Multibeam echosounders are widely used for 3D bathymetric mapping, and increasingly for water column studies. However, they rapidly collect huge volumes of data, which poses a challenge for water ...column data processing that is often still manual and time-consuming, or affected by low efficiency and high false detection rates if automated. This research describes a comprehensive and reproducible workflow that improves efficiency and reliability of target detection and classification, by calculating metrics for target cross-sections using a commercial software before feeding into a feature-based semi-supervised machine learning framework. The method is tested with data collected from an uncalibrated multibeam echosounder around an offshore gas platform in the Adriatic Sea. It resulted in more-efficient target detection, and, although uncertainties regarding user labelled training data need to be underlined, an accuracy of 98% in target classification was reached by using a final pre-trained stacking ensemble model.
Benthopelagic animals are an important component of the deep-sea ecosystem, yet are notoriously difficult to study. Multibeam echosounders (MBES) deployed on autonomous underwater vehicles (AUVs) ...represent a promising technology for monitoring this elusive fauna at relatively high spatial and temporal resolution. However, application of this remote-sensing technology to the study of small (relative to the sampling resolution), dispersed and mobile animals at depth does not come without significant challenges with respect to data collection, data processing and vessel avoidance. As a proof of concept, we used data from a downward-looking RESON SeaBat 7125 MBES mounted on a Dorado-class AUV to detect and characterise the location and movement of backscattering targets (which were likely to have been individual fish or squid) within 50 m of the seafloor at ~800 m depth in Monterey Bay, California. The targets were detected and tracked, enabling their numerical density and movement to be characterised. The results revealed a consistent movement of targets downwards away from the AUV that we interpreted as an avoidance response. The large volume and complexity of the data presented a computational challenge, while reverberation and noise, spatial confounding and a marginal sampling resolution relative to the size of the targets caused difficulties for reliable and comprehensive target detection and tracking. Nevertheless, the results demonstrate that an AUV-mounted MBES has the potential to provide unique and detailed information on the in situ abundance, distribution, size and behaviour of both individual and aggregated deep-sea benthopelagic animals. We provide detailed data-processing information for those interested in working with MBES water-column data, and a critical appraisal of the data in the context of aquatic ecosystem research. We consider future directions for deep-sea water-column echosounding, and reinforce the importance of measures to mitigate vessel avoidance in studies of aquatic ecosystems.
A large-scale oceanographic survey (BROKE-West) was undertaken off East Antarctica in the austral summer of 2005/06. Throughout the survey, multi-frequency echosounder data and ancillary ...environmental data were collected to determine the distribution and abundance of Antarctic krill (
Euphausia superba) and to explore its broad relationship with the bio-physical environment. The acoustic data were analysed using three different methods to provide measurements of krill abundance that can be set in context with previous studies. Based on the most recently developed acoustic method, the mean biomass-density of krill across the survey area (1.3 million km
2) was estimated to be 24
g
m
−2. Total biomass was estimated to be 28.75 million tonnes (Mt) with a coefficient of variation (CV) of 16.18%. This biomass estimate has been used by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) to update the precautionary catch limit for krill in this area (CCAMLR Division 58.4.2) from 0.450 to 2.645
Mt. Overall, krill were widely distributed at relatively low densities: 25% of the 2-km along-track echo-integration intervals were devoid of krill, 50% registered densities of 1
g
m
−2 of krill or less and 75% registered densities of 12
g
m
−2 or less. Mean densities were highest in the waters to the south of the Southern Boundary (SB) of the Antarctic Circumpolar Current (ACC), while the waters to the north of the Southern ACC Front (SACCF) were almost devoid of krill. Half of the cumulative krill density across the survey was found within 80
km of the 1000
m isobath (the shelf break), and 40% within 40
km. This was mostly due to particularly high densities (up to 4400
g
m
−2) around the shelf break on 3 of the 11 transects surveyed. The majority of acoustic krill detections were in the top 100
m of the water column, centred around 50
m depth.
Prey-field use by a Southern Ocean top predator Bedford, Merel; Melbourne-Thomas, Jessica; Corney, Stuart ...
Marine ecology. Progress series (Halstenbek),
04/2015, Letnik:
526
Journal Article
Recenzirano
Odprti dostop
An important challenge for understanding and managing marine ecosystems is determining the relationship between the distributions of prey species and the foraging of top predators. We examined the ...diet and foraging dynamics of breeding macaroni penguins Eudyptes chrysolophus from sub-Antarctic Heard Island and related these to prey distributions derived from active-acoustics and net-derived data in the foraging zone of the penguins. Consistent with previous findings, we found that penguin diets changed between the guard and crèche stages of the breeding cycle and that this change in diet corresponded with a switch from short foraging trips in the guard stage to significantly longer, offshore foraging trips in the crèche stage. We related these differences in diet and foraging to characteristics of the prey field—specifically, a relatively uniform distribution of krill over the shelf and in deeper, offshore waters, compared with an increasing abundance of fish further from shore. We developed a simple dynamic energy budget for macaroni penguins to explore whether targeting fish during the crèche stage was an energetically favourable strategy. Finally, we extrapolated our energy budget to estimate prey consumption at the colony scale as previous work has suggested that depletion near breeding colonies could contribute to prey switching. We found that prey switching during the crèche stage was energetically favourable and was most likely related to a reduction in foraging constraints, rather than prey depletion. This study shows the value of integrating data sets to address questions surrounding variation in diet and the use of alternative prey by marine predators.
Fieldwork was conducted at three contrasting sites to test the applicability of an in situ technique (ZOOFLUX) for the assessment of the role of zooplankton diel vertical migration (DVM) in the ...removal of carbon and nitrogen from the surface layer of the ocean to the depths (the active flux). ZOOFLUX relies on the detection of a significant dawn-dusk difference in the carbon and nitrogen weight of migrating individuals (δ). Therefore, its successful application is highly dependent upon the ecology of the migrant species, the level of individual variability in carbon and nitrogen weight (V), and the number of samples that can be collected (n).At site 1 (the Clyde Sea, western Scotland), Calanus finmarchicus and C. helgolandicus exhibited a variety of migration patterns, and did not always conform to the ‘normal’ DVM pattern of up at dusk and down at dawn (NDVM). As a result, δ was variable and V relatively high, while n was relatively low. When δ was non-significant, the probability of making a Type II statistical error (β) was high. In most cases, both the minimum number of samples ( nmin), and the minimum diel change occurring in carbon and nitrogen weight (δmin), would have needed to be unrealistically high before ZOOFLUX was applicable to these species.At site 2 (the Sargasso Sea off Bermuda), Pleuromamma xiphias and krill (Thysanopoda aequalis, Euphausia hemigibba, and E. brevis) both performed NDVM. At site 3 (Doubtful Sound, New Zealand), Nyctiphaties australis performed NDVM at the population level, but some individuals remained at depth during the night, and others at the surface during the day. Despite the more uniform pattern of NDVM at both of these sites, the findings were similar to those at site 1:δ was variable, V relatively high, and n relatively low. Again, this meant that nmin and δmin were often unrealistically high.These findings are discussed in terms of (1) what we can now say about the factors contributing to the active flux, (2) the applicability of the ZOOFLUX technique, and (3) the way forward for future studies. While the ZOOFLUX technique is advocated for future application, it will only prove successful with a prior knowledge of the DVM behaviour of the target species, and the ability to collect interzonal migrants at the critical moments at which they pass both up and down through the pycnocline during the diel cycle.
According to the author, rather than alleviating poverty, microfinance financialises poverty. By indebting poor people in the Global South, it drives financial expansion and opens new lands of ...opportunity for the crisis-ridden global capital markets. This book raises fundamental concerns about this widely-celebrated tool for social development.
This intervention responds to a series of articles—including one published in Antipode—on what is referred to as “new” state capitalism (NSC) or sometimes, simply, state capitalism. Our overarching ...argument is that by eliding state and institutionalist theory and, specifically, separating the analysis of state transformation from the power and leverage of social forces under late capitalism, NSC scholars end up offering an inaccurate, inchoate and incoherent conceptualisation and analysis of important phenomena. Our contention is that future work needs to return to socio‐relational analyses of the state, prioritising the power and leverage of social forces operating under patterns of accumulation characterised by more‐integrated‐than‐ever‐before global economic‐market relations and the concentration of productive and financial capital.
Large numbers of people are being discharged from hospital following COVID-19 without assessment of recovery. In 384 patients (mean age 59.9 years; 62% male) followed a median 54 days post discharge, ...53% reported persistent breathlessness, 34% cough and 69% fatigue. 14.6% had depression. In those discharged with elevated biomarkers, 30.1% and 9.5% had persistently elevated d-dimer and C reactive protein, respectively. 38% of chest radiographs remained abnormal with 9% deteriorating. Systematic follow-up after hospitalisation with COVID-19 identifies the trajectory of physical and psychological symptom burden, recovery of blood biomarkers and imaging which could be used to inform the need for rehabilitation and/or further investigation.
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