Bathymetry Research Articles

Impact of lake expansion on the underwater topography: a case study of Lexiewudan and Yanhu Lakes on the Tibetan Plateau

ABSTRACT With increased precipitation and meltwater, most lakes on the Tibetan Plateau have expanded rapidly. However, the impact of erosion and sedimentation following lake expansion remains unclear. Using Lexiewudan and Yanhu Lakes as examples, we created a water depth inversion model using random forest method and combined it with lake bathymetric data and Landsat images and analyzed changes in underwater topography using SRTM and ICESat-2 data. The average water depths of two lakes were 5.92 and 9.82 m, and the root mean square error of inversion values were 0.85 and 0.93 m, respectively. Results showed that the underwater topography underwent considerable changes, in which at least half of the study areas experienced large topographic changes with 2–5 m. Lexiewudan Lake had a topographic change of more than 2 m in 61.28% of the total, while Yanhu Lake made up 69.78% of the total. The erosion and sedimentation volume of Lexiewudan Lake were 0.19 and 0.03 km3 and those of Yanhu Lake were 0.38 and 0.03 km3, respectively. Extensive underwater erosion and sedimentation are closely related to the original topography. Lake water movement, sediment transport, and permafrost degradation in flooded areas may also affect changes in underwater topography.

Using Machine Learning Techniques to Predict Significant Wave Height Compared with Parametric Methods

Prediction of Sea Wave parameters is an important issue as it is the main design factor for maritime structures. Previously, researchers have used many parametric and numerical approaches, which may be complex in application, take a long time in preparation and sometimes require a bathymetric survey. Recently, soft computing techniques such as Fuzzy Inference Systems, Genetic Algorithm, Machine Learning, etc. have been used to predict sea wave parameters in many marine areas around the world. The ease of application, high accuracy and low computational time of these techniques make them a very good choice in many engineering applications. This study focuses on prediction of significant wave height (Hs) by applying one of the most advanced Machine Learning techniques known as Support Vector Machine (SVM). SVM models are built on the basis of different Kernel functions (Linear, Sigmoid, Radial Basis Function, and Polynomial) which transform the input data into an n-dimensional space where a hyperplane can be generated to partition the data. The results of SVM models are analyzed, evaluated and then compared with the results of commonly used parametric models (P-M, SPM, and CEM). This study shows that the P-M model has reliable and satisfactory results among all parametric models, as its statistical errors are close to those of SVM models (RBF and Polynomial), while all of them are identical in their correlation factors (0.999). Moreover, the parametric models (SPM and CEM) are more accurate in their results than the SVM models (Linear and Sigmoid). Also, this study confirms that the SVM models (RBF and polynomial) are the most accurate models overall, as they have the best generalization error among all models. Finally, it can be concluded that SVM models (RBF and Polynomial) are a promising technique in the sea wave height prediction and can be used as an economic and accurate alternative solution to other prediction models.

Facies variations in gravelly cyclic steps deposited from turbidity currents: Miocene fan delta front deposits compared with a modern active fan delta, central Japan

AbstractGravelly cyclic steps formed by turbidity currents have recently been widely recognised in the geological record. However, the comparison between modern and ancient gravelly cyclic steps remains challenging. In this study, the facies variations of gravelly cyclic steps deposited from turbidity currents in an outcrop of Miocene fan delta front deposits in central Japan are compared with the geomorphic evolution of analogous cyclic steps on the active fan delta front in modern geological systems. These cyclic steps share common characteristics in setting, grain size and dimensions, allowing direct comparison between ancient and modern examples. Repeat bathymetric surveys of the modern Kurobe River fan delta have revealed various types of upslope migrating bedforms interpreted as cyclic steps. Most of these are short‐lived due to erosion of thalwegs by powerful surge‐type turbidity currents triggered by slope failures or burial of thalwegs by deposition, possibly from river‐fed hyperpycnal flows. Such erosion and burial events occur annually on the fan delta front, resulting in compensational cycles. Sedimentary facies of the Miocene fan delta front deposits include conglomerate with a gently upslope dipping erosional base, backset‐stratified sandstone and foreset‐stratified sandstone, which are interpreted as deposits of hydraulic jumps in high‐density turbidity currents in scours on the stoss sides of cyclic steps. Parallel‐stratified conglomerate sandstone is an additional component. Although previous facies models of gravelly cyclic steps have focussed on deposits on stoss sides, a comparison of modern and ancient examples suggests that facies on the lee sides could be parallel‐stratified conglomerate sandstone and undulating bedforms, reflecting supercritical flow conditions. The present study also suggests that hyperpycnal and surge‐type high‐density turbidity currents may deposit different types of facies and play different roles in the construction and destruction of cyclic steps. The present study has significant implications for facies models of gravelly cyclic steps.

Palaeodrainages of the Sunda Shelf detailed in new maps

The Sunda Shelf is a prime biodiversity hotspot where some of the planet's most endemic species can be found. Much of the diversity in this important bioregion has been shaped by sea-level fluctuations that took place during the Pleistocene. Using depth contours obtained from the General Bathymetric Chart of the Oceans Grid 2023, we provide high-resolution reconstruction of land areas and palaeo-drainages on the Sunda Shelf at the 50, 75, 100, and 120 m isobaths, as well as palaeo-catchments at the 120 m isobath, in order to elucidate the history of this region. The maps presented here aim to reconstruct the connection between palaeo-rivers in the Sunda Shelf and contemporary rivers and identify possible dispersal routes and barriers for the floras and faunas/biotas associated with riverine systems found here.

Exploring soil erosion and reservoir sedimentation through the RUSLE model and bathymetric survey

The aim of the paper was to compare the soil erosion in a river catchment with the sediment volume accumulated at the river mouth. Firstly, the sediment yield was estimated in GIS based on the soil loss according to the RUSLE model, and then further integrated into the sediment production equation. Following this, we estimated the sediment volume accumulated at the river mouth based on the diachronic overlap of topographic and bathymetric data. This methodology was validated for the Eselnita catchment exiting into the Iron Gates I Reservoir. The LS factor has an average value of 4, with lower values for the forest cover. The C factor has an average value of 0.057 being statistically correlated with the RUSLE result. The average soil loss was estimated at approximately 1.89 t ha-1 yr -1, a value that is validated by previous studies as a low risk of erosion at national scale. The sediment transfer model indicates a distribution of cells sediment production strongly correlated with the time travel to the discharge channels. Overall, the sediment volume obtained by using the RUSLE model corresponds to about 70% of the sediment volume accumulated at the river mouth during 53 years (1970-2022). The difference in sedimentation may be due to human activities along the river mouth’s banks to extend the built-up area and to enjoy the waterscape. This paper is relevant for the topic of reservoir sedimentation and recommends the use of the RUSLE model to predict the sediment contribution, especially for small ungauged catchments.

The Sofu Seamount Submarine Volcano Present in the Source Area of the October 2023 Earthquakes and Tsunamis in Japan

AbstractOn 8 October 2023 (UTC), unique earthquakes occurred in the Izu‐Ogasawara Arc, Japan, in which the P‐ and S‐phases were barely visible and only the T‐phases were evident, followed by tsunamis that reached islands in the Izu‐Ogasawara Arc and a wide area of the Pacific coast of southwest Japan. Our estimated T‐phase source area coincides with the Sofu Seamount, which was previously unrecognized as an active submarine volcano. A bathymetric survey of the seamount conducted 1 month after the event revealed characteristics of the seamount with a caldera and a central cone. Compared to the bathymetry in 1987, the topography in the caldera had changed significantly such as a crater forming in the central cone. This seamount is likely to be an active volcano. The topographic changes on the caldera‐sized scale that occurred at the caldera can be explained as a source of the October tsunami.

Bathymetric analysis using multifrequency multibeam echosounder

Making a nautical chart for safe navigation is a bathymetric survey’s primary goal. Multifrequency MBES have been developed over the last few decades, and their introduction has dramatically improved the efficiency, accuracy, and spatial resolution of coastal and ocean mapping. The goal of multifrequency MBES is to increase the subsurface’s detection resolution. To obtain an accurate picture of the seabed, the user can lessen the impact of this subsidence by running surveys in three different modes at once. With the help of multifrequency MBES, this study will analyze bathymetry in shallow coastal waters. The digital bathymetric model’s (DBM) frequencies are remarkably close. The depth value of the study site ranges from –20 m to–70 m with reference to lowest water surface (LWS) based on the produced DBM. Generally, the difference between 100 kHz, 200 kHz, and 400 kHz is as small as 0–30 cm, and a small part is 30–60 cm. The volume between frequencies for an area of 1 ha is between 90 m3 to 440 m3. If the thickness of the dredged sediment is 1 m, then the difference in volume between frequencies is less than 5%. The bathymetry difference between 100 kHz and 400 kHz frequencies to –10 cm is dominated by the region of 0 cm. Dredging volume inter frequency ranges from 0.042 m3/m2 to 0.068 m3/m2.

Robust algorithm for automatic surface-based outlier detection in MBES point clouds

Bathymetric multibeam echosounder systems (MBES) provide high-resolution mapping of underwater topography but are highly susceptible to errors due to harsh environmental conditions and the measurement process. Traditionally, manual post-processing is required to ensure data quality, a time-consuming, expensive, and subjective task. To address this issue, we propose a surface-based algorithm for pre-processing and cleaning MBES data that reduces manual intervention and improves consistency. A surface-based algorithm models the underwater topography as a surface instead of processing individual points. By assuming a continuous surface for underwater geometry, the algorithm easily identifies observations that deviate significantly from this model. The method combines a hierarchical B-spline surface with iterative robust estimation to automate data cleaning. Preliminary results on example datasets show a balanced outlier detection accuracy of 0.99, with manual processing time reduced from 2 days to just 30 min.

Storm-Driven Tree Exposure and Geomorphic Change: Predicting the Distribution of Preserved Late Pleistocene Tree Stumps on the Outer Alabama Continental Shelf

The Alabama Underwater or Drowned Forest is a well-preserved Late Pleistocene (dated to 72–56 ± 8 ka, 2σ) terrestrial landform on the northern Gulf of Mexico continental shelf that provides geomorphic and ecosystem information rarely preserved during the glacial intervals. Stumps of bald cypress (Taxodium distichum (L.) Rich.) trees were exposed in ∼18 m of water following Hurricane Ivan in 2004. This research investigates geomorphic changes to the Mississippi-Alabama-Florida (MAFLA) sand sheet, which presents as shore-oblique Holocene sand ridges, and the exposure and burial of tree stumps following the passage of Hurricane Sally in 2020 using repeat sidescan and bathymetric surveys (2015–2016 and 2021). Using two newly identified tree exposure areas and their geological properties, this research also hypothesized a new location where tree stumps may be outcropping. The bathymetry indicates regions with up to ∼1 m of erosion and deposition over the five years between the two surveys. Similarly, the sidescan sonar indicates changes in the location and numbers of exposed tree stumps as well as between 47,000 and 62,500 tons of sediment erosion within the study area following Hurricane Sally. The 2015 and 2016 data found 25 tree contacts whereas the 2021 survey found 76 tree contacts and only 5 of them occurred in both surveys suggesting the tree exposures are dynamic and presumably changing with the passing of large tropical cyclones. Additionally, the hypothesized exposure location had 26 newly identified tree stump contacts within a mixed texture unit along the sand-mud boundary, confirming our understanding of the geomorphic characteristics leading to the exposure of the buried forest. This research will expand the potential areas for investigations into Late Pleistocene ecosystems and landforms and their associated climatic and ecologic conditions in the Gulf of Mexico as well as in other passive continental margins.

A dual-stage coverage path planning method for bathymetric survey using an AUV in graph-based SLAM framework considering positioning uncertainty

Autonomous underwater vehicles (AUVs) are becoming increasingly popular for seabed coverage survey tasks but suffer from a serious problem of positioning error accumulation, which leads to low path tracking accuracy and a low coverage rate of the target area. A dual-stage AUV path planning (DSPP) approach was proposed within a simultaneous localization and mapping (SLAM) framework for coverage bathymetric surveys. In the first stage, a global coverage path is designed in a lawnmower style. Crossed paths are added to generate periodic loop closures in SLAM, which can improve the efficiency of online replanning. In the second stage, with a probabilistic neural network (PNN) used for feature-rich bathymetric sub-map identification, an entropy-based online path replanning approach was implemented using 20 templates to adjust the global path to produce accurate loop closures for positioning error correction. Two bathymetric datasets were used to test the proposed DSPP method using a self-developed experimental simulation system. Experiments verified that DSPP can significantly improve the positioning accuracy and coverage rate with acceptably longer paths. In a 6000 m× 5000 marea,the DSPP approach reduced the positioning error by 76% compared with the pure dead reckoning method, and the coverage ratio reached 98.15%.

Joint-optimized coverage path planning framework for USV-assisted offshore bathymetric mapping: From theory to practice

Designing effective coverage routes for unmanned surface vehicles (USVs) is crucial to improve the efficiency of offshore bathymetric surveys. However, existing coverage planning methods for practical use are limited, primarily due to the large-scale surveying areas and intricate region geometries caused by coastal features. This study aims to address these challenges by introducing a coverage path planning framework for USV-assisted bathymetric mapping, specifically aimed at the joint optimization of paths to cover numerous complex regions. Initially, we conceptualize the large-scale bathymetric survey mission as an integer programming model. The model uses four distinct decision variables to meticulously formulate length calculations, inter-regional connections, entry and exit point selections, and line sweep direction. Then, a novel hierarchical algorithm is devised to solve the problem. The method first incorporates a bisection-based convex decomposition method to achieve optimal partitioning of complex regions. Additionally, a hierarchical heuristic optimization algorithm that seamlessly integrates the optimization of all influencing factors is designed, which includes order generation, candidate pattern finding, tour finding, and final optimization. The reliability of the framework is validated through semi-physical simulations and lake trials using a real USV. Through comparative studies, our model demonstrates clear advantages in computational efficiency and optimization capability compared to state-of-the-arts, with its superiority becoming more pronounced as the problem scale increases. The results from lake trials further affirm the efficient and reliable performance of our model in practical bathymetric survey tasks.

Reconciling short- and long-term measurements of coastal cliff erosion rates

Oblique terrestrial laser scanning (TLS) enables topographic change detection at scales (10−1 –100 cm) that are appropriate for coastal cliff erosion monitoring. Despite this, published applications of TLS on cliff are limited to a small number of sites around the world. Here we report new TLS point cloud datasets from 9 years of monitoring (2014–2023) at Rothesay Bay within the Hauraki Gulf, New Zealand, which has relatively low wave energy and a meso-tidal range. The 120 m-length scan area includes cliffs of 10–30 m height, formed of horizontally bedded soft sedimentary flysch rock. The cliffs are fronted by an 140 m wide near-horizontal shore platform that terminates in an abrupt seaward edge. Previous research at this site has estimated long-term cliff erosion rates within a range of 1.4 ± 0.1 to 14.3 ± 0.1 mm/year on the basis of measured shore platform width, assuming that the shore platform has widened over time over 6000 years of stable Holocene sea level, and that the seaward edge of the shore platform has not retreated. Volumetric cliff-face erosion rates were detected through 17 scans over a 9-year window (2014–2023), including intensive monthly TLS scanning between July 2021 and July 2022. Results show that the average cliff recession rate over the past decade has been 41 ± 2 mm/year, and monthly scans show a range in erosion rates of 30 to 288 mm/year. The cliff recession rate detected with TLS is 3 to 30 times higher than erosion rates derived based on the shore platform width. If erosion had been constant at this rate over approximately 6000 years, a total cliff retreat of >245 m would be expected, whereas the contemporary shore platform is only 140 m wide. We discuss two possible hypotheses for the confounding width of the modern shore platform: 1) that modern cliff retreat rates are faster than past erosion rates; 2) that the seaward edge of the shore platform does not reliably demarcate Holocene cliff recession. We present new bathymetric survey mapping seaward of the shore platform edge that reveals multiple rocky features that are distinguished by steep slope breaks and planar surfaces. Understanding the evolution of the intertidal shore platforms during the Holocene era may necessitate new insights on how cliffs formed toward the end of the last marine transgression. This could potentially be investigated through the study of subtidal marine bathymetry.

Deteriorating wintertime habitat conditions for waterfowls in Caizi Lake, China: Drivers and adaptive measures

China has made enormous strides to achieve high-quality development and biodiversity conservation, and the establishment of nature-protected areas is one of the essential initiatives. Caizi Lake involves a natural reserve and two national wetland parks, accommodating winter migratory waterfowl over the middle and lower Yangtze River basin in China. However, the water transfer from the Yangtze River to the Huai River (YR-HR water transfer) has modified the winter hydrological conditions of Caizi Lake, negatively affecting wintertime waterfowl habitats. Hence, conserving wintertime waterfowl habitats necessitates knowledge of the dynamical mechanisms behind the impacts of YR-HR water transfer on wintertime waterfowl habitats and adaptive measures. Here we developed a machine learning model, the normalized difference vegetation index, and on-spot observatory datasets such as the spatial distribution of waterfowl species and underwater topography of Caizi Lake. We found that the rising winter water level of Caizi Lake encroaches on winter waterfowl habitat with extremely high suitability. Meanwhile, rising water levels reduced waterfowl food sources. Thus, rising water levels due to YR-HR water transfer deteriorated waterfowl living conditions over Caizi Lake. Therefore, we proposed adaptive measures to alleviate these negative effects, such as water level regulation, artificial feeding of waterfowls, restoration and reconstruction of contiguous mudflats, grass flats. This study highlights human interferences with waterfowl habitats, necessitating biodiversity conservation at regional scales.

Sedimentological, Geochemical, and Environmental Assessment in an Eastern Mediterranean, Stressed Coastal Setting: The Gialova Lagoon, SW Peloponnese, Greece

This study describes the prevalent sedimentological and geochemical patterns and investigates the environmental status of the bottom of Gialova lagoon, a highly vulnerable coastal site of the EU’s Natura 2000 network. For this task, lithological, geochemical, and microfaunal analyses of sediment samples were combined with a high-resolution bathymetric survey. Potential pollution was determined using geochemical-based (EF, I-geo, and PLI) and faunal (Foram-AMBI) indices. We find that sedimentation is mainly controlled by the bottom morphology, hydrodynamic variations, and biogenic productivity of the lagoon. The application of the multivariate factor analysis technique revealed four dominant factors explaining the geochemical processes occurring in the lagoon. The first factor, namely “terrigenous aluminosilicates associated with Corg vs. autochthonous biogenic carbonates”, discriminates the deposition of detrital sediments, related to the high adsorption of heavy metals—versus bioclastic sediments. The “sulfides” factor represents an anoxic phase of the lagoon floor, whereas the “Mn-oxyhydroxides” factor indicates increased manganese content with several compounded trace elements. The “phosphate” factor reveals multiple sources of phosphorus in the lagoon. The lagoon bottom shows negligible to minor contamination in heavy metals, except Mo and Pb, which induce moderate pollution levels. The maximum contamination and environmental stress concern two small-sized, shallow basins within the lagoon.

Research on the design of multibeam bathymetric survey line based on geometric derivation

Research on the design of multibeam bathymetric survey line based on geometric derivation

Evolution, sedimentation and thermal state of the emerging pro‐glacial lakes at Witenwasserengletscher, Switzerland

AbstractAs glaciers retreat worldwide, local basal depressions are exposed where new pro‐glacial lakes are forming. Although the formation of such new lakes has been mapped widely, the impact of their interaction with the glacier on sediment dynamics and the thermal state is rarely studied. At the example of Witenwasserengletscher, Switzerland, we use historic aerial imagery and a bathymetric survey to investigate in detail the interaction of glacier retreat, lake formation and sedimentation. Three lakes have emerged since the mid‐1990s with mean depths between 1.25 and 6 m. The deepest lake lost contact to the ice in 2009 with a delta forming from mobilized sub‐glacial sediment. Phases of direct contact of the glacier with the lakes are found to increase terminus retreat and affect the thermal state and sedimentation. In summer, lake water temperatures in these small ice‐contact lakes stay close to 0°C, whereas the disconnected eastern lake shows temperatures consistently over 6°C. Temperature profiles from 2021 show that after losing ice contact, warm sediment‐rich glacial water forms an underflow that is breaking through the summertime stratification with warm water over cold water. In this case, density stratification is dominated by suspended sediment rather than temperature. Sedimentation shows a high multiannual variability and is dependent on a multitude of factors, ultimately on the routing of glacial streams. These tend to migrate towards the centre of the valley as the glacier retreats. Our study shows that during deglaciation lake evolution, sediment redistribution and the thermal state are highly dynamic and pro‐glacial lakes strongly affect the sediment evolution and may thereby impact on the ecosystem in pro‐glacial streams.

Research on multi-beam survey line system based on dynamic programming algorithm

This paper establishes a calculation model for the coverage width and overlap rate of a multi-beam survey line system [1], and optimizes the multi-beam bathymetric survey plan for marine areas. Through the dynamic programming algorithm, a reasonable survey line plan is designed based on the actual marine area depth. The research content includes: Model Establishment: Construct a calculation model for coverage width and overlap rate, determining the coverage width and overlap rate at each position. Three-Dimensional Space Model: Using the survey vessel as the origin and combining marine area information, solve for the coverage width at different angles. Shortest Survey Line Plan: Using the dynamic programming algorithm, determine the shortest survey line plan, with the dynamic transfer equation determined by the overlap rate index. The total length of the survey line in this plan is calculated to be 114,824 meters. Specific Survey Line Plan Design: Using sea depth data and cubic spline interpolation to complete the discrete point plane, construct approximate width and slope. Under the condition of relaxing the overlap rate to 5%-30%, the shortest survey line length is obtained as 398,059 meters, with a missing survey area ratio of 0%, and the total length of parts with an overlap rate exceeding 20% is 25,759 meters, accounting for 6.4%. This study provides theoretical basis and calculation methods for optimizing multi-beam bathymetric survey plans.

Authentic fault models and dispersive tsunami simulations for outer-rise normal earthquakes in the southern Kuril Trench

The southern Kuril Trench is one of the most seismically active regions in the world. In this study, marine surveys and observations were performed to construct fault models for possible outer-rise earthquakes. Seismic and seafloor bathymetric surveys indicated that the dip angle of the outer-rise fault was approximately 50°–80°, with a strike that was slightly oblique to the axis of the Kuril Trench. The maximum fault length was estimated to be ~ 260 km. Based on these findings, we proposed 17 fault models, with moment magnitudes ranging from 7.2 to 8.4. To numerically simulate tsunami, we solved two-dimensional dispersive wave and three-dimensional Euler equations using the outer-rise fault models. The results of both simulations yielded identical predictions for tsunami with short-wavelength components, resulting in significant dispersive deformations in the open ocean. We also found that tsunami generated by outer-rise earthquakes were affected by refraction and diffraction because of the source location beyond the trench axis. These findings can improve future predictions of tsunami hazards.Graphical

Time-lapse surveys reveal patterns and processes of erosion by exceptionally powerful turbidity currents that flush submarine canyons: A case study of the Congo Canyon

The largest canyons on Earth occur on the seafloor, and seabed sediment flows called turbidity currents play a key role in carving these submarine canyons. However, the processes by which turbidity currents erode submarine canyons are very poorly documented and understood. Here we analyse the first detailed time-lapse bathymetric surveys of a large submarine canyon, and its continuation as a less-deeply incised channel. These are also the most comprehensive time-lapse surveys before and after a major canyon-channel flushing turbidity current. These unique field data come from the Congo Submarine Fan offshore West Africa, where canyon flushing turbidity currents between 2019 and 2020 eroded ~2.65 km3 of seabed sediment, as they travelled for over 1100 km at speeds of 5–8 m/s. This eroded sediment volume is equivalent to ~19–33 % of global sediment flux from all rivers to the oceans. The time-lapse surveys cover 40 % of the 1100 km long submarine canyon-channel. They show that erosion was predominantly (94 %) along the canyon-channel axis, with only 6 % from failures along canyon or channel flanks. However, erosion along the canyon-channel floor was very patchy; some areas were eroded to depths of 10–20 m, whilst intervening areas showed no significant change. Knickpoints with up-slope migrating headscarps account for 22 % of the total eroded volume. One knickpoint in the deep-sea channel migrated by 21 km in one year, making it the fastest moving submarine knickpoint yet documented. Most (62 %) eroded sediment was in zones extending across the canyon or channel floor, without distinct headscarps as is the case for knickpoints. Erosion restricted to outer bends only comprised 10 % of the total, suggesting processes of erosion differ significantly from meandering rivers in which outer bend erosion is more important. Patchy seabed erosion appears to be mainly due to flow-bed processes (e.g. knickpoints), but spatial variations in seabed sediment properties may also play a role. The irregular seabed erosion occurs despite near-uniform flow speeds observed between moorings and submarine cable breaks with spacing of tens to hundreds of kilometers. Patchy and localised erosion has important implications for assessing hazards to seabed telecommunication cables, which are more likely to break in areas of deep erosion, and for creating appropriate numerical models of seabed erosion and turbidity current behaviour, or how to interpretate ancient submarine canyons and channels in rock outcrops.

Anthropogenic and environmental drivers of Acanthurus achilles presence in Hawai‘i

Despite the ecological and social importance of reef fishes, data on their populations, habitat use, and other drivers are often scarce, which creates challenges for effective management. These challenges are particularly acute for rare or at-risk species such as Acanthurus achilles, a reef fish with a documented population decline in recent years in Hawai‘i, USA. We used a data set of in situ fish surveys from across the main Hawaiian Islands combined from multiple survey programs to quantify A. achilles presence and absence and applied generalized linear mixed-effects models to examine the relationships between presence of (1) all individuals, (2) juveniles, and (3) adults with 27 spatially continuous environmental and anthropogenic drivers to understand the main drivers of presence. Using the modeled relationships between presence and all drivers, we predicted the probability of A. achilles presence at a 100 m scale within the 30 m depth contour of the main Hawaiian Islands. Environmental drivers, especially habitat drivers such as depth and rugosity, emerged as significant drivers of A. achilles presence, while anthropogenic drivers like land-based pollution and fishing had fewer significant relationships with A. achilles presence. The predicted probability of presence varied both between islands as well as within islands, with the highest probability of presence around Kaho‘olawe and Hawai‘i and the lowest around O‘ahu. Our modeling approach and high-resolution spatial predictions provide empirical evidence of the importance of environmental drivers in explaining A. achilles presence and identify preferred habitat at relevant scales for fisheries management.