João Pedro Marques

The fatty acid signature and temperature marker FAs of total polar lipids (PLs) and of the two main phospholipid classes, i.e., phosphatidylcholine (PC) and phosphatidylethanolamine (PE), present in the cardiac muscle of wild meagre (Argyrosomus regius) caught in the Tagus estuary (Portugal) were tested as habitat biomarkers to assess whether there were differences associated with the life cycle stage (i.e., juveniles vs. adults). Dried cardiac muscle was extracted using accelerated solvent extraction (ASE), fractionated by solid-phase extraction (SPE) and high-performance thin-layer chromatography (HPTLC), and analyzed by gas chromatography with flame ionization detection (GC-FID). A clear distinction was found between juveniles and adults in terms of cardiac PL fatty acid profile, temperature marker fatty acids, and in the PC/PE ratio. All differences were statistically significant, reflecting differences in thermal adaptation and thus indicating spatial segregation between juveniles and adults within the estuarine environment. Our findings demonstrated a cardiac fatty acid signature indicative of adaptation to distinct habitats and thermal regimes, manifested through alterations in either the PL profile or the restructuring of the PC and PE classes. According to our results, adult individuals stay in a cooler/deep zone and with high influence of the sea within the estuarine systems (mouth of the estuary), and the juveniles in warmer/shallower and less sea-influenced zones.

Fish Aggregating Devices (FADs), traditionally used to attract and concentrate fish, can also serve as effective environmental enrichment tools in reservoirs, particularly in those with homogeneous characteristics and scarce refuge habitat, enhancing structural complexity and promoting recreational fishing opportunities. This study aimed to evaluate patterns in the use of prototype fish aggregation devices (FADs) in small size reservoirs. It was conducted at the Nascentes Reservoir (Crato), a small Mediterranean reservoir (ca. 10 ha) located in southern Portugal. These FADs were installed to enhance refuge habitat for fish species of interest to recreational fisheries, particularly largemouth bass (Micropterus salmoides Lacepède, 1802), thereby promoting the occurrence of trophy specimens. Two types of FADs were deployed and tested: (1) bank FADs (TREES), used in shallow waters near the margins; and (2) pelagic FADs (DAPs), suspended in the water column in deeper areas at the center of the reservoir. To monitor movement patterns and habitat use, an acoustic telemetry receiver array was deployed with a design to secure a three-dimensional fine-scale positioning with high accuracy. A total of 20 largemouth bass were tagged with acoustic transmitters equipped with pressure (i.e., depth) sensors. A before–after approach was used with 10 fish tracked before FAD deployment and 10 after. Results of fish behavior analysis provide strong evidence of fish using DAPs, but not TREES. In the presence of FADs, fish reduced their home ranges and movement amplitudes, becoming closely associated with these artificial habitats. Several environmental predictors explained fish behavior in the presence of artificial refuges, namely, diel period, moonlight intensity, and fish depth. The findings of this study are expected to contribute to the development of guidelines for refuge habitat enhancement in small- to medium-sized Mediterranean reservoirs, thereby increasing their recreational fishing attractiveness.

The Iberian barbel (Luciobarbus bocagei Steindachner, 1864) is a potamodromous species that displays migratory movements, with adults moving upstream during spring to spawn, followed by downstream migration in autumn by both adults and juveniles to feed and inhabit more productive river stretches. Increasing river fragmentation due to dam construction and operation causes a loss of connectivity and suitable habitat, which can affect this natural behaviour. In a tributary of River Douro, River Tua, a 108 m high dam, was recently built (i.e., Foz Tua dam in 2017) at only 1.1 km from the river mouth, leaving the upstream spawning area inaccessible. To evaluate the species behavioural response to this impact, a passive acoustic telemetry array was deployed in the study area, and between 2018 and 2023, 120 tagged fish had their movements tracked. The results showed two different behavioural profiles in the same population with migratory (42.5%) and resident (54.0%) individuals. During this period, a specific experimental study was developed to evaluate the response of a subset of 90 fish, captured upstream of the Foz Tua dam and translocated to an alternative downstream Douro tributary (River Pinhão, ~20 km downstream from River Tua). From these, 66.7% remained at the release site, whilst 23.3% returned to the river of origin, i.e., River Tua. From the returned fraction, 28.6% of the tagged fish maintained this migratory behaviour between both rivers in the following years. Generalized Additive Models were used for each of the two behavioural profiles observed in this study, to identify which environmental variables were associated with the presence of the tagged barbels downstream the Foz Tua dam. Ecological flow, temperature and day-period were some of the predictors explaining the use of this river stretch downstream of Foz Tua dam. This study substantially updates the available information regarding this species’ movement patterns at large spatial and temporal scales, contributing to enhancement of management and conservation programs for potamodromous species, in highly impounded and fragmented rivers.

We used acoustic telemetry to investigate the nursery habitat use of 33 juvenile meagre Argyrosomus regius (mean size = 581 ± 105.1 mm), recording more than 60,000 detections in the Tagus estuary, located in the North-Eastern Atlantic. All individuals used the nursery area from spring to autumn, and a small number (22.2%) remained in the Tagus estuary during winter. Daily movements averaged 6.2 ± 1.9 km, with maximum daily distances reaching 41.2 ± 17.3 km. Peak movement activity was observed in July-October (average distance = 367.3 ± 240.3 km), and predominantly during the night. Furthermore, larger sized individuals returned to the Tagus estuary in subsequent years, typically using this habitat from May to October for an average of 108.5 ± 43.0 days. Spatial analyses indicated that the lower and middle sections of the Tagus estuary serve as important nursery habitats year-round, whereas the upper estuary functions as a nursery primarily from March through June. Network movement analyses highlighted that specific areas in the middle and lower reaches exhibit higher movement activity. Generalized additive modelling indicated that the occurrence of juvenile meagre in the Tagus estuary was significantly influenced by temporal and environmental variables, including day of the year, salinity, dissolved oxygen, and temperature, measured both in the estuary and in the adjacent coastal area. These findings enhance our understanding of the habitat use in estuarine nursery areas and emphasise the importance of incorporating targeted fisheries management strategies in nursery areas to promote the sustainability of this ecologically and economically important fish.

Aim: The urgency for remote, reliable and scalable biodiversity monitoring amidst mounting human pressures on ecosystems has sparked worldwide interest in Passive Acoustic Monitoring (PAM), which can track life underwater and on land. However, we lack a unified methodology to report this sampling effort and a comprehensive overview of PAM coverage to gauge its potential as a global research and monitoring tool. To address this gap, we created the Worldwide Soundscapes project, a collaborative network and growing database comprising metadata from 416 datasets across all realms (terrestrial, marine, freshwater and subterranean).Location: Worldwide, 12,343 sites, all ecosystem types.Time Period: 1991 to present.Major Taxa Studied: All soniferous taxa.Methods: We synthesise sampling coverage across spatial, temporal and ecological scales using metadata describing sampling locations, deployment schedules, focal taxa and audio recording parameters. We explore global trends in biological, anthropogenic and geophysical sounds based on 168 selected recordings from 12 ecosystems across all realms.Results: Terrestrial sampling is spatially denser (46 sites per million square kilometre—Mkm²) than aquatic sampling (0.3 and 1.8 sites/Mkm² in oceans and fresh water) with only two subterranean datasets. Although diel and lunar cycles are well sampled across realms, only marine datasets (55%) comprehensively sample all seasons. Across the 12 ecosystems selected for exploring global acoustic trends, biological sounds showed contrasting diel patterns across ecosystems, declined with distance from the Equator, and were negatively correlated with anthropogenic sounds.Main Conclusions: PAM can inform macroecological studies as well as global conservation and phenology syntheses, but representation can be improved by expanding terrestrial taxonomic scope, sampling coverage in the high seas and subterranean ecosystems, and spatio‐temporal replication in freshwater habitats. Overall, this worldwide PAM network holds promise to support cross‐realm biodiversity research and monitoring efforts.

The meagre Argyrosomus regius, one of the largest sciaenidae in the world, is a valuable resource for fisheries and aquaculture. Despite its socioeconomic relevance, knowledge about population dynamics and wild stocks is still scarce, and conservation risks are associated with overexploitation. Two genetic distinct groups, one in the North Atlantic Ocean and one in the eastern Mediterranean Sea, were identified by previous studies. However, little is known about the genetic structure of the Atlantic group, where four important spawning areas have been identified. To assess if each spawning area is an independent breeding unit, the genetic diversity, populational structure, and demographic history of A. regius along the North–East and Eastern Central Atlantic coast were analyzed, using 15 microsatellite loci. Results corroborate the hypothesis tested, suggesting four genetic groups: a first group encompassing individuals from the Gironde spawning area, a second group encompassing individuals from the Tagus spawning area, a third group corresponding to individuals captured in the Algarve region, and a forth group gathering individuals from Morocco and Mauritania. This study reveals the need for specific fisheries management plans considering genetic structure information, and highlights the need for international cooperation.

No-take areas are key instruments to promote the effectiveness of Marine Protected Areas (MPAs), particularly concerning the protection of endangered species such as the dusky grouper (Epinephelus marginatus). However, despite the establishment of no-take areas and the prohibition of catching this species in a southwestern Portuguese MPA (SACVMP—‘Sudoeste Alentejano’ and ‘Costa Vicentina’ Marine Park) since 2011, there is still no evidence of population recovery. By using acoustic biotelemetry, this work aimed to evaluate the feasibility of restocking hatchery-reared adult dusky groupers in two no-take areas within the SACVMP. In 2019 and 2021, thirty groupers were tagged with acoustic transmitters and the site attachment and movements of the groupers were assessed in the releasing sites (no-take areas). None of the tagged fish settled down in either of the areas, leaving the no-take areas mainly at dusk and night. Some individuals displayed extended movements of more than a hundred kilometers along the Portuguese coast which was rarely reported for this species. At least in some coastal stretches, those movements were performed close to the shore, which may evidence the importance of coastal MPAs to protect and promote the connectivity of species more associated with rocky reef habitats. Following studies should focus on the conditions that promote site attachment and fidelity by hatchery-reared dusky groupers so that future large-scale restocking programs can be successful in MPAs with appropriate habitats.

Marine Protected Areas (MPAs) have played an important role in the protection of endangered species such as the dusky grouper (Epinephelus marginatus), and the no-take areas have been particularly crucial for this purpose. Yet, despite the establishment of no-take areas and the legislation banning dusky groupers’ catches since 2011 in a southwestern Portuguese MPA (SACVMP—‘Sudoeste Alentejano’ and ‘Costa Vicentina’ Marine Park), there is still no evidence of this population’s recovery. In the face of this, the present work aimed to monitor the experimental hatchery-reared adult dusky groupers’ restocking of two no-take areas of SACVMP with acoustic biotelemetry. In 2019 and 2021, thirty groupers tagged with acoustic transmitters were released in two no-take areas, and the site attachment and their movements were assessed. None of the tagged fish set residency in either of the releasing areas, mostly leaving there at dusk and night. A rarely reported event for this species was also observed, as some individuals moved for more than a hundred kilometers along the Portuguese coast. At least some of those ranging movements were performed close to the rocky shore, which may point out the importance of coastal MPAs in promoting the connectivity of fish species associated with rocky reef habitats. Future studies must focus on the conditions that promote the site attachment and the site fidelity of released hatchery-reared dusky groupers so that large-scale restocking programs can be successfully implemented in MPAs with appropriate habitats.

The meagre is among the largest Sciaenidae in the world (max: 230 cm, 103 kg), with a wide distribution range encompassing the NE and CE Atlantic Ocean and the Mediterranean Sea. The life cycle in Atlantic waters includes migratory movements from feeding and overwintering areas at sea to spawning and nursery areas in estuaries and coastal waters. However, significant spawning aggregations are only observed in five locations, among which is the Tagus estuary (Portugal). The meagre fishery that takes place within the Tagus estuary is significant, accounting for approximately two-thirds of Portuguese meagre catches. Despite its economic relevance, the meagre movements in that region remain largely unknown. The existence of a target fishery inside the estuary alongside a lack of routine biological data collection targeting the species and incipient fisheries control in the area, highlight an urgency to adopt innovative methodologies to unravel meagre migrations and its use of critical areas. We present the first insights of movement patterns and habitat use in the Tagus estuary using acoustic biotelemetry data collected between 2019 and 2021. The acoustic receiver array obtained a total of 142.183 registers from a total of 34 individuals tagged. From the tagged specimens, 33% revisited the Tagus estuary in subsequent years at least once, during the spring and summer, and 49% remained in the Tagus at least until autumn. Further analysis was conducted with juveniles tracked over 3 years to identify critical nursery areas using dynamic Brownian bridge movement models (utilization distribution estimations). The effects of abiotic conditions on the meagre behaviour were assessed using in situ sensor data (e.g., temperature and salinity) and other environmental predictors (e.g., photoperiod and tide cycle) and an explanatory model was developed that helps to understand the use of the Tagus estuary by juveniles. The information collected will be discussed in light of possible applications to promote sustainable management of meagre fisheries in the Tagus estuary and adjacent coastal areas.

The meagre Argyrosomus regius (Asso, 1801) is a marine migratory species with a wide distribution range encompassing the north-eastern and central-eastern Atlantic Ocean, the Mediterranean Sea, and the western Black Sea. A. regius is one of the largest overexploited sciaenids, being a valuable resource for aquaculture and fisheries along its distribution range. The Iberian Peninsula is considered an intermediate area between two genetically distinct groups of A. regius populations, one in the north-eastern Atlantic Ocean and one in the eastern Mediterranean Sea. The current knowledge on the population dynamics and distribution of this species has been derived from commercial and recreational fishery catches; therefore, little is known about the importance of the Iberian Peninsula for the species’ management and conservation. The aim of this study is to evaluate the A. regius population genetic structure along the Portuguese coast taking into consideration the north-eastern Atlantic region. To achieve this goal, the genetic diversity, differentiation, populational structure and demographic history of A. regius populations along the Atlantic coast were analyzed using 15 microsatellite loci. The detected populational structure indicates that A. regius species in Portugal are divided into two distinct stocks, one across the Portuguese western coast, possibly related to the Tagus spawning and nursery area, and another one on the southern coast. This study reveals the need for A. regius-specific fishery management plans in Portugal and underlines the importance of considering the genetic structure of A. regius populations when delineating such management plans.