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- Multidisciplinary estimates of connectivity and population structure suggest the use of multiple units for the conservation and management of meagre, Argyrosomus regiusPublication . Abecasis, David; Ogden, R.; Winkler, Alexander; Gandra, Miguel; Khallahi, B.; Diallo, M.; Cabrera-Castro, R.; Weiller, Y.; Erzini, Karim; Afonso, P.; Assis, JorgeInformation on population structure and connectivity of targeted species is key for proper implementation of spatial conservation measures. We used a combination of genomics, biophysical modelling, and biotelemetry to infer the population structure and connectivity of Atlantic meagre, an important fisheries resource throughout its distribution. Genetic samples from previously identified Atlantic spawning locations (Gironde, Tejo, Guadalquivir, Banc d'Arguin) and two additional regions (Algarve and Senegal) were analysed using genome-wide SNP-genotyping and mitochondrial DNA analyses. Biophysical models were conducted to investigate larval dispersal and connectivity from the known Atlantic spawning locations. Additionally, thirteen fish were double-tagged with biotelemetry transmitters off the Algarve (Portugal) to assess movement patterns and connectivity of adult individuals. This multidisciplinary approach provided a robust overview of meagre population structure and connectivity in the Atlantic. Nuclear SNP-genotyping showed a clear differentiation between the European and African populations, with significant isolation of the few known Atlantic spawning sites. The limited level of connectivity between these subpopulations is potentially driven by adults, capable of wide-ranging movements and connecting sites 500 km apart, as evidenced by tagging studies, whilst larval dispersal inferred by modelling is much more limited (average of 52 km; 95% of connectivity events up to 174 km). Our results show sufficient evidence of population structure, particularly between Africa and Europe but also within Europe, for the meagre to be managed as separate stocks. Additionally, considering the low degree of larvae connectivity, the implementation of marine protected areas in key spawning sites could be crucial towards species sustainability.
- The multi-annual residency of juvenile smooth hammerhead shark in an oceanic island nurseryPublication . Afonso, Pedro; Gandra, Miguel; Graça, Gonçalo; Macena, Bruno; Vandeperre, Frederic; Fontes, JorgeThe increased risk of local extinction becomes critical for sharks depending on the narrow and isolated coastal habitats of oceanic islands. This includes large pelagic oceanic sharks that use such habitats as nurseries, as previously hypothesized for the smooth hammerhead Sphyrna zygaena, the least known of cosmopolitan large hammerhead sharks. We used a combination of acoustic and satellite telemetry in a juvenile population of Faial and Pico islands, Azores, mid-north Atlantic, to confirm if this isolated archipelago holds nurseries, and to answer questions related to their function and spatial-temporal stability. Our long-term acoustic tracking data showed a cluster of individual core home ranges in specific areas of north shore Faial, and surface positions from five Argos-linked tagged individuals also showed a clustering overlap in those areas for up to 1 year. These patterns seem to reveal a true habitat preference within the Faial-Pico island (sub) population of juvenile smooth hammerhead shark, and thus constitute strong evidence for this area to be considered a nursery. Some individuals remained in this nursery for up to 4 years, especially during summers. Sharks also showed a strong diel behavior, typically using the inshore nurseries during the day and moving further offshore during the night, during which they increased activity and dove deeper, most possibly to feed. We speculate that a combination of increased feeding opportunities, expanded trophic niche, and reduced predatory pressure may be a key evolutionary driver for the existence, prolonged use, and even preference of coastal nurseries at oceanic islands by juvenile smooth hammerhead shark. Given that these nurseries may constitute essential fish habitat for this species, they should be explicitly included in spatial management measures at the local and regional scales, as they may also play a role of greater importance to the north Atlantic population of this oceanic species.
- Weak biodiversity connectivity in the European network of no-take marine protected areasPublication . Assis, J.; Fragkopoulou, Eliza; Serrão, Ester A.; e Costa, Horta; Gandra, Miguel; Abecasis, DavidThe need for international cooperation in marine resource management and conservation has been reflected in the increasing number of agreements aiming for effective and well-connected networks of Marine Protected Areas (MPAs). However, the extent to which individual MPAs are connected remains mostly unknown. Here, we use a biophysical model tuned with empirical data on species dispersal ecology to predict connectivity of a vast spectrum of biodiversity in the European network of marine reserves (i.e., no-take MPAs). Our results highlight the correlation between empirical propagule duration data and connectivity potential and show weak network connectivity and strong isolation for major ecological groups, resulting from the lack of direct connectivity corridors between reserves over vast regions. The particularly high isolation predicted for ecosystemstructuring species (e.g., corals, sponges, macroalgae and seagrass) might potentially undermine biodiversity conservation efforts if local retention is insufficient and unmanaged populations are at risk. Isolation might also be problematic for populations' persistence in the light of climate change and expected species range shifts. Our findings provide novel insights for management directives, highlighting the location of regions requiring additional marine reserves to function as stepping-stone connectivity corridors. (C) 2021 Elsevier B.V. All rights reserved.
- Long-term intra and interspecific spatial overlap of Sphyraena viridensis and Seriola rivoliana at remote seamountsPublication . Gandra, Miguel Mena Matos; Erzini, KarimSpace use sharing and biological interactions can play an important role in determining individual habitat use and population spatial dynamics. Individuals often aggregate to enhance foraging efficiency, for protection against predators or to increase reproductive success. However, this behaviour also makes them more vulnerable to fishing and overexploitation. Seamounts, in particular, are known to concentrate large aggregations of pelagic reef fishes, and therefore deserve special attention and effective management schemes. The yellowmouth barracuda (Sphyraena viridensis) and the almaco jack (Seriola rivoliana) are two pelagic predators that commonly inhabit these offshore ecosystems in the Azores islands (central North Atlantic), where they are explored by the local artisanal fishing fleet. Yet, until very recently, little was known about their spatial ecology, with most published studies focusing rather on biological /physiological aspects or simply reporting presence records. Therefore, the objective of the present thesis was to use presence-absence datasets collected through passive acoustic telemetry in order to investigate yellowmouth barracuda and almaco jacks space use sharing and activity patterns. After developing a novel quantitative analysis based on fine-scale spatiotemporal overlap and null model randomization tests, evidence of non-random association was found, not only among conspecifics but also between individuals of the two species. Furthermore, tagged animals exhibited both diel and seasonal changes in habitat use. While yellowmouth barracuda are probably diurnal foragers, almaco jacks are probably more active during the night period, which might reduce interspecific competition pressure and increase the tolerance for niche overlap. Although year-round residents, both species seem to overlap more during the spawning season, which takes place from mid spring to late summer. Monthly fluctuations in spatial overlap were found to be significantly correlated with sea surface temperature and geostrophic current velocity. Additionally, we also found evidence of size-related differences in spatial behaviour of almaco jacks, with similarly-sized individuals overlapping more often and larger specimens being more infrequently detected. Overall, these results highlight the importance of effective local scale management to ensure the sustainability of these two iconic predators and open the door to further studies on social behaviour and habitat interconnectivity. To our knowledge, the developed method is the first to quantitatively assess animals’ spatiotemporal overlaps using solely presence/absence data from passive acoustic telemetry and, therefore, we believe it has potentially wide application in marine behavioural studies.
- Residency and space use estimation methods based on passive acoustic telemetry dataPublication . Kraft, Sebastian; Gandra, Miguel; Lennox, R. J.; Mourier, J.; Winkler, Alexander; Abecasis, DavidAcoustic telemetry has helped overcome many of the challenges faced when studying the movement ecology of aquatic species, allowing to obtain unprecedented amounts of data. This has made it into one of the most widely used methods nowadays. Many ways to analyse acoustic telemetry data have been made available and deciding on how to analyse the data requires considering the type of research objectives, relevant properties of the data (e.g., resolution, study design, equipment), habits of the study species, researcher experience, among others. To ease this decision process, here we showcase (1) some of the methods used to estimate pseudo-positions and positions from raw acoustic telemetry data, (2) methods to estimate residency and (3) methods to estimate two-dimensional home and occurrence range using geometric or hull-based methods and density-distribution methods, a network-based approach, and three-dimensional methods. We provide examples of some of these were tested using a sample of real data. With this we intend to provide the necessary background for the selection of the method(s) that better fit specific research objectives when using acoustic telemetry.
- Intra- and interspecific associations in two predatory reef fishes at a shallow seamountPublication . Gandra, Miguel; Afonso, Pedro; Fontes, Jorgethe spatial dynamics of marine populations are shaped by habitat availability, environmental variability and individual interactions, particularly when multiple species share limited habitat such as patchy offshore reefs. the yellowmouth barracuda Sphyraena viridensis and the almaco jack Seriola rivoliana are the 2 most abundant bentho-pelagic reef predators in the Azores archipelago (central North Atlantic). They aggregate at shallow offshore seamounts, and largely share diet preferences, but very little is known about how habitat and resources are shared by these predators intra- and inter-specifically. Here we use long-term (over 3 yr) passive acoustic telemetry to investigate the patterns of activity, space use and associative behaviour at an isolated, small shallow seamount. By quantifying fine-scale spatiotemporal overlaps and performing null model randomization tests, we found evidence of non-random associations, mostly between conspecifics of both species, as well as shifts in diel and seasonal patterns of space occupancy. Both species were detected more often during spring, and appear to be more active during daytime, suggesting the absence of fine-scale temporal habitat partitioning. Additionally, we found evidence of size-dependent spatial behaviour in almaco jack, with similarly sized individuals co-occurring more often and larger specimens being more infrequently detected. This study quantitatively assesses individual associations using solely presence-absence data collected through passive acoustic telemetry, showing the potential of this approach in a broader application to a significant number of past and ongoing studies, even if many were not originally designed to study this important aspect of fish ecology.
- Reduced global genetic differentiation of exploited marine fish speciesPublication . Gandra, Miguel; Assis, Jorge; Ramos Martins, Manuel; Abecasis, DavidKnowledge on genetic structure is key to understand species connectivity patterns and to define the spatiotemporal scales over which conservation management plans should be designed and implemented. The distribution of genetic diversity (within and among populations) greatly influences species ability to cope and adapt to environmental changes, ultimately determining their long-term resilience to ecological disturbances. Yet, the drivers shaping connectivity and structure in marine fish populations remain elusive, as are the effects of fishing activities on genetic subdivision. To investigate these questions, we conducted a meta-analysis and compiled genetic differentiation data (FST/ΦST estimates) for more than 170 fish species from over 200 published studies globally distributed. We modeled the effects of multiple life-history traits, distance metrics, and methodological factors on observed population differentiation indices and specifically tested whether any signal arising from different exposure to fishing exploitation could be detected. Although the myriad of variables shaping genetic structure makes it challenging to isolate the influence of single drivers, results showed a significant correlation between commercial importance and genetic structure, with widespread lower population differentiation in commercially exploited species. Moreover, models indicate that variables commonly used as proxy for connectivity, such as larval pelagic duration, might be insufficient, and suggest that deep-sea species may disperse further. Overall, these results contribute to the growing body of knowledge on marine genetic connectivity and suggest a potential effect of commercial fisheries on the homogenization of genetic diversity, highlighting the need for additional research focused on dispersal ecology to ensure long-term sustainability of exploited marine species.
- Assessing data bias in visual surveys from a cetacean monitoring programmePublication . Oliveira-Rodrigues, Cláudia; Correia, Ana M.; Valente, Raul; Gil, Ágatha; Gandra, Miguel; Liberal, Marcos; Rosso, Massimiliano; Pierce, Graham; Sousa-Pinto, IsabelLong-term monitoring datasets are fundamental to understand physical and ecological responses to environmental changes, supporting management and conservation. The data should be reliable, with the sources of bias identified and quantified. CETUS Project is a cetacean monitoring programme in the Eastern North Atlantic, based on visual methods of data collection. This study aims to assess data quality and bias in the CETUS dataset, by 1) applying validation methods, through photographic confirmation of species identification; 2) creating data quality criteria to evaluate the observer's experience; and 3) assessing bias to the number of sightings collected and to the success in species identification. Through photographic validation, the species identification of 10 sightings was corrected and a new species was added to the CETUS dataset. The number of sightings collected was biased by external factors, mostly by sampling effort but also by weather conditions. Ultimately, results highlight the importance of identifying and quantifying data bias, while also yielding guidelines for data collection and processing, relevant for species monitoring programmes based on visual methods.
- A dataset of cetacean occurrences in the Eastern North AtlanticPublication . Correia, Ana M.; Gandra, Miguel; Liberal, Marcos; Valente, Raul; Gil, Ágatha; Rosso, Massimiliano; Pierce, Graham J.; Sousa-Pinto, IsabelThe CETUS project is a cetacean monitoring program that takes advantage of cargo ships to undertake survey routes between Continental Portugal, Macaronesian archipelagos and West Africa. From 2012 to 2017, over 50 volunteers participated in the program, actively surveying more than 124.000 km, mostly beyond national jurisdictions in the high seas, for which little or no previous data existed. In total, the collection comprises 3058 georeferenced transect lines and 8913 positions, which are associated with 2833 cetacean sightings, 362 occurrences of other pelagic megafauna, 5260 estimates of marine traffic and 8887 weather observations. This dataset may provide new insights into the distribution of marine mammals in the Eastern North Atlantic and was published following the OBIS-ENV-DATA format (with the most recent biodiversity data standards at the time of writing). Consequently, it may serve as a model for similar visual line transect data collections yet to be published.
- Depth and temperature preferences of meagre, argyrosomus regius, as revealed by satellite telemetryPublication . Winkler, Alexander; Astrid Bovim, Lily; Macena, Bruno C. L.; Gandra, Miguel; Erzini, Karim; Afonso, Pedro; Abecasis, DavidArgyrosomus regius (commonly referred to as meagre), is one of Europe's largest coastal bony fish species and supports important recreational and commercial fisheries in the Atlantic and Mediterranean coasts. Demand for this species, and more recently for their swim bladders, has led to regional population declines and growing importance as an aquaculture species. Despite intense research in captivity, little is known about the spatial ecology of A. regius's wild population, including basic information such as vertical migrations and depth/temperature preferences. Previous research based on indirect data suggests a seasonal habitat shift from shallow to deeper waters, but this has never been validated through direct high-resolution movement data. In this study, we tagged 13 adult A. regius with pop-up satellite archival tags in the South of Portugal, which successfully returned data from 11 individuals including high-resolution data from six recovered tags (mean, range: 167 days, 28-301 days). We found that adults of this population spend 95.2% of their time between 5 and 75 m depth (mean +/- SD, 30.9m +/- 18.3m) and do not venture beyond 125 m. Across seasons, A. regius move across water temperatures between 13.3 and 24.8 degrees C with a preferred thermal range between 14 and 18 degrees C where they spent 75.4% of their time. The inferential modelling using this electronic data validated previous hypotheses by showing significant differences between a shallower and warmer summer habitat vs. a deeper and cooler winter habitat. Visual investigation of the diel effects on depth preferences suggests subtle changes in depth use between day and night during the warmer months of the year. We speculate that these patterns are in response to the species' behavioural ecology and physiology, reflecting the seasonal changes in water stratification and presence of prey, as well as on the species reproduction, which results in summer spawning aggregations in shallower areas.