Search Results (8)

This study aims to clarify the influence of water flow on the behavior of the large yellow croaker (Larimichthys crocea). Although L. crocea is a key species in marine cage aquaculture, and the industry is increasingly adopting large-scale sea cages, the behavioral adaptations of this species under such conditions remain insufficiently characterized. To solve this problem, the study implemented an ultrasonic biotelemetry system to monitor the in situ swimming behavior of L. crocea across varying current velocities and tidal phases. The results indicated that the tagged fish predominantly occupied water depths of 1 to 2.6 m, with no observable circular swimming behavior along the cage periphery. Additionally, the spatial distribution of L. crocea within the large-scale cage seemed to correlate with the direction of the current. Furthermore, both the frequency of appearance and swimming speed of L. crocea were higher in the center of the cage compared to the peripheral regions during flood and ebb tides, whereas the opposite trend was observed during slack water. This study provides novel insights into the behavioral ecology of L. crocea in large-scale aquaculture systems. Full article

Recent technological advances in marine biotelemetry have demonstrated that marine fish species perform activity–rest rhythms that have relevant ecological and evolutionary consequences. The main objective of the present report is to study the circadian rhythm of activity–rest of the pearly razorfish, Xyrichtys novacula in its own habitat, before and during the reproduction season using a novel biotelemetry system. This fish species is a small-bodied marine species that inhabits most shallow soft habitats of temperate areas and has a high interest for commercial and recreational fisheries. The activity of free-living fish was monitored by means of high-resolution acoustic tracking of the motor activity of the fish in one-minute intervals. The obtained data allowed the definition of the circadian rhythm of activity–rest in terms of classical non-parametric values: interdaily stability (IS), intradaily variability (IV), relative amplitude (RA), average activity during the most-active period of consecutive 10 h (M10), and average activity during the least-active period of consecutive 5 h (L5). We observed a well-marked rhythm, with little fragmentation and good synchrony with the environmental cycle of light–darkness, regardless of sex and the period studied. However, the rhythm was found to be slightly more desynchronized and fragmented during reproduction because of variations in the photoperiod. In addition, we found that the activity of the males was much higher than that of the females (p < 0.001), probably due to the peculiar behavior of the males in defending the harems they lead. Finally, the time at which activity began in males was slightly earlier than it was in females (p < 0.001), presumably due to the same fact, as differences in activity or for the individual heterogeneity of this species in the time of awakening are considered to be an independent axis of the fish’s personality. Our work is novel, as it is one of the first studies of activity–rest rhythm using classical circadian-related descriptors in free-living marine fish using locomotory data facilitated by novel technological approaches. Full article

Passive acoustic monitoring is increasingly employed to monitor whales, their population size, habitat usage, and behaviour. However, in the case of the eastern Indian Ocean pygmy blue whale (EIOPB whale), its applicability is limited by our lack of understanding of the behavioural context of sound production. This study explored the context of singing behaviour using a 7.6-day biotelemetry dataset from a single EIOPB whale moving north from 31.5° S to 28.5° S along the Western Australian coast and a simultaneously collected, but separate, acoustic recording. Diving behaviour was classified using an automated classification schema. Singing was identified in the depth, pitch, and fluking time series of the dive profile. The EIOPB whale sang profusely as it migrated, spending more time singing during the day (76.8%) than at night (64.9%), and most during twilight periods (83.3%). The EIOPB whale almost exclusively produced the three-unit (P3) song while milling. It sang the two-unit (P2) song in similar proportions to the P3 song while travelling, except at night when P3 was sung 2.7 times more than P2. A correlation between singing depth, migration duration, and water temperature provides a biological basis to explain depth preferences for sound production, which may contribute to the cause of intra- and inter-annual sound frequency trends. Full article

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. Full article

The trout Salmo trutta L. is an iconic fish species very well studied across most of its range. However, there is a lack of information about the biology and ecology of S. trutta populations from southern European rivers, which coincide with the southern limit of its global distribution. This study aims to analyse the movement patterns and habitat use of S. trutta in the Mondego River basin, Central Portugal, and relate them with the environmental factors to which the species is exposed. Biotelemetry represents an important tool to obtain temporal and spatial specific details about the behaviour of target species and, in this work, we used a set of complementary techniques, namely acoustics, radio and PIT telemetry. A total of 114 trout specimens were tagged with PIT-tags, to be identified in future recaptures or detected at an antenna installed at Coimbra dam fish pass. From these, 18 were also tagged with Dual Mode transmitters, that include radio and acoustic telemetry signals, allowing to track the species’ movements from the estuary to the upstream freshwater sections. Results show the existence of a migratory peak between November and January that coincides with the reproduction season, while reinforcing the importance of Alva River to spawning S. trutta, one of the main tributaries in the study area. River fragmentation in the study area, particularly in the tributaries, is still limiting the vital area of the tracked individuals, although recent restoration actions provided easier access to some important areas in this river for distinct trout life-stages. This study aims to improve the knowledge of southern European trout populations, contributing to enhancing efforts for restoring and managing these populations inhabiting areas under severe climate change effects. Full article

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. Full article

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. Full article

The European catfish (Silurus glanis) is a non-native species with invasive character to Iberian freshwaters. Being the largest fish species in those invaded water bodies, with high fecundity rates, a large life expectancy and an extraordinary predatory potential, S. glanis has all the indicators that it could be exerting a dangerous pressure on native fish communities. Albeit there are some studies regarding the activity and depth use of this catfish, many of them are restricted to its native range and do not describe the circadian and annual behaviours in detail. Moreover, no studies have compared the differences in habitat use and movement ranges between adults and juveniles in a recently invaded territory. To fill these knowledge gaps, this study resorts to acoustic biotelemetry to track 25 fish (10 adults and 15 juveniles) in a Tagus river reservoir, the Belver dam, through an array of fixed acoustic receivers. The fish were internally tagged with acoustic transmitters, which, in the case of the adults, including a 3D-accelerometer and pressure sensors that allow obtaining information on activity and depth use for over a year. The results show that S. glanis is active throughout the year but with higher activity levels in summer and minimal in autumn, and with a crepuscular and nocturnal increase in activity. This species occupies shallower depths in spring/summer, while in autumn/winter roams at relatively deeper waters. Circadian vertical movement patterns were identified; however, they vary seasonally and have some individual variability. The areas used by the adults are larger than the juveniles’ and increase in warmer months. Adult preferences in the use of specific areas across the year and a possible migration to a spawning site were identified. Such findings will support the development of more effective control measures, for instance, by providing information on how to allocate the fishing efforts in space and time to maximize the efficiency of mass removal actions of this invasive fish. Full article