Research Vessel Research Articles

Site Fidelity of Coastal Bottlenose Dolphins (Tursiops truncatus) off Southeast Florida, USA

The coastal bottlenose dolphin is well studied throughout its natural range, though most research focuses on wide, well-protected habitats such as bays and estuaries rather than on narrow coastal sand banks. This study identifies a residential group of coastal bottlenose dolphins utilizing the northwestern Atlantic waters off the coast of Palm Beach County, Florida. From 2014 to 2020, 313 boat surveys were conducted, and 585 individual dolphins were identified using photo-identification. Using seasonal and annual resighting ratios, 24 dolphins were considered full-time residents, 66 dolphins were considered part-time residents, and 478 dolphins were transient. The presence of individuals with high site fidelity indicates that the region is used as a permanent habitat for some individuals, while the presence of transient animals may indicate a possible bridge between populations living to the north and south of the region.

Aerosol and atmospheric dynamics over the tropical Indian ocean: A study from the IInd international Indian Ocean expedition

The study addresses the aerosol distribution, boundary layer dynamics and associated shortwave radiative forcing over the Tropical Indian Ocean. The observations were carried out onboard Ocean Research Vessel Sagar Nidhi in December 2015 as a part of the International Indian Ocean Expedition-II (IIOE-II). The dominance of continentally originated aerosols was observed near the coast because of northeasterly winds, while marine aerosols abounded offshore. The uneven distribution of aerosols in the study region was due to varying atmospheric conditions triggered by various convective processes, wherein the convective available potential energy and convective inhibition energy ranged between 0.0274 and 2535.2 J kg−1 and 0 and -387.5 J kg−1, respectively. The atmospheric forcing varied in tandem with aerosol loading. It was evident from the high forcing values (17.98 W m−2) and corresponding heating rate of 0.504 K day−1 observed near the coast. The average heating rate in the far offshore (stations 6–10) region was 0.063 ± 0.017 K day−1, which amounted to an ∼87% decrease from the coastal location.

A note on vessel of opportunity sighting surveys for cetaceans in the shelf edge region off the southern coast of Brazil

Results are presented from vessel of opportunity sighting surveys conducted from 1996 to 1999 aboard the Fundação Universidade Federal do Rio Grande (FURG) Research Vessel Atlântico Sul off the southern Brazil coast (27°-35°S). These surveys were conducted in conjunction with a research sampling project (Argo) of the pelagic living resources within Brazil’s southern shelf and slope waters. The cruises entailed pelagic longlining and dedicated searching was conducted during hauling and setting operations as well as when the vessel was transiting. The sighting surveys represent the first attempt to collect quantitative information on the distribution and density of cetaceans in these waters. A total of 109 cetacean sightings were made during a total of 269 hours of dedicated searching effort covering approximately 2,200 miles. Sperm whales were the dominant species accounting for over 40% of the sightings and were concentrated in the slope area in the more southerly region. The high number and fidelity of the sperm whale sightings suggest the year around importance of the shelf border as a possible migration route and/or food resources ground. Killer whales were the second most commonly sighted species and were detected on all of the cruises. 44% of the killer whale sightings were detected during longline hauling or setting operations and observations suggest a positive attraction of killer whales to the vessel at these times. Also of particular interest during the spring cruise was a humpback and two minke whale sightings. Sightings in November-December in sub-tropical and temperate waters were unexpected for both of these species as the South Atlantic populations are generally considered to have fully migrated to Antarctic waters.

Tensor-based flow reconstruction from optimally located sensor measurements

Reconstructing high-resolution flow fields from sparse measurements is a major challenge in fluid dynamics. Existing methods often vectorize the flow by stacking different spatial directions on top of each other, hence confounding the information encoded in different dimensions. Here, we introduce a tensor-based sensor placement and flow reconstruction method which retains and exploits the inherent multidimensionality of the flow. We derive estimates for the flow reconstruction error, storage requirements and computational cost of our method. We show, with examples, that our tensor-based method is significantly more accurate than similar vectorized methods. Furthermore, the variance of the error is smaller when using our tensor-based method. While the computational cost of our method is comparable to similar vectorized methods, it reduces the storage cost by several orders of magnitude. The reduced storage cost becomes even more pronounced as the dimension of the flow increases. We demonstrate the efficacy of our method on three examples: a chaotic Kolmogorov flow, in situ and satellite measurements of the global sea surface temperature and three-dimensional unsteady simulated flow around a marine research vessel.

Mission Tara Microplastics: a holistic set of protocols and data resources for the field investigation of plastic pollution along the land-sea continuum in Europe.

The Tara Microplastics mission was conducted for 7months to investigate plastic pollution along nine major rivers in Europe-Thames, Elbe, Rhine, Seine, Loire, Garonne, Ebro, Rhone, and Tiber. An extensive suite of sampling protocols was applied at four to five sites on each river along a salinity gradient from the sea and the outer estuary to downstream and upstream of the first heavily populated city. Biophysicochemical parameters including salinity, temperature, irradiance, particulate matter, large and small microplastics (MPs) concentration and composition, prokaryote and microeukaryote richness, and diversity on MPs and in the surrounding waters were routinely measured onboard the French research vessel Tara or from a semi-rigid boat in shallow waters. In addition, macroplastic and microplastic concentrations and composition were determined on river banks and beaches. Finally, cages containing either pristine pieces of plastics in the form of films or granules, and others containing mussels were immersed at each sampling site, 1month prior to sampling in order to study the metabolic activity of the plastisphere by meta-OMICS and to run toxicity tests and pollutants analyses. Here, we fully described the holistic set of protocols designed for the Mission Tara Microplastics and promoted standard procedures to achieve its ambitious goals: (1) compare traits of plastic pollution among European rivers, (2) provide a baseline of the state of plastic pollution in the Anthropocene, (3) predict their evolution in the frame of the current European initiatives, (4) shed light on the toxicological effects of plastic on aquatic life, (5) model the transport of microplastics from land towards the sea, and (6) investigate the potential impact of pathogen or invasive species rafting on drifting plastics from the land to the sea through riverine systems.

Improving Safety of Marine Cable Survey Operation Through Safety Assessment using the Formal Safety Assessment Method (Case Study RV. Baruna Jaya)

In the last five years, survey operations for marine cables have become a yearly activity carried out by Indonesia’s Research Vessel. Safety in survey operations is one of the biggest concerns in marine cable route surveys. This paper focuses on handling the survey operation risk and excluding the vessel operation risk. To solve the problem, we need a risk analysis methodology with systematic steps to identify, prioritize, and control risks. The International Maritime Organization’s (IMO) methodology to deal with them is the Formal Safety Assessment (FSA). Firstly, Hazard Identification (HAZID) is used to identify hazards and prioritize Top Events where Towfish Survey Equipment Lost is found as the Highest Top Event with basic events Bad Communication, Fisheries Aggregating Device, Seabed Collision, and Wire & Cable fastening using the Fault Tree Analysis Method as the second step. Determining a Risk Control Option (RCO) based on the Basic Event in the FTA is the third step, of which Mitigation and Prevention will be the highlight. Lastly, RCO will be assessed according to Cost Benefit Assessment (CBA). The results showed that by using Administrative Risk Control Option, we could reduce the probability of survey equipment being lost by 46.55%.

Daily and Subdaily Wind and Divergence Variations Observed by a Shipborne Doppler Radar off the Southwestern Coast of Sumatra

Abstract This study investigated the daily cycle of the wind and divergence fields observed off the southwestern coast of Sumatra during a field campaign of the Years of the Maritime Continent pilot study. An algorithm was developed to retrieve kinematic variables from the single-Doppler data collected aboard the Research Vessel Mirai from 24 November to 13 December 2015. The observed daily cycles of the wind and divergence fields consisted of diurnal, semidiurnal, and short-term variations. Diurnal wind variation was characterized by deep and three-dimensional circulation. There was an approximate phase locking of the semidiurnal variation to the diurnal variation, both in the wind and divergence fields. The short-term wind variation occurred at a time scale of ∼1–3 h, and this pattern was associated with density currents or mesoscale gravity waves. Up to 73% of the daily vertical motion variance can be attributed to the diurnal and semidiurnal vertical motion variations with comparable strengths. Concurrently, precipitation propagated offshore in phase with density currents and mesoscale gravity waves. Our results suggest that diurnal and semidiurnal wind variations dominate the daily evolution of precipitation, whereas density currents and mesoscale gravity waves control offshore propagation. Additionally, it appears that the daily precipitation cycle is modulated by multiple-time-scale wind variabilities of less than a day, which is also responsible for the development of strong nocturnal convection off the southwestern coast of Sumatra. Significance Statement To improve our understanding of the daily wind and divergence cycle off the southwestern coast of Sumatra, we examined wind data collected by a shipborne Doppler radar. The observed daily cycles of the wind and divergence fields consisted of diurnal and semidiurnal variations, as well as a 1–3-h variation associated with a density current or mesoscale gravity wave. Our results suggest that diurnal and semidiurnal wind variations dominate the daily evolution of precipitation, whereas density currents and mesoscale gravity waves control offshore propagation. Thus, we highlight the role of multiple-time-scale wind variabilities of less than a day in modulating the daily precipitation cycle off the southwestern coast of Sumatra.

The Structure of the Zooplankton Community in Spitsbergen Waters during the Winter Period

The plankton community was collected during the winter season from the Isfjord aquatic area, on the western coast of Spitsbergen Island, during the interval November 30 to December 6, 2015. Sampling was carried out with a plankton net and bathometric catches on board of the research vessel Dalnie Zelentsy. The assemblages of micro- and mesoplankton from several aquatic areas of the central part of Isfjord have been studied qua-litatively and quantitatively. These areas contain waters with different hydrological structures. We noted that the number of nauplii of small copepods in samples varied significantly depending on sampling method. The main emphasis of this research is placed on the methodology of plankton study in the Arctic waters during winter seasons.

Uncrewed surface systems facilitating a new era of global ocean exploration

There is growing recognition that key to addressing critical issues like climate change, global sea level rise and the long-term sustainability of humankind is a more complete understanding of our oceans and processes within them that account for the distribution of global heat, CO2 and provide sustenance to so many. Yet, despite years of effort, less than 25% of the global ocean seafloor has been mapped and less than 5% of the ocean volume explored, likely due to the cost and inefficiency of traditional ocean mapping and exploration techniques using large, very expensive, crewed research vessels. Recent advances in the development of uncrewed surface vessels offer the possibility to reduce costs and increase efficiency of ocean mapping and exploration. Such efficiencies can be gained by using small mother ship-deployed uncrewed vessels acting as relatively inexpensive mapping and sampling force multipliers or the use of small uncrewed vessels launched to from a mother ship to monitor and control autonomous underwater vehicles, allowing multiple operations simultaneously and “verified, directed sampling”, all while freeing the mother ship for independent operations. We are also seeing the development of larger uncrewed vessels launched from shore with long-endurance and range, capable of carrying a full suite of deep ocean mapping and exploration tools. All of these systems and approaches offer great hope but it is very early in our understanding of their full capabilities, costs and limitations and we must be careful not to overpromise, leading to disappointments and early abandonment of a potentially innovative approach, while at the same time maintaining the patience required to continue the research, investment and innovation that will hopefully bring us to a new world of efficient and effective ocean mapping and exploration that will allow us to meet our goal of complete coverage of the ocean.

Ocean cross-validated observations from R/Vs L'Atalante, Maria S. Merian, and Meteor and related platforms as part of the EUREC4A-OA/ATOMIC campaign

Abstract. The northwestern Tropical Atlantic Ocean is a turbulent region, filled with mesoscale eddies and regional currents. In this intense dynamical context, several water masses with thermohaline characteristics of different origins are advected, mixed, and stirred at the surface and at depth. The EUREC4A-OA/ATOMIC experiment that took place in January and February 2020 was dedicated to assessing the processes at play in this region, especially the interaction between the ocean and the atmosphere. For that reason, four oceanographic vessels and different autonomous platforms measured properties near the air–sea interface and acquired thousands of upper-ocean (up to 400–2000 m depth) profiles. However, each device had its own observing capability, varying from deep measurements acquired during vessel stations to shipboard underway near-surface observations and measurements from autonomous and uncrewed systems (such as Saildrones). These observations were undertaken with a specific sampling strategy guided by near-real-time satellite maps and adapted every half day, based on the process that was investigated. These processes were characterized by different spatiotemporal scales, from mesoscale eddies, with diameters exceeding 100 km, to submesoscale filaments of 1 km width. This article describes the datasets gathered from the different devices and how the data were calibrated and validated. In order to ensure an overall consistency, the platforms' datasets are cross-validated using a hierarchy of instruments defined by their own specificity and calibration procedures. This has enabled the quantification of the uncertainty in the measured parameters when different datasets are used together, e.g., https://doi.org/10.17882/92071 (L'Hégaret et al., 2020a).

Bayesian geoacoustic inversion in shallow water with vertical coherence of ship-radiated noise

Spatial structure of underwater acoustic field depends strongly on the geoacoustic properties of the seabed. The geoacoustic parameters can be estimated using the spatial coherence dominated by a single broadband source. In this paper, geoacoustic inversion of a shallow water environment is carried out using the vertical coherence of ship-radiated noise at a close range. Data were measured in an experiment in the South China Sea, and the vertical coherence is extracted from a single hydrophone pair in the vertical line array. The closest point of the passing research ship approach is determined first, and then the broadband coherence curves are extracted as the input for the inversion algorithm. Due to the lack of an appropriate parametrization, the trans-dimensional inversion method combined with the auto-regressive error model is adopted in this paper. The inversion results show that the sound speed is the most sensitive, followed by the density, and then the attenuation coefficient is the least sensitive, which is consistent with previous works. The data error hypothesis is verified via a posterior examinations.

Observations of Offshore Internal Boundary Layers

AbstractThe growth of the marine internal boundary layer (MIBL, height hi) with the shore‐normal distance x, is a topic of continuing interest because of its applications in coastal pollution dispersion, offshore wind farm siting, coastal air‐sea fluxes and in evaporative ducting. Available data on MIBL are scarce, given the difficulty of measuring the variability of coastal winds. During the Coupled Air‐Sea Processes and Electromagnetic Research campaigns, an array of instrumentation was deployed to measure offshore spatial variability and its effect on electromagnetic (EM) wave propagation. Meteorological sensors (flux towers and remote sensing) deployed along the coast of Point Mugu, California, on a research vessel and FLoating Instrument Platform provided surface layer and boundary layer observations. Measurements from multiple remote sensors such as synchronized triple Doppler lidars, small boat operations with tethered lifting system, and radiosondes provided a holistic view of the MIBL growth and its spatial variability in coastal areas. Convective and stable MIBL observed during two intensive operating period days showed distinct growth characteristics off the coast of Point‐Mugu. During stable stratified atmospheric conditions, an MIBL was observed to develop least as far as 47 km from the coast. The growth of MIBL within the nearshore adjustment zone was influenced by surrounding atmospheric, oceanographic, and topographic conditions. A parameterization scheme is developed based on advection‐diffusion balance equations, accounting for upstream turbulence, and compared with hi observations from a Doppler lidar and profiles taken from a small boat. An evaluation of existing IBL theories is also conducted.

SituSeq: an offline protocol for rapid and remote Nanopore 16S rRNA amplicon sequence analysis

Microbiome analysis through 16S rRNA gene sequencing is a crucial tool for understanding the microbial ecology of any habitat or ecosystem. However, workflows require large equipment, stable internet, and extensive computing power such that most of the work is performed far away from sample collection in both space and time. Performing amplicon sequencing and analysis at sample collection would have positive implications in many instances including remote fieldwork and point-of-care medical diagnoses. Here we present SituSeq, an offline and portable workflow for the sequencing and analysis of 16S rRNA gene amplicons using Nanopore sequencing and a standard laptop computer. SituSeq was validated by comparing Nanopore 16S rRNA gene amplicons, Illumina 16S rRNA gene amplicons, and Illumina metagenomes, sequenced using the same environmental DNA. Comparisons revealed consistent community composition, ecological trends, and sequence identity across platforms. Correlation between the abundance of taxa in each taxonomic level in Illumina and Nanopore data sets was high (Pearson’s r > 0.9), and over 70% of Illumina 16S rRNA gene sequences matched a Nanopore sequence with greater than 97% sequence identity. On board a research vessel on the open ocean, SituSeq was used to analyze amplicon sequences from deep sea sediments less than 2 h after sequencing, and 8 h after sample collection. The rapidly available results informed decisions about subsequent sampling in near real-time while the offshore expedition was still underway. SituSeq is a portable and user-friendly workflow that helps to bring the power of microbial genomics and diagnostics to many more researchers and situations.

Prospects for the pink salmon fishery in the Russian waters of the Bering and Okhotsk Seas in 2023 based on analysis of trawl surveys of the juveniles aboard RV TINRO and RV Professor Kaganovsky in autumn 2022

Modern technique of counting pink salmon juveniles in trawl surveys by two research vessels simultaneously makes it possible to cover the surveyed area in a short time that excludes repeated counts of actively migrating fish at adjacent transects. Such survey in the fall of 2022 was conducted jointly by RV TINRO and RV Professor Kaganovsky. The main aggregations of pink salmon in the offshore areas of the Bering and Okhotsk Seas were accounted that guaranteed reliability of the primary materials for prediction of the pink salmon return and catches in 2023. Two regional groups of pink salmon were separated in the mixed aggregation of juveniles in the Okhotsk Sea using the method of EM-clustering; the ratio of «northern» and «southern» complexes of their local stocks was determined as 55 : 45 %. The total number of pink salmon was assessed as 0.94 ∙ 109 ind. in the Bering Sea and 2.70 ∙ 109 ind. in the Okhotsk Sea. Expected return of pink salmon in 2023 was preliminary estimated as 200 ∙ 106 ind. for the Bering Sea and at least 270 ∙ 106 ind. for the Okhotsk Sea.

Surface impacts and associated mechanisms of a moisture intrusion into the Arctic observed in mid-April 2020 during MOSAiC

Distinct events of warm and moist air intrusions (WAIs) from mid-latitudes have pronounced impacts on the Arctic climate system. We present a detailed analysis of a record-breaking WAI observed during the MOSAiC expedition in mid-April 2020. By combining Eulerian with Lagrangian frameworks and using simulations across different scales, we investigate aspects of air mass transformations via cloud processes and quantify related surface impacts. The WAI is characterized by two distinct pathways, Siberian and Atlantic. A moist static energy transport across the Arctic Circle above the climatological 90th percentile is found. Observations at research vessel Polarstern show a transition from radiatively clear to cloudy state with significant precipitation and a positive surface energy balance (SEB), i.e., surface warming. WAI air parcels reach Polarstern first near the tropopause, and only 1–2 days later at lower altitudes. In the 5 days prior to the event, latent heat release during cloud formation triggers maximum diabatic heating rates in excess of 20 K d-1. For some poleward drifting air parcels, this facilitates strong ascent by up to 9 km. Based on model experiments, we explore the role of two key cloud-determining factors. First, we test the role moisture availability by reducing lateral moisture inflow during the WAI by 30%. This does not significantly affect the liquid water path, and therefore the SEB, in the central Arctic. The cause are counteracting mechanisms of cloud formation and precipitation along the trajectory. Second, we test the impact of increasing Cloud Condensation Nuclei concentrations from 10 to 1,000 cm-3 (pristine Arctic to highly polluted), which enhances cloud water content. Resulting stronger longwave cooling at cloud top makes entrainment more efficient and deepens the atmospheric boundary layer. Finally, we show the strongly positive effect of the WAI on the SEB. This is mainly driven by turbulent heat fluxes over the ocean, but radiation over sea ice. The WAI also contributes a large fraction to precipitation in the Arctic, reaching 30% of total precipitation in a 9-day period at the MOSAiC site. However, measured precipitation varies substantially between different platforms. Therefore, estimates of total precipitation are subject to considerable observational uncertainty.

A human cyber-physical system for human-centered computing in seafaring

Human cyber-physical systems present an appealing platform for facilitating human-centered computing, particularly in environments where humans are required to interact with systems comprised of cyber and physical layers. Universally accepted elements of a human cyber-physical system, and interactions among these elements, do not appear to emerge in literature. To address this, a human cyber-physical system architecture is offered, led by the seafaring focus of this study. A human cyber-physical system implementation, called Mariner 4.0, for monitoring motion sickness of seafarers is presented to demonstrate the operation of a human cyber-physical system as a platform for human-centered computing. The human cyber-physical system implementation enabled the digital representation of the state of motion sickness and location of a seafarer, and conveyance of related information through a state monitor display. Using data captured on board South Africa’s polar supply and research vessel, the SA Agulhas II, results showed that the human cyber-physical system incorporated location-specific variation in motion exposure experienced between two seafarers in motion sickness computations through facilitating individualized data acquisition and integration.

MARINER 4.0: INTEGRATING SEAFARERS INTO A MARITIME 4.0 ENVIRONMENT

Digitalisation of systems and processes in the maritime industry are spurring Maritime 4.0, a digital transformation promising enormous gains, including improved design processes and reduced operational costs. Gleaning inter-disciplinary proficiency from Operator 4.0 in manufacturing, the present work seeks to introduce the Mariner 4.0 – a seafaring passenger or crew member with technologically augmented skills. This research aims to realise Mariner 4.0 through a human digital twin solution – a virtual representation of the state and behaviour of a unique individual over time – for seafarers on South Africa’s polar research and supply vessel, the SA Agulhas II. This paper presents human-related challenges identified within seafaring vessels, the expected value of human digital twin solutions for the maritime industry, the development of a human digital twin solution to integrate seafarers into a Maritime 4.0 environment (i.e. the development of Mariner 4.0), and an illustrative use case focussing on human comfort monitoring and management.

Reducing Southern Ocean Shortwave Radiation Errors in the ERA5 Reanalysis with Machine Learning and 25 Years of Surface Observations

Abstract Earth system models struggle to simulate clouds and their radiative effects over the Southern Ocean, partly due to a lack of measurements and targeted cloud microphysics knowledge. We have evaluated biases of downwelling shortwave radiation in the ERA5 climate reanalysis using 25 years (1995–2019) of summertime surface measurements, collected on the Research and Supply Vessel (RSV) Aurora Australis, the Research Vessel (R/V) Investigator, and at Macquarie Island. During October–March daylight hours, the ERA5 simulation of SWdown exhibited large errors (mean bias = 54 W m−2, mean absolute error = 82 W m−2, root-mean-square error = 132 W m−2, and R2 = 0.71). To determine whether we could improve these statistics, we bypassed ERA5’s radiative transfer model for SWdown with machine learning–based models using a number of ERA5’s gridscale meteorological variables as predictors. These models were trained and tested with the surface measurements of SWdown using a 10-fold shuffle split. An extreme gradient boosting (XGBoost) and a random forest–based model setup had the best performance relative to ERA5, both with a near complete reduction of the mean bias error, a decrease in the mean absolute error and root-mean-square error by 25% ± 3%, and an increase in the R2 value of 5% ± 1% over the 10 splits. Large improvements occurred at higher latitudes and cyclone cold sectors, where ERA5 performed most poorly. We further interpret our methods using Shapley additive explanations. Our results indicate that data-driven techniques could have an important role in simulating surface radiation fluxes and in improving reanalysis products. Significance Statement Simulating the amount of sunlight reaching Earth’s surface is difficult because it relies on a good understanding of how much clouds absorb and scatter sunlight. Relative to summertime surface observations, the ERA5 reanalysis still overestimates the amount of sunlight entering the Southern Ocean. We taught some models how to predict the amount of sunlight entering the Southern Ocean using 25 years of surface observations and a small set of meteorological variables from ERA5. By bypassing the ERA5’s internal simulation of the absorption and scattering of sunlight, we can drastically reduce biases in the predicted surface shortwave radiation. Large improvements in cold sectors of cyclones and closer to Antarctica were observed in regions where many numerical models struggle to simulate the amount of incoming sunlight correctly.

Southern coastal system of the San Jorge Gulf during spring

The San Jorge Gulf was declared an area of national economic, commercial, conservation and diversity interest. To contribute to its study, the southern coastal sector of the gulf was characterised in physical and chemical parameters in spring campaigns (November 2016 and 2017). Samples were taken on board the oceanographic vessel Puerto Deseado in three perpendicular to the coast transects and another one to the southeast of the gulf, which crosses a thermohaline front. The perpendicular to the coast transects showed a similar pattern of distribution of physical and chemical properties in the water column. At nearshore stations, the water column was homogeneous and the nutrient concentrations between the surface and bottom layers were similar. At offshore stations, the water column was stratified and the nutrient concentrations were higher near the bottom than at surface. In 2016, a wind induced upwelling front was observed in the southwest of the gulf. Both sides of the thermohaline front did not show significant chemical differences. Throughout the study area, silicic acid and nitrate limited primary production. Satellite chlorophyll-a data and fluorescence profiles showed that the southern sector of the gulf has a high biomass of phytoplankton during November. We conclude that the southern sector of the SJG has different features depending on the external forcing caused by the front. The presence of fronts stimulates the growth of phytoplankton biomass through the injection of nutrients from the homogeneous part to the stratified sector. This would affect phytoplankton community and, thus, the productivity of the system.

Discovery of a suburban wetland refuge for a depleted American crocodile (Crocodylus acutus) population in northwestern Mexico, using a commercial Unmanned Aerial Vehicle

Background and Research Aims The Urías Coastal Lagoon (UCL) is a heavily modified and polluted lagoon near Mazatlán, in northwestern Mexico. Once abundant in the UCL, the American crocodile ( Crocodylus acutus) is now rarely seen in the area. A healthy population of apex predators is essential to maintain the trophic balance of ecosystems. Our research aim was to lay the groundwork for studies of American crocodile population ecology in the UCL. Methods Traditional boat surveys (day and night) of crocodiles were undertaken in the UCL in May-July 2022. Two exploratory aerial (∼ 30 m altitude) surveys of a small wetland located close to a habitational complex in the vicinity of the UCL were performed in June and December 2022, using a commercial Unmanned Aerial Vehicle (UAV). We used images obtained with the UAV to estimate the size of the crocodiles detected in the wetland. Results This study confirms the presence of American crocodiles in the UCL and presents the first information on individuals of this species for this area. Aerial surveys revealed the presence of 17 individuals in the wetland; the mean size of nine of those individuals was 183.3 ± 60 cm (range: 130-310 cm). Two yearlings (∼37 cm length), possibly born in June 2022, were captured in the same wetland in September 2022. We also surveyed 50.7 km of UCL coastline by boat, but no crocodiles were sighted. Conclusion The crocodiles seem to avoid the human-impacted UCL and likely use the less impacted surrounding wetlands as a refuge area, which they also use to reproduce. The presence of both yearlings and adults is a good sign for the survival of this vulnerable population. Implications for Conservation We believe that the surveyed wetland should be closely monitored for conservation purposes because it might be one of the last crocodile breeding refuges in the heavily modified and polluted coastal environment of the UCL. We summarize our results with a series of recommendations for local and federal authorities. These recommendations would likely help the conservation of the American crocodile population in the UCL.