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Movements of four adult giant trevally Caranx ignobilis were tracked using passive acoustic telemetry after being released from uShaka Sea World Aquarium in Durban, South Africa, where they had been kept on display for a period of 8 years. All four individuals were detected on a large network of deployed acoustic receivers for a minimum of 3 months to a maximum of over 6 years. Their movements were compared to 43 wild‐caught and tagged C. ignobilis over a similar period and two individuals adopted movement behavior similar to that of their conspecifics, including repeated annual seasonal migrations to a known spawning aggregation site. This study shows that with good animal husbandry, indigenous fish kept in captivity can be released back into the wild and not only survive but adopt natural movement behavior and contribute to future generations of their species. Research highlights: Giant trevally released back into the wild from an aquarium survived for up to 6 years postrelease.Aquarium‐released fish adopted the movement behaviors of their wild conspecifics.Aquarium‐released fish were recorded joining their wild conspecifics at a well‐known spawning aggregation site. [ABSTRACT FROM AUTHOR]

Global shark populations are in serious decline, especially due to overexploitation through fisheries, whose impact is often increased by a lack of proper management regulations and enforcement. South Africa's population of chondrichthyan fauna is one of the most diverse in the world, with high rates of endemic and imperiled elasmobranch species. South Africa has been lauded as a global leader in shark conservation through progressive management legislation, such as the 2013 National Plan of Action for the Conservation and Management of Sharks (NPOA-Sharks I). However, South Africa's shark populations have continued to decline. This study aimed to survey stakeholders' (students, academics, government representatives, conservationists, recreational anglers, commercial fishers, and tourism-related stakeholders) perspectives on the efficacy of NPOA-Sharks I in managing and enforcing fisheries regulations and to advise the 2022 NPOA-Sharks II approach concerning the conservation of South African elasmobranchs. A total of 89 stakeholders participated in an online questionnaire survey launched in 2021. Most stakeholders viewed the NPOA-Sharks I as somewhat appropriate, South Africa's current exploitation of shark stocks as unsustainable and management and enforcement of regulations as inadequate. Commercial fishing and lack of enforcement were ranked as the two most pressing issues facing South Africa's sharks. Similarly, the expert review panel found limited progress (<50%) made in the implementation of the NPOA-Sharks I concerning regulatory tools and sustainable management and called for improved monitoring, surveillance and enforcement of compliance regulations across fisheries as one of the top recommendations for immediate implementation in NPOA-Sharks II. However, the majority of action items under the "Sustainable Management" issue cluster in NPOA-Sharks II suggest a reassessment or reestablishment of existing regulations or the development of new regulatory tools with few specifics provided, reflective of a disconnect between what the lead government agency responsible for the management of South Africa's sharks, the Department of Forestry, Fisheries and the Environment (DFFE), perceives to be effective and what stakeholders experience concerning shark conservation in South Africa. What was perceived by the national management agency as effective concerning shark conservation in South Africa was not necessarily experienced as such by the stakeholders. There is a need for increased collaboration among stakeholders and significant improvements in the practical management of South African fisheries for shark conservation, which is now also suggested in the NPOA-Sharks II. • Stakeholders consider the exploitation of South Africa's sharks unsustainable. • Stakeholders concur that the management of sharks is poor or worse. • Commercial fishing and lack of enforcement are ranked as top threats. • Enforcement is ranked as the most urgent management action. • Stakeholders recognize South Africa's sharks are struggling. [ABSTRACT FROM AUTHOR]

Abstract Marine fishes in the intermittently open East Kleinemonde Estuary, South Africa, were sampled using seine nets over a twenty year period between 1994 and 2014. This dataset was analysed after 11 years (1994–2005), and represented one of the few medium-term studies of fish communities in an intermittently open estuary. A further nine years of sampling (2006–2014) allowed us to revisit the fish community and to gauge if 20 years of data provides more insight into long-term trends in the fish community. The overall species abundance follows a cyclical pattern with two to three years of low abundance and two to three years of high abundance. This pattern broke down in the last five years of the study, with a decline in species richness and consistently low catches of almost all marine species recorded. This may have been as a result of a reduction in the area of submerged macrophytes in the estuary, as well as an increase in the frequency of mouth opening and subsequent decrease in available water area. Graphical abstract Image 1 Highlights • Fish species abundance shows cyclical pattern. • Consistently low catches of all species recorded in last five years of the study. • Low catches may be attributed to habitat loss and a decrease in available water area. • Study shows value of long-term monitoring. [ABSTRACT FROM AUTHOR]

Quantifying the abundance and distribution of fish is fundamental to gaining an understanding of how habitat type, water depth or abiotic conditions influence fish assemblages throughout estuarine systems. Such investigations are inherently difficult because estuaries typically contain a range of habitats across varying depth strata, and data usually consist of replicate samples that cover only a small portion of an entire estuary. We used replicate acoustic-camera (DIDSON) transects along the entire length of a small SouthAfrican estuary to determine the distributions of different size cohorts of fish. Each size cohort was distributed heterogeneously along the estuary, with abundances peaking in discreet sections of the system. By comparing the abundance of fish to the bathymetry, we found correlations between depth and abundance for two of three size classes.Large fish (>401mm)weremore abundant in deep holes (<3m),whereas therewere more small fish (100-250 mm) in shallow (>1.5 m) upper reaches of the estuary. This investigation demonstrated the usefulness of extendedDIDSONtransects to rapidly collect data on the distributional abundance of estuarine fish fromthe estuary mouth to the head, showing that bathymetry of a system may be an important factor in determining these patterns. [ABSTRACT FROM AUTHOR]

Acoustic telemetry was used to assess estuarine area use and movements of an overexploited, endemic fishery species in three South African estuaries; two permanently open systems with contrasting salinity gradients and an intermittently open system. Forty juvenile white steenbras Lithognathus lithognathus (215–379 mm FL) were surgically equipped with acoustic transmitters and tracked for up to 355 days. Tagged fish exhibited high levels of site fidelity and long-term residency within each estuary. Most of their time was spent in the lower reaches of all three estuaries and hypersalinity restricted movements into the upper reaches of the freshwater-deprived estuary. All tagged fish exhibited a distinct diel movement pattern. Most individuals (91%) in the two permanently open estuaries also exhibited a tidal-associated pattern, which comprised mainly small-scale (tens to hundreds of metres) transverse movements between deep channels and shallow banks. Observed behaviour was consistent across a range of estuary sizes, types and physico-chemical conditions. This study has identified critical habitats for juvenile white steenbras across a range of estuarine environments. Estuarine management initiatives need to consider these critical habitats, in order to enhance abundance of juveniles and ultimately recruitment to the marine (adult) population. [ABSTRACT FROM AUTHOR]

Highlights: [•] We examined the effects of passing boats on the abundance of fish within an estuary. [•] A decrease in abundance of mid-sized fish occurred following the passage of boats. [•] Displacement may be attributed to noise, bubbles and the rapidly approaching boat itself. [Copyright &y& Elsevier]

The residency and small-scale movements of early juveniles (<175 mm fork length) of three sparid fish species were examined in the shallow subtidal zone along a 500 m stretch of rocky coastline near Schoenmakerskop (Eastern Cape Province, South Africa). A total of 12 blacktail (Diplodus capensis), 12 zebra (Diplodus hottentotus) and six white musselcracker (Sparodon durbanensis) were tagged using visible implant elastomer (VIE) tags. Underwater observations in four shallow rocky subtidal gullies and adjacent areas were made using snorkelling gear on a total of 37 days spanning 13 field trips over spring low tide periods between January and August 2006. The VIE tagging method was well suited to individually tag small juvenile fish with minimum disturbance. In general, the degree of residency of juveniles in the shallow rocky subtidal zone was species specific and dependent on the size of individuals. Juvenile zebra displayed the highest degree of residency followed by white musselcracker and blacktail, with re-sightings recorded on 53%, 40% and 10% of observation days, respectively. The high degree of residency by early juvenile sparids renders them vulnerable to localized coastal perturbations and climate change. [ABSTRACT FROM AUTHOR]

Urbanization has been identified as a global threat to biodiversity. Human population growth in coastal areas, including estuaries, is expected to increase considerably in coming decades, which will result in a proliferation of infrastructure such as jetties, wharfs and marinas. This infrastructure is often associated with artificial night lighting, yet the implications of these unnatural lighting regimes for the fish fauna in coastal ecosystems are unknown., We conducted novel, night-time surveys of the fish community directly adjacent to an artificial structure using an acoustic camera ( didson). By manipulating the artificial lighting conditions (lighting either 'on' or 'off'), we tested the effects of artificial light on fish abundance and behaviour., Clear differences in the abundance of fish were observed between the two light treatments. The occurrence of large-bodied predators (>500 mm TL) increased when the artificial lights were on. The behaviour of these fish also differed as they attempted to maintain their position within the illuminated area adjacent to the associated anthropogenic structure. The abundance of small shoaling fish also increased when the lights were on., It is possible that the conditions created by artificial lighting benefit piscivores through the concentration of prey and enhanced foraging capabilities in the case of visual predators. This has the potential to create unnatural top-down regulation of fish populations within urban estuarine and coastal waters., Synthesis and applications. As a consequence of a positive phototaxic response, the findings of this study suggest that artificial light often associated with man-made structures has the potential to alter fish communities within urban estuarine ecosystems by creating optimal conditions for predators. Future coastal developments should consider the ecological implications of lighting on aquatic communities. We recommend that lighting be minimized around coastal infrastructure and the use of red lights, which have limited penetration though water, be considered. [ABSTRACT FROM AUTHOR]

Abstract: Over exploitation of fish stocks in coastal areas is a subject of global concern. Increasing numbers of traditional fish traps, recreational fishing effort and unknown extents of illegal gillnetting are blamed for the declining abundance of estuarine-dependent fish species in the Kosi Bay estuarine lake system in KwaZulu-Natal, South Africa. Otoliths from four important fishery species (Lutjanus argentimaculatus, Pomadasys commersonnii, Acanthopagrus vagus, and Rhabdosargus sarba) and water samples collected from throughout the Kosi Bay system were analyzed for trace element constituents and δ 18O values, in an attempt to reconstruct fish movements. The applied microscopic X-ray fluorescence analysis proved valuable in detecting μm-scale spatially resolved Sr/Ca ratio distributions across otolith thin sections. Sr/Ca ratios and δ 18O in otoliths correlated well with ambient water conditions and, thus, enabled us to reconstruct migratory histories of individual fish in the estuarine lake system. The findings are representative of the known biology of these species, although exact spatial and temporal ranges of migrations remain unclear. Interestingly, samples of two species (L. argentimaculatus and R. sarba) did not show any clue of migrations back to sea, which would be necessary for successful spawning. Further laboratory and field investigations with larger sample sizes are necessary to detect fishery impacts on migratory behavior at a population level. [Copyright &y& Elsevier]

Abstract: The natural distribution of early juvenile (<150 mm TL) dusky kob Argyrosomus japonicus (Sciaenidae) along the east coast of South Africa appears to be restricted to the reduced salinity upper reaches of estuaries. This study experimentally tested the effect of salinity on growth indices in an attempt to explain the estuarine distribution of early juvenile A. japonicus. Growth under laboratory conditions was used as an indicator of relative energy expenditure for osmoregulation at salinities 5 (hypoosmotic), 12 (isosmotic) and 35 (hyperosmotic), as energy used for osmoregulation becomes unavailable for growth. Juveniles (81 ± 1.5 mm SL and 9.6 ± 0.5 g) survived and grew at all three salinities over a nine-week period. Contrary to what was hypothesised, growth of juveniles increased with increasing salinity (average weight 35.57 ± 1.50 g, 42.31 ± 2.70 g and 48.86 ± 1.30 g for the 5, 12 and 35 treatments respectively), with specific growth rate of juveniles at the hypoosmotic salinity (2.05 ± 0.15) significantly lower than at isosmotic (2.52 ± 0.09) and hyperosmotic salinities (2.59 ± 0.09). Food conversion ratio was significantly higher at the hypoosmotic (1.30 ± 0.28) than the hyperosmotic salinity (0.94 ± 0.05), but there was no difference between the isosmotic (1.01 ± 0.08) and hyperosmotic salinity. Salinity did not affect condition factor (range: 2.67 ± 0.03–2.75 ± 0.10) or feed intake (range: 2.43 ± 0.17–2.75 ± 0.53). The results, in part, indicated that early juvenile A. japonicus expend more energy at salinities below isosmotic levels and that salinity alone does not explain their natural distribution within estuaries. It is possible that high conductivity in the upper reaches of certain South African estuaries may mitigate the negative effect of reduced salinity on growth and hence the estuarine distribution of early juveniles. [Copyright &y& Elsevier]

Marine predators are vital to the healthy functioning of coastal ecosystems, but to understand their roles, it is necessary to elucidate their movement ecology, particularly in relation to one another. A decade's worth of acoustic telemetry data (2011–2020) from Algoa Bay, South Africa, was investigated to determine how two mesopredatory species (teleosts: dusky kob Argyrosomus japonicus, n = 11, and leervis Lichia amia, n = 16) and two top predatory species (sharks: ragged‐tooth sharks Carcharias taurus, n = 45, and white sharks Carcharodon carcharias, n = 31) used and shared this bay ecosystem. Multi‐annual seasonal fidelity to the bay was exhibited by all species, but differences in residency were observed among species. Similarly, species used space in the bay differently—the teleosts moved less and had movements restricted to the central and western inshore regions of the bay. Conversely, the sharks roamed more, but detections were concentrated in the western part of the bay for C. taurus and in the eastern part of the bay for C. carcharias. Social network analysis showed that species segregated in space and time on a fine scale. However, there was some interaction observed between C. taurus, L. amia, and A. japonicus, but to varying degrees. This is likely because of strong habitat preferences exhibited by each species and predator–prey relationships between these predatory guilds. Results highlight that the sheltered marine Algoa Bay is a resource‐rich environment, supporting multiple predators with different hunting strategies albeit similar prey preferences. Finally, these species are likely afforded some protection by the current Greater Addo Elephant National Park Marine Protected Area in the bay but are vulnerable to fishing pressure when they leave this ecosystem. [ABSTRACT FROM AUTHOR]

Migration is a critical aspect of ocean ecosystems, and understanding this phenomenon answers ecological and management questions. Given the difficulty in tracking ocean animals across large distances, the extent to which different ray species perform long‐distance movements, such as migrations, remains unknown. This study used passive acoustic telemetry to track the movements of endemic diamond Gymnura natalensis and critically endangered duckbill Aetomylaeus bovinus rays along the South African coastline using a collaborative nationwide network of coastal acoustic receivers for up to 7 years. Duckbill rays were detected significantly more frequently than diamond rays, but both species moved between the south and east coasts of South Africa (traveling up to 1167 km). Tagged individuals were detected significantly more often in their tagging locations during summer months but traveled significantly further distances during winter months. Furthermore, movement models fitted to individual duckbill rays' annual net‐squared displacement identified most individual annual movements as migratory. This evidence suggests that both diamond and duckbill rays make eastward winter migrations and return to specific areas along the coastline during the summer months. The exceptions to this were diamond rays tagged on the east coast that were not found to migrate seasonally, which supports previous research that there is intraspecific variability in migrations for ray species. These findings have implications for understanding ray migration not only on a global scale but also locally for spatial management interventions and population delineation. [ABSTRACT FROM AUTHOR]

Abstract: Habitat variability is one of the factors influencing species richness within estuarine systems, and a loss of habitat can result in a restructuring of the estuarine ichthyofaunal assemblage, particularly if these conditions persist over long time periods. The potential effects of the loss of extensive submerged macrophyte beds (Ruppia cirrhosa and Potamogeton pectinatus) on an estuarine fish assemblage were investigated through an analysis of a long-term seine net catch dataset from the temporarily open/closed East Kleinemonde Estuary, South Africa. Catch data for a 12-year period, encompassing six years of macrophyte presence and six years of macrophyte senescence, indicated that the loss of this habitat did not influence species richness but changes in the relative abundance of certain species were evident. A shift in dominance from vegetation-associated species to those associated with sandy environments (e.g. members of the family Mugilidae) was observed. However, species wholly dependent on macrophytes such as the critically endangered estuarine pipefish Syngnathus watermeyeri were only recorded during years when macrophyte beds were present, while vegetation-associated species such as the sparid Rhabdosargus holubi persisted at lower levels of relative abundance. The reduced abundance of all vegetation-associated fish species during years of macrophyte senescence was probably reflective of declining food resources resulting from the loss of macrophyte beds and/or increased vulnerability to predation. Submerged beds of aquatic plants are therefore important habitats within temporarily open/closed estuaries, South Africa’s dominant estuary type. [Copyright &y& Elsevier]