The use of singlebeam echo-sounder depth data to produce demersal fish distribution models that are comparable to models produced using multibeam echo-sounder depth

Seafloor characteristics can help in the prediction of fish distribution, which is required for fisheries and conservation management. Despite this, only 5%–10% of the world's seafloor has been mapped at high resolution, as it is a time-consuming and expensive process. Multibeam echo-sounders (MBES) can produce high-resolution bathymetry and a broad swath coverage of the seafloor, but require greater financial and technical resources for operation and data analysis than singlebeam echo-sounders (SBES). In contrast, SBES provide comparatively limited spatial coverage, as only a single measurement is made from directly under the vessel. Thus, producing a continuous map requires interpolation to fill gaps between transects. This study assesses the performance of demersal fish species distribution models by comparing those derived from interpolated SBES data with full-coverage MBES distribution models. A Random Forest classifier was used to model the distribution of Abalistes stellatus, Gymnocranius grandoculis, Lagocephalus sceleratus, Loxodon macrorhinus, Pristipomoides multidens, and Pristipomoides typus, with depth and depth derivatives (slope, aspect, standard deviation of depth, terrain ruggedness index, mean curvature, and topographic position index) as explanatory variables. The results indicated that distribution models for A. stellatus, G. grandoculis, L. sceleratus, and L. macrorhinus performed poorly for MBES and SBES data with area under the receiver operator curves (AUC) below 0.7. Consequently, the distribution of these species could not be predicted by seafloor characteristics produced from either echo-sounder type. Distribution models for P. multidens and P. typus performed well for MBES and the SBES data with an AUC above 0.8. Depth was the most important variable explaining the distribution of P. multidens and P. typus in both MBES and SBES models. While further research is needed, this study shows that in resource-limited scenarios, SBES can produce comparable results to MBES for use in demersal fish management and conservation

The use of singlebeam echo-sounder depth data to produce demersal fish distribution models that are comparable to models produced using multibeam echo-sounder depth

Seafloor characteristics can help in the prediction of fish distribution, which is required for fisheries and conservation management. Despite this, only 5%–10% of the world\u27s seafloor has been mapped at high resolution, as it is a time-consuming and expensive process. Multibeam echo-sounders (MBES) can produce high-resolution bathymetry and a broad swath coverage of the seafloor, but require greater financial and technical resources for operation and data analysis than singlebeam echo-sounders (SBES). In contrast, SBES provide comparatively limited spatial coverage, as only a single measurement is made from directly under the vessel. Thus, producing a continuous map requires interpolation to fill gaps between transects. This study assesses the performance of demersal fish species distribution models by comparing those derived from interpolated SBES data with full-coverage MBES distribution models. A Random Forest classifier was used to model the distribution of Abalistes stellatus, Gymnocranius grandoculis, Lagocephalus sceleratus, Loxodon macrorhinus, Pristipomoides multidens, and Pristipomoides typus, with depth and depth derivatives (slope, aspect, standard deviation of depth, terrain ruggedness index, mean curvature, and topographic position index) as explanatory variables. The results indicated that distribution models for A. stellatus, G. grandoculis, L. sceleratus, and L. macrorhinus performed poorly for MBES and SBES data with area under the receiver operator curves (AUC) below 0.7. Consequently, the distribution of these species could not be predicted by seafloor characteristics produced from either echo-sounder type. Distribution models for P. multidens and P. typus performed well for MBES and the SBES data with an AUC above 0.8. Depth was the most important variable explaining the distribution of P. multidens and P. typus in both MBES and SBES models. While further research is needed, this study shows that in resource-limited scenarios, SBES can produce comparable results to MBES for use in demersal fish management and conservation

Determining the COB location along the Iberian margin and Galicia Bank from gravity anomaly inversion, residual depth anomaly and subsidence analysis

International audienc

Morphology and sand characteristics at five recreational beaches in Pahang

Pahang coastline stretched approximately 209 km long in the east coast Peninsular Malaysia and blessed with varying width. The coastal zone provides many recreational beaches, attracting an estimated of 600 thousand visitors per annum. These beaches had become familiar attraction for tourism and recreational activities. Despite that, tourism activities shed positive economic value to the locale, the ecological status of the recreational beaches are now in alarm. The attraction along the coastal zone will be negatively influenced should the beaches are harmed due to the ongoing anthropogenic activities. Following a preliminary visual survey of approximately 20 beaches located in the three regions alongside the coastline, namely north (Kuantan), middle (Pekan) and south (Rompin), 5 sites were selected for the study site. Beach profiles, sediment samples, and tide characteristics were collected at each site in two different periods; late northeast monsoon and inter-monsoon. The beach morphology analysis found that, the beach tends to be narrower in the centre and gradually becomes wider in the northern and southern stretches. The changes in width suggest that the effect of headland and pocket beach characteristics on the hydrodynamic movement and sediment transport activities. The variations of beach’s slopes were also observed to be from a few degrees up to more than 45 degrees. Analysis of sediment grain size distribution was performed using GRADISTAT. The sediment samples were classified according to their mean, sorting, skewness and kurtosis values. Results indicated that most sites are classified as medium sand, poorly sorted, hold a negative skewness and dominated by mesokurtic and leptokurtic. Finally, results are compared to previous works done along Pahang coastline to validate the significant contributing factors that affect the sediment characteristics and beach width

Sustainability of wave energy resources in southern Caspian Sea

This study aims to evaluate the wave energy potential and its spatial and temporal variations in the southern Caspian Sea. For this purpose, SWAN model was used to hindcast wave characteristics for 11 years. The wave energy assessment was conducted in four nearshore stations in order to assess the feasibility of wave energy harvesting and locate the most appropriate station. Assessment of seasonal and monthly variations of the mean and maximum wave powers showed that the central station contains the highest values, especially in November; while the north-eastern station has the lowest values with the highest variation of directional distribution of the wave power. Moreover, the seasonal and monthly variability indices indicate a relatively stable wave condition in all stations. The total and exploitable storages of wave energy were also higher in the central station. Therefore, it was concluded that the central station is the most appropriate location for wave energy harvesting. Furthermore, the inter-annual variations of the mean wave power illustrate no significant long-term change in wave power in the southern Caspian Sea. Therefore, considering the relatively stable condition and comparable exploitable storage of wave energy, this area can be a suitable location for developers

Mapping shallow water habitats of the Wallabi Group, Houtman Abrolhos Islands, using remote sensing techniques

The use of mapping techniques to identify and quantify habitats is becoming an increasingly important tool for the effective management of marine resources. With a multitude of techniques such as remote sensing, acoustic surveys and towed video all commonly used, the decision on the methodology to use depends on the resolution of output data required to answer the objectives of the survey, the spatial extent and location of survey site as well as the associated costs of surveyin

Preeruptive flow focussing in dikes feeding historical pillow ridges on the Juan de Fuca and Gorda Ridges

Linear, hummocky pillow mound volcanism dominates at slow and intermediate spreading rate mid-ocean ridges. Volcanic hummocks are thought to be formed by low effusion rates or as a result of flow focussing during effusive fissure style eruptions in which the initial dike intercepts the seafloor and erupts along its entire length. In this study, high-resolution autonomous underwater vehicle (AUV) bathymetry is used to accurately map the extents of four historical fissure eruptions of the Juan de Fuca and Gorda ridges: on the North Gorda, North Cleft, and CoAxial ridge segments. The four mapped eruptions take the form of pillow mounds, which are similar in both lithology and dimension to hummocks on the Mid-Atlantic Ridge. Pillow mounds may be isolated, or coalesce to form composite mounds, aligned as ridges or as clustered groups. In three of the four mapped sites, the eruptions were discontinuous along their lengths, with pillow mounds and composite mounds commonly separated by areas of older seafloor. This style of discontinuous eruption is inconsistent with typical en echelon fissure eruptions and is probably due to a mildly overpressured, fingering dike intersecting the seafloor along parts of its length

Controls on the 129I/I ratio of deep-seated marine interstitial fluids: 'Old' organic versus fissiogenic 129-iodine

Iodine and its radioisotope 129I have been successfully used to trace the origin of pore waters in submarine fluid escape structures because of their close association with organic material in deeply buried sediments. We report here halogen concentrations and 129I/I ratios for fluids of five mud volcanoes sampled along an E–W transect across the Gulf of Cadiz in the NE Atlantic Ocean. Concentrations of iodide and bromide increase consistently seaward accompanied by a decrease in 129I/I ratios from 6490 × 10− 15 to 663 × 10− 15. The exceptionally high 129I/I ratios at the near-shore locations reflect the presence of fissiogenic 129I, produced in situ by spontaneous fission of 238U within terrigenous sediments and released into pore water during clay mineral diagenetic processes. The observed 129I/I and halogen trends, together with similar changes in 87Sr/86Sr ratios, indicate a progressive seaward transition from inorganic-terrigenous to organic-marine fluid sources. Comparison of our results with literature data for varying geological settings reveals a general relationship between fissiogenic 129I, radiogenic 87Sr and the lithology or provenance of rocks and sediments, respectively. While 129I/I ratios in continental rock-hosted aquifers and terrigenous sedimentary systems are dominated by in situ production of fissiogenic 129I, iodine isotopes in oceanic settings or volcanogenic marine sediments reflect the release of ‘old’ iodine from deeply buried organic matter. The Gulf of Cadiz represents the full transition between these continental and oceanic 129I/I and 87Sr/86Sr end members. This is the first systematic investigation of fissiogenic 129I production in marine sedimentary environments

Interpreting the dynamics of submarine landslides through hydroacoustic modeling, West Mata volcano, NE Lau Basin

Landslides are an integral process in the development of submarine volcanoes, but these events are rarely recorded and observed. Therefore, understanding how the morphology of volcanoes evolve requires information on landslides. Hydroacoustic signals were analyzed for the purposes of characterizing frequent landslides on West Mata volcano during a 5-month eruptive period. Over 200 landslide signals have been compared in conjunction with hydroacoustic modeling to better understand the dynamics that control them. We used interference patterns produced by multipath rays to identify and model these slope failures. Landslides were most clearly captured on the north and west stations, suggesting a source on the western face of West Mata. This is consistent with a zone of high sediment accumulation previously found by bathymetric depth difference mapping. Landslides were found to initiate ~200-300 m below the summit and travel at speeds of 4-8 m/s, and possibly up to 20 m/s. Slope failures were observed during periods of high eruptive activity suggesting failure by unstable tephra loading preferentially at sites of previous sliding. Landslides at West Mata also tend to occur in clusters with decreasing run out distances over time. It is recommended that future studies involve a denser hydrophone network to better locate landslides and model slide mechanics