers such as tidal gates impair animal migration and ecological continuity. For migratory fishes, barriers may alter or impeach both upstream and downstream migrations. Juveniles of European eels, namely glass eels, have to pass those barriers when migrating upstream, whereas they have limited swimming capacities and are dependent on several environmental variables. Hydrological conditions, which can be modified by barrier management, are critical for glass eels. Here, we investigated the links between hydrological conditions and barrier management and the recruitment of glass eels at a connection between the Mediterranean Sea and a lagoon. To do that, we modeled the recruitment of glass eels over ten seasons accounting for temporal variations and co-variable effects. We modeled three aspects of recruitment: presence, level, and composition. We found that monthly and inter-annual effects explained the main part of the variations in glass eel recruitment but accounting for environmental effects improved our models, with a positive effect of temperature, for instance. We associated low levels of catches and recruitment of rather old individuals to high water flow rates when water flows out of the lagoon. Those results call for further studies on how sluice gate management may improve glass eel recruitment and seem to indicate that local stakeholders should adjust the number of open gates depending on the water level on both sides of the barrier.

Storm promotes the dissemination of antibiotic resistome in an urban lagoon through enhancing bio-interactions.

Antibiotic-resistance genes (ARGs) and resistant bacteria (ARB) are abundant in stormwater that could cause serious infections, posing a potential threat to public health. However, there is no inference about how stormwater contributes to ARG profiles as well as the dynamic interplay between ARGs and bacteria via vertical gene transfer (VGT) or horizontal gene transfer (HGT) in urban water ecosystems. In this study, the distribution of ARGs, their host communities, and the source and community assembly process of ARGs were investigated in Yundang Lagoon (China) via high-throughput quantitative PCR, 16S rRNA gene amplicon sequencing, and application of SourceTracker before, after and recovering from an extreme precipitation event (132.1mm). The abundance of ARGs and mobile genetic elements (MGEs) was the highest one day after precipitation and then decreased 2days after precipitation and so on. Based on SourceTracker and NMDS analysis, the ARG and bacterial communities in lagoon surface water from one day after precipitation were mainly contributed by the wastewater treatment plant (WWTP) influent and effluent. However, the contribution of WWTP to ARG communities was minor 11days after the precipitation, suggesting that the storm promoted the ARG levels by introducing the input of ARGs, MGEs, and ARB from point and non-point sources, such as sewer overflow and land-applied manure. Based on a novel microbial network analysis framework, the contribution of positive biological interactions between ARGs and MGEs or bacteria was the highest one day after precipitation, indicating a promoted VGT and HGT for ARG dissemination. The microbial networks deconstructed 11days after precipitation, suggesting the stormwater practices (e.g., tide gate opening, diversion channels, and pumping) alleviated the spread of ARGs. These results advanced our understanding of the distribution and transport of ARGs associated with their source in urban stormwater runoff.

Short-Term Morphological Responses of Adjacent Intertidal Flats to the Construction of Tidal Gates in an Estuarine Tributary

Tidal gates cause adverse effects on the ecological environment through the downstream acceleration of sediment deposition. This deposition process and its quantitative analysis have become a hot topic in marine science. A large-scale physical model experiment of morphological responses to the construction of a tidal gate in an estuarine tributary was performed in this study. The sediment distribution characteristics, morphologic patterns, and further analysis of the adjacent intertidal flats were investigated, triggered by the construction of tidal gates at the mouth of the Nanxi River in Zhejiang, China. The results indicated that the flood and ebb tide velocities change dramatically after the construction of the tributary tidal gates. Large amounts of sediment from the mouth of the estuary could not be entirely carried away from the flood phase to the ebb phase, resulting in downstream deposition in the vicinity of the gates. The ebb tide caused erosion of the tidal flats’ surface in the silted intertidal zone that gradually developed into a tidal channel network. The tidal channel bifurcated in the middle–upper part of the intertidal flats through continuous headward erosion, thus promoting the landward expansions of channels. Applying a set of logistic growth models to the mean sinuosity, Hausdorff dimension, and junction number data indicated that the tidal channel development progressively tended toward a state of morphodynamic equilibrium.

Opening the Door: Alosa pseudoharengus (Alewife) Passage through Tide Gates in Two Adjacent Rivers on the Chignecto Isthmus, Bay of Fundy, Canada

We assessed Alosa pseudoharengus (Alewife) upstream passage during 2016–2019 spawning runs using radio frequency identification (RFID) tracking through a periodically submerged and a constantly submerged top-hinged tide gate in the LaPlanche and Missaquash rivers, respectively, on the Chignecto Isthmus, Canada. First detection of individuals tagged in previous years (i.e., returnees) revealed synchronous upstream run timing in both rivers during 2015 and 2018. Greater delays of migrants attempting passage through the periodically submerged tide gate prompted temporary removal of 1 flapper door during 2016–2019 runs. During a 7-day period following door removal, the number of individuals passing per day increased 4- to 6-fold during 2016–2017 and less than 2-fold during 2018–2019. More than 80% of returnees passed the periodically submerged gate following door removal, decreasing mean delay to less than that of migrants attempting passage of the constantly submerged gate. Most individuals passed the periodically submerged gate during mid-flood daily tide phases and none passed during low-tide outflow due to high water velocities. Passage of the constantly submerged gate occurred during all tide phases, with 77% passing during ebb and low tides. The constantly submerged tide gate provided greater windows of opportunity, resulting in relatively shorter delays compared to the periodically submerged tide gate. Long-term monitoring in this study highlighted the effectiveness of temporary and/or adaptive mitigation when addressing issues in river connectivity and fish passage.

Lost in the North Sea-Geophysical and geoarchaeological prospection of the Rungholt medieval dyke system (North Frisia, Germany).

We performed geophysical and geoarchaeological investigations in the Wadden Sea off North Frisia (Schleswig-Holstein, Germany) to map the remains and to determine the state of preservation of the medieval settlement of Rungholt, especially its southern dyke segment, called the Niedam dyke. Based on archaeological finds and historical maps, Rungholt is assumed to be located in the wadden sea area around the island Hallig Südfall. During medieval and early modern times, extreme storm events caused major land losses, turning cultivated marshland into tidal flats. Especially the 1st Grote Mandrenke (or St. Marcellus' flood), an extreme storm surge event in 1362 AD, is addressed as the major event that flooded and destroyed most of the Rungholt cultural landscape. Cultural traces like remains of dykes, drainage ditches, tidal gates, dwelling mounds or even plough marks were randomly surveyed and mapped in the tidal flats by several authors at the beginning of the 20th century. Due to the tidal flat dynamics with frequently shifting tidal creeks and sand bars, the distribution of cultural remains visible at the surface is rapidly changing, making it hard to create a comprehensive map of the cultural landscape by surveying. Today, the Niedam dyke area is fully covered by tidal flat sediments, depriving any remains from further archaeological investigation. Since little is known about the precise location or state of preservation of these remains, our investigation aimed at the rediscovery of the medieval dyke system and associated structure with modern and accurate geophysical, geodetical and geoarchaeological methods. Magnetic gradiometry revealed a large part of the medieval dyke, confirming two tidal gates and several terps connected inland with the dyke, providing a detailed example of a Frisian medieval dyke system. Based on our results, the so far inaccurate and incomplete maps of this part of Rungholt can now be specified and completed. Beyond that, seismic reflection profiles give a first depth resolving insight in the remains of the dyke system, revealing a severe threat to the medieval remains by erosion. The site is exemplary for the entire North Frisian coast, that was influenced by multiple flood events in the middle ages to modern times.

Restoring Tidal Flow to a New England Salt Marsh

Salt marshes have experienced the brunt of human civilization for eons as they were diked for pasture or producing salt hay and less saltwater-dependent crops, filled for port, commercial, and residential development, used as landfills and to dispose of dredged material, ditched in efforts to reduce mosquito populations in coastal communities, or have had their connection to estuaries simply reduced or severed by roads and railroads. This was largely done because they were viewed as unproductive wastelands, public health hazards, or because their location was important for accessing deep water or connecting two points of land, or simply providing a desirable location for homes. In the 1960s scientists studying coastal habitats started writing about the ecological significance of these wetlands in the United States in terms the public could understand (e.g., Goodwin 1961, Odum 1961, and Teal and Teal 1969). Consequently the public was becoming more informed of the importance of these wetlands to coastal fisheries as well as to migratory birds as they witnessed accelerating destruction of salt marshes for residential and other development. In the 1960s, state legislatures began passing laws to restrict development of these wetlands, first in New England states then elsewhere (see Tiner 2013 for a comprehensive review of the history of tidal wetlands). Today salt marshes are among America’s most valued natural resources and government agencies and non-government organizations (NGOs) are both actively involved in restoring these wetlands. Most cases of this restoration involve bringing back tidal flow and more saline conditions in one way or another. Where the marshes have been crossed by a road or railroad, tidal flow has either been eliminated or restricted to varying degrees that has greatly affected soil salinities and promoted growth of brackish and freshwater species. In many cases in the northeastern U.S., these crossings have led to a drastic change in plant composition and vegetation structure – from a diverse salt marsh community dominated by low-growing halophytic plants to a virtual monoculture of common reed (Phragmites australis) – a non-native2 that favors less saline habitats and grows to 3.7 m (12 feet) or more in height under the best circumstances. Some options for restoring tidal flow in these situations include: 1) reconnecting the marsh to the adjacent estuary (where tidal flow was eliminated), 2) removing tidal gates, and 3) expanding the size of the existing culverts. These may be some of the simplest restoration projects from a construction standpoint, although concerns about increased flooding on private property surrounding the marsh is often the major hurdle to overcome. A small restoration project in Massachusetts serves as one example of the effectiveness of simply restoring tidal flow can bring about a return of salt marsh vegetation to an area that had been colonized by common reed. While some restoration projects are initiated as mitigation for destruction of wetland elsewhere, this project was a “pro-active project” – simply done for the benefit of the environment - to restore native halophytic vegetation and reduce the extent of non-native common reed.

The Economics of Storm Gates

Tidal gates have been in operation for centuries to block salt water from penetrating landscapes, while storm gates are relatively new. Storm gates block just severe storm surges while normally remaining open to allow salt water to move freely back and forth with the tides. This study evaluates the cost and flood benefits (averted flood damage) of storm gates on non-navigable coastal rivers and creeks. The study finds that only a fraction of coastal rivers should have storm gates. But selected storm gates are highly effective with long term benefits that are three times their cost. In the right place, storm gates can protect vulnerable low-lying developed areas from coastal flooding with a minimal environmental footprint.

Quantification of Biochemical Processes Governing Nitrate Delivery in a Tide Gate-Controlled Seagoing River During the Closed Tide Gate Period

Quantification of Biochemical Processes Governing Nitrate Delivery in a Tide Gate-Controlled Seagoing River During the Closed Tide Gate Period

Impact of Anthropogenic Activities and Sea Level Rise on a Lagoon System: Model and Field Observations

The long-term geomorphological evolution of a coastal lagoon is driven by hydrodynamic forcing and is influenced by climate changes and human activities. In this study, a numerical model of the Qilihai lagoon (QL) system was established based on field measurements, previous hydrology data and satellite remote sensing measurements, to simulate the geomorphological evolution of QL from 1900 to 2018. The influences of sea level rise, runoff and human activities on the evolution of geomorphology were investigated. The results of the model show that the construction projects including the tide gate, the bridge, reclamation and the straightening or widening of the tidal channel increased the net deposition within the QL system. Furthermore, the spatial distribution of tidal asymmetry during the natural time period was similar to that of the change in bed thickness. However, bed erosion or deposition was not only dependent on tidal asymmetry but it was also affected by the external sediment supply and the discharge of upstream rivers. Moreover, sea level rise had a significant effect on the tidal asymmetry; therefore, it enhanced the accumulation of sediments in the QL system, while runoff had little effect on the tidal asymmetry or geomorphological changes in the system.

Numerical simulations of compound flooding caused by storm surge and heavy rain with the presence of urban drainage system, coastal dam and tide gates: A case study of Xiangshan, China

Nowadays, most coastal cities have complex drainage systems (i.e., rivers and pipelines) connected to the sea, affecting the flooding during the co-occurrence of rain and storm surges. In this study, this compound flooding is studied by developing a coupled model based on a one-dimensional (1D) hydrological model SWMM and a two-dimensional (2D) hydrodynamic model ADCIRC. The coupling is achieved by setting the 1D model as a subroutine of the 2D model while the parallel computing scheme of the 2D model is kept using the Message Passing Interface (MPI). The coupled model is applied in Xiangshan, Zhejiang Province, along the eastern coast of China. The model accurately ensures water conservation and reproduces the observed tidal elevation, storm surge, and river water stages during Typhoons Haikui (2012) and Fitow (2013). A series of simulations are carried out to quantify the influences of coastal dams, drainage systems, control of tide gates, rain, and storm surges on the compound flooding. The results show that the drainage system enhances the connectivity between the land and the sea no matter whether the coastal dam exists, leading to faster flooding and draining. Furthermore, when a storm surge occurs, the high surge level can significantly reduce the drainage efficiency of the inland flooding during rain and thus causes more severe flooding hazards. The simulation results also suggest that urban pipelines play an important role in preventing urban flooding caused by rain. And for the prevention of storm surge inundation, an effective gate control strategy is suggested that the gates should be closed when the water levels on both sides of the dam are equal for the first time before the peak of the storm surge and are open when the water levels are equal again. Finally, the flooded area can be divided into the tidal zone, the hydrologic zone, and the transition zone to identify different flood mitigation strategies.

Storm surge induced sediment accumulation on marsh islands in the southeastern North Sea: Implications for coastal protection

Coastal marshlands in tide-dominated shallow marine systems are prone to erosion and vulnerable to long term sea level rise. The natural adaptability of such areas mainly depends on sufficient sediment supply delivered during inundation events and protection against erosion processes. Artificial structures such as dykes, revetments and tidal gates ensure protection against erosion but influence the natural adaptability of the marshland. Establishing a reasonable balance between natural adaptation processes and coastal protection measures forms a challenging task. With the use of an autonomously operating turbidity sensor network and sediment traps installed at and around a marsh island in the North Frisian Wadden Sea (Hallig Langeness, Germany), we measured suspended particulate matter (SPM) concentrations and vertical accretion adjacent to artificial revetments and breakwater constructions. Measurements included seven storm surges in the winter season 2019/20 with peak water levels of 2.94–3.65 m above sea level. We found clear relations between SPM on the tidal flats and SPM on the marshland. While SPM concentrations in the tidal flats (SPMi) during storm surges range from 0.5 ± 0.014 to 1.14 ± 0.014 g/l, those in the marshland behind breakwaters (SPMrs) only reach on average 28%–47% of SPMi depending on the specific location. SPMrs/SPMi and peak water levels shows positive correlation, while SPMrs and the duration needed to fully inundate the marshland exhibits a negative correlation. Vertical accretion of the marshland is 7.4 ± 4.6 mm for the winter season 2019/20 and therefore about 2.6 times higher than the average for four years (2016–2020) at 2.8 ± 2 mm/a. The average vertical accretion per inundation increases from 0.2 mm at moderate inundations to 0.84 mm at storm surges. The hampering effect of breakwaters on sediment accumulation seems to diminish at storm surges compared to moderate inundations.

Running on empty? Freshwater feeding by spawning anadromous alewife Alosa pseudoharengus

Anadromous alewife Alosa pseudoharengus (n=202; mean ± s.d. fork length= 231 ± 14 mm) were captured from 10 May to 27 June 2018 in an upper watershed lake on the Isthmus of Chignecto, Canada (45°57'N, 64°14'W). Thirty individuals (mean ± s.d. fork length=250 ± 12 mm) were captured in an adjacent estuary downstream of a tide gate on 25 April 2018. Comparing estuarine to freshwater specimens, mean gonad mass and gonadosomatic indices in males and females decreased approximately 40% and 60%, and 31% and 50%, respectively. Individuals were characterized as pre-spawners in the estuary and spawners in the lake. Males maintained similar body condition throughout the spawning run whereas female condition decreased 9.4% between the estuary and lake. Stomach fullness decreased comparing estuarine and freshwater specimens, yet 93% of stomachs examined from individuals captured in the lake contained prey. Most males fed throughout all spawning stages (3%-17% empty stomachs), while all females fed during pre- and post-spawning stages and some fasted during spawning (11% empty stomachs). Cumulative prey curve never reached an asymptote, either weekly or for the entire sampling period, so freshwater diet may not have been completely described. Calanoid copepods (79.3%IA ) were a diet staple, with the secondary prey of mayfly nymphs (O. Ephemeroptera) consumed more by females (13.6%IA ) than males (6.2%IA ). PERMANOVA and PERMDISP analyses revealed significant dietary differences in freshwater were weekly and not due to dispersion effects, thus most likely due to feeding on various development stages of insect species. Our results challenge the long-held paradigm that anadromous A. pseudoharengus fast during the spawning migration.

Activity Patterns of Anadromous Fish below a Tide Gate: Observations from High‐Resolution Imaging Sonar

AbstractThe construction of dams and tide gates on waterways has altered the physical structure of many coastal, estuarine, and freshwater systems. These changes have come at a cost to fish populations, most notably diadromous species, which rely on connectivity between marine and freshwater systems. These anthropogenic structures can have direct effects on migrating fish, such as blocking fish passage, or have more subtle effects, such as changing movement patterns. This study used a high‐resolution Adaptive Resolution Imaging Sonar to examine the behavior of Striped Bass Morone saxatilis, a large coastal predator, and Alewife Alosa pseudoharengus and Blueback Herring Alosa aestivalis (collectively known as river herring), which are forage fish, below a tide gate structure on the Herring River in Wellfleet, Massachusetts, during the river herring spring spawning run. Striped Bass were persistently present downstream of the tide gate and exhibited strong diurnal and tidal patterns. Activity of Striped Bass was highest at night and during ebb tides. During peak outflow periods, river herring were observed milling downstream of the dam in a scour pool, indicating delayed upstream passage. River herring upstream migration was primarily associated with daytime and during incoming tides. Downstream‐migrating river herring were primarily observed during nighttime hours. While it was documented that the tide gates provided a physical impediment to migration, their effect on predator behavior could pose an additional challenge to migrating river herring, further complicating their recovery efforts. Due to the prevalence of obstructed waterways, studying the behavior of fish around anthropogenic structures is important in understanding the full range of impacts that these systems have under varying ecological conditions and on ecological relationships.

Tide gates form physical and ecological obstacles to river herring (Alosa spp.) spawning migrations

River herring (Alosa spp.) are anadromous fish that enter North American Atlantic coastal rivers and lakes each spring to spawn. Anthropogenic structures such as dams and tide gates serve as physical obstacles that limit river herring access to spawning habitat. This study examined the physical and ecological components affecting herring passage through a tide gate by applying a time-to-event analysis framework to multiple movement behaviors derived from telemetry data. Herring had higher passage success early in the season (78%) than later (16%). Key behaviors that govern passage varied with diel period, tide, and flow direction through the gates. Furthermore, these behaviors shifted as the season progressed, consistent with the hypothesis that predator avoidance may be driving passage failure late in the spawning season.