Maritime vessel classification to monitor fisheries with SAR: demonstration in the North Sea

Integration of methods based on satellite remote sensing into current maritime monitoring strategies could help tackle the problem of global overfishing. Operational software is now available to perform vessel detection on satellite imagery, but research on vessel classification has mainly focused on bulk carriers, container ships, and oil tankers, using high-resolution commercial Synthetic Aperture Radar (SAR) imagery. Here, we present a method based on Random Forest (RF) to distinguish fishing and non-fishing vessels, and apply it to an area in the North Sea. The RF classifier takes as input the vessel’s length, longitude, and latitude, its distance to the nearest shore, and the time of the measurement (am or pm). The classifier is trained and tested on data from the Automatic Identification System (AIS). The overall classification accuracy is 91%, but the precision for the fishing class is only 58% because of specific regions in the study area where activities of fishing and non-fishing vessels overlap. We then apply the classifier to a collection of vessel detections obtained by applying the Search for Unidentified Maritime Objects (SUMO) vessel detector to the 2017 Sentinel-1 SAR images of the North Sea. The trend in our monthly fishing-vessel count agrees with data from Global Fishing Watch on fishing-vessel presence. These initial results suggest that our approach could help monitor intensification or reduction of fishing activity, which is critical in the context of the global overfishing problem

An assessment of MODIS products in the Southern Ocean using tagged southern elephant seals, in the context of an increasingly positive Southern Annular Mode

The Southern Ocean maintains a complex, dynamic marine food web based on its stock of photosynthesising phytoplankton. For the same reason, it is our most significant sink of carbon, vital to functioning of global atmospheric systems. However, this key polar ocean is also responsive to atmospheric variability dominated by the Southern Annular Mode (SAM), with unknown implications for phytoplankton patterns in space and over time. MODIS surface chlorophyll-a concentration ([Chl-a]) and the depth of the 1% light level (Z[sub]eu) were evaluated against in situ fluorescence and light data collected by tagged southern elephant seals. Light data were processed to minimize self-shading and environmental sources of variability, and Lee Z[sub]eu outperformed Morel Z[sub]eu when examined relative to the resultant in situ measures of the 1% light level. Based on these results, fluorescence data were corrected for quenching at the surface using Lee Z[sub]eu as a reference depth; conserving deep chlorophyll maxima within hydrographically defined mixed layers. [Chl-a] was evaluated against quenching-corrected fluorescence and satellite products mirrored in situ trends over time. The MODIS timeseries was interrogated for spatio-temporal shifts to phytoplankton abundance in surface waters. Trends over 13 years of austral summers point to overall declines and perturbations to the timing of the bloom, with changes that were significantly related to the SAM presenting as regional rather than annular. In this context, to assess if perturbations may impact top predators, the at-sea behaviour of tagged seals were examined relative to the fluorescence and light data they collected. Using a cumulative sums analysis of speed, foraging phases were distinguishable from ’outbound’ and ’homebound’ travel. When all phases were examined relative to fluorescence and the 1% light level, foraging appeared to be associated with increased phytoplankton abundance. This suggests that the future of these marine predators may be linked to shifting phytoplankton patterns

Linking foraging behaviour of post-breeding adult female elephant seals from Marion Island to physical dynamics and productivity at the South-West Indian Ridge

Advances in remote sensing and tagging technology have made it possible to investigate the relationship between oceanographic dynamics and the distribution of certain marine species. For this study, surface chlorophyII-a concentration was used as a proxy for underlying related productivity, rather than as a direct indicator of prey density. Post-breeding, adult female southern elephant seals from Marion Island were tagged with conductivity, temperature and depth satellite-relayed data loggers (CTD-SRDL's) and their foraging behaviour was examined in relation to different chlorophyII-a concentrations. Optimal foraging and area restricted search theories predict that travelling speed and turning frequency would be quantifiably affected by prey density, which is in turn affected by the underlying richness of primary producers

Experimental determination of reflectance spectra of Antarctic krill (Euphausia superba) in the Scotia Sea

Antarctic krill are the dominant metazoan in the Southern Ocean in terms of biomass; however, their wide and patchy distribution means that estimates of their biomass are still uncertain. Most currently employed methods do not sample the upper surface layers, yet historical records indicate that large surface swarms can change the water colour. Ocean colour satellites are able to measure the surface ocean synoptically and should theoretically provide a means for detecting and measuring surface krill swarms. Before we can assess the feasibility of remote detection, more must be known about the reflectance spectra of krill. Here, we measure the reflectance spectral signature of Antarctic krill collected in situ from the Scotia Sea and compare it to that of in situ water. Using a spectroradiometer, we measure a strong absorption feature between 500 and 550 nm, which corresponds to the pigment astaxanthin, and high reflectance in the 600–700 nm range due to the krill's red colouration. We find that the spectra of seawater containing krill is significantly different from seawater only. We conclude that it is tractable to detect high-density swarms of krill remotely using platforms such as optical satellites and unmanned aerial vehicles, and further steps to carry out ground-truthing campaigns are now warranted

A Review of the Tools Used for Marine Monitoring in the UK: Combining Historic and Contemporary Methods with Modeling and Socioeconomics to Fulfill Legislative Needs and Scientific Ambitions

Marine environmental monitoring is undertaken to provide evidence that environmental management targets are being met. Moreover, monitoring also provides context to marine science and over the last century has allowed development of a critical scientific understanding of the marine environment and the impacts that humans are having on it. The seas around the UK are currently monitored by targeted, impact-driven, programmes (e.g., fishery or pollution based monitoring) often using traditional techniques, many of which have not changed significantly since the early 1900s. The advent of a new wave of automated technology, in combination with changing political and economic circumstances, means that there is currently a strong drive to move toward a more refined, efficient, and effective way of monitoring. We describe the policy and scientific rationale for monitoring our seas, alongside a comprehensive description of the types of equipment and methodology currently used and the technologies that are likely to be used in the future. We contextualize the way new technologies and methodologies may impact monitoring and discuss how whole ecosystems models can give an integrated, comprehensive approach to impact assessment. Furthermore, we discuss how an understanding of the value of each data point is crucial to assess the true costs and benefits to society of a marine monitoring programme

An alternative method for correcting fluorescence quenching

This work received funding from the MASTS pooling initiative (The Marine Alliance for Science and Technology for Scotland) and their support is gratefully acknowledged. MASTS is funded by the Scottish Funding Council (grant reference HR09011) and contributing institutions.Under high light intensity, phytoplankton protect their photosystems from bleaching through non-photochemical quenching processes. The consequence of this is suppression of fluorescence emission, which must be corrected when measuring in situ yield with fluorometers. We present data from the Southern Ocean, collected over five austral summers by 19 southern elephant seals tagged with fluorometers. Conventionally, fluorescence data collected during the day (quenched) were corrected using the limit of the mixed layer, assuming that phytoplankton are uniformly mixed from the surface to this depth. However, distinct deep fluorescence maxima were measured in approximately 30% of the night (unquenched) data. To account for the evidence that chlorophyll is not uniformly mixed in the upper layer, we propose correcting from the limit of the euphotic zone, defined as the depth at which photosynthetically available radiation is ~ 1% of the surface value. Mixed layer depth exceeded euphotic depth over 80% of the time. Under these conditions, quenching was corrected from the depth of the remotely derived euphotic zone Zeu, and compared with fluorescence corrected from the depth of the density-derived mixed layer. Deep fluorescence maxima were evident in only 10% of the day data when correcting from mixed layer depth. This was doubled to 21% when correcting from Zeu, more closely matching the unquenched (night) data. Furthermore, correcting from Zeu served to conserve non-uniform chlorophyll features found between the 1% light level and mixed layer depth.Publisher PDFPublisher PDFPeer reviewe

Evaluating merged Zeu products in the Southern Ocean for application towards an optimised fluorescence quenching correction method.

It is common practice to infer the size structure of phytoplankton communities in situ from either diagnostic pigments, estimated by High Performance LiquidChromatography (HPLC), or through size-fractionated filtration (SFF). In thispresentation, the three-component model of Brewin et al. (2010) was fitted tocoincident data from HPLC and from SFF collected along Atlantic Meridional Transect cruises. Both HPLC and SFF data supported the conceptual framework of the threecomponent model, but the fitted model parameters differed for the two datasets. The three-component model was extended to a multi-component model of size structure using observed relationships between model parameters and assuming that the asymptotic concentration that can be reached by cells increased linearly with increase in the upper bound on the cell size. The multi-component model was verified using independent SFF data for a variety of size-fractions along the AMT transect and found to perform well (0.628 < r < 0.989) lending support for the underlying assumptions. An advantage of the multi-component model over the three-component model is that, for the same number of parameters, it can be applied to any size range in a continuous fashion

Hyperspectral plastics dataset supplementary to the paper ‘Advancing floating plastic detection from space using hyperspectral imagery’

This database is the supplementary material of Tasseron et al., (2021): Advancing floating plastic detection from space using hyperspectral imagery