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Intra-specific variability in movement behaviour occurs in all major taxonomic groups. Despite its common occurrence and ecological consequences, individual variability is often overlooked. As a result, there is a persistent gap in knowledge about drivers of intra-specific variability in movement and its role in fulfilling life history requirements. We apply a context-focused approach to bull sharks (Carcharhinus leucas), a highly mobile marine predator, incorporating intra-specific variability to understand how variable movement patterns arise and how they might be altered under future change scenarios. Spatial analysis of sharks, acoustically tagged both at their distributional limit and the centre of distribution in southern Africa, was combined with spatial analysis of acoustically tagged teleost prey and remote-sensing of environmental variables. The objective was to test the hypothesis that varying resource availability and magnitude of seasonal environmental change in different locations interact to produce variable yet predictable movement behaviours across a species’ distribution. Sharks from both locations showed high seasonal overlap with predictable prey aggregations. Patterns were variable in the centre of distribution, where residency, small- and large-scale movements were all recorded. In contrast, all animals from the distributional limit performed ‘leap-frog migrations’, making long-distance migrations bypassing conspecifics in the centre of distribution. By combining multiple variables related to life history requirements for animals in different environments we identified combinations of key drivers that explain the occurrence of differing movement behaviours across different contexts and delineated the effects of environmental factors and prey dynamics on predator movement. Comparisons with other taxa show striking similarities in patterns of intra-specific variability across terrestrial and marine species, suggesting common drivers. Animal movement, Context, Intra-specific variability, Resource availability, Bull sharks, Birds, Marine predators, Environmental change Context drives movement patterns in a mobile marine predator

20 pages, 3 tables, 5 figures.-- Samantha Andrzejaczek ... et al.-- Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC), Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra- and interspecific variability in vertical movement patterns. Substantial vertical overlap was observed for many epipelagic elasmobranchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps toward incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasizing the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements, Data analysis was funded by the Bertarelli Foundation through the Marine Science program through grants to D.J.C., B.A.B., and S.A. D.J.C. is also funded through Research England, UK. S.A. and B.A.B. thank the Moore Foundation and the Packard Foundation. F.G.-M. thanks the Instituto Politecnico Nacional for fellowships (COFAA, EDI). S.B.W. thanks funding from the Darwin Initiative (DPLUS046). A.D.M.D. acknowledges funding from the Research and Conservation Budget at Georgia Aquarium, including philanthropic gifts from several anonymous donors. K.F. acknowledges funding from the Rolex Awards for Enterprise and the Whitley Fund for Nature

Defining the home range of vulnerable species is critical for designing effective spatial management strategies. However, animal home ranges often change with ontogeny, and quantifying the associated temporal and spatial changes is particularly challenging for mobile marine species. Here, we investigated how the space use of a top predatory reef-associated fish (giant trevallyCaranx ignobilis) scales with body size. Fish were tagged with acoustic transmitters and passively tracked for >3 yr at a tropical island and atoll in the Republic of Seychelles. A sheltered atoll environment was critical for juvenile fish (100 cm FL) adult fish appeared to favour shallow coral reefs and associated reef drop offs whilst sharing a similar core home range location. Large adult fish utilized a greater diversity of habitat types and had significantly (p < 0.05) greater annual dispersal distances (mean = 35.29 km, max = 91.32 km) than small adults (mean = 13.72 km, max = 21.55 km). Additionally, the home range of large adults (mean = 209.74 km2) was significantly (p < 0.05) larger than that of juveniles (mean = 38.73 km2) and small adults (77.32 km2) and there was a significant (p = 0.02) relationship between fish length and home range size. Furthermore, tagged fish took up to 34 mo (mean = 18.54 mo) to utilize the full extent of their home range. The habitat shift and expansion in home range size throughout ontogeny should be taken into account when designing effective spatial management plans forC. ignobilis.

Information on the movement ecology of endangered species is critical for the implementation of effective conservation measures. This study made use of a long-term dart tagging dataset to reveal the movement patterns and growth rates of two size classes of the Critically Endangered whitespotted wedgefish Rhynchobatus djiddensis within its southern African distribution, which can have important implications for fisheries management. A total of 4 768 individuals were tagged with 340 recaptures recorded, ranging from 1 to 2 639 days (7.2 years) at liberty. Most of the tag releases and recaptures occurred within the KwaZulu-Natal central region in South Africa, with catches increasing significantly during summer (October to March). Most recaptures (43%) were recorded within 5 km of the tagging (release) site. Tagged adults recorded significantly greater distances moved than juveniles (p 0.30). A Francis growth model showed that smaller individuals had a substantially faster growth rate (198.69 [SE 21.75] mm year−1) compared with larger individuals (57.41 [SE 27.83] mm year−1) confirming that the species is relatively slow-growing. Ultimately, this study identified important knowledge gaps in the broadscale movement patterns of R. djiddensis and provided new information on the growth rate of this Critically Endangered species. Filling in these knowledge gaps will aid in conservation measures for two important size classes of the R. djiddensis population as the species faces increasing targeted fishing pressure.

Information on the spatial ecology of batoids is lacking despite the need for this information for effective management and conservation of this vulnerable faunal group. We used acoustic telemetry to monitor the presence of dasyatids (Pastinachus ater, Urogymnus granulatus, and U. asperrimus) from March 2014 to November 2017 within and around the isolated St. Joseph Atoll, Seychelles. Results highlighted residency (median residency index = 0.75 and 0.57 for P. ater and U. granulatus) over periods of months to years for both juveniles and adults. Individuals displayed highly restricted movements; most detections occurred within 1 km of tagging locations, and movement networks were small and fragmented. However, juveniles increased their range of movements with size before dispersing to various locations on the Amirantes Bank. Within the atoll, resident adults and juveniles segregated ontogenetically by habitat; adults were more reliant on the deeper lagoon, while juveniles were largely restricted to the shallow sand flats, likely in an effort to avoid predators. Conversely, no inter-specific space partitioning was identified. This study provides preliminary evidence that this atoll is a dasyatid nursery; however, comparative research at other atolls is required to understand the role that atolls may play as batoid nurseries. This study was performed in the South West Indian Ocean, an understudied fisheries conservation hotspot where biodiversity is high but management effectiveness is low. The identification of a dasyatid refuge in this region highlights that the current marine protected area designation will likely provide conservation benefits for the dasyatid populations across the entire Amirantes Bank.

The red steenbras Petrus rupestris is endemic to South Africa, occurring from False Bay in the Western Cape Province to St Lucia in the province of KwaZulu-Natal. This species, the largest member o...

Top predators have substantial downstream effects on the structure, function, and resilience of ecosystems. The influence of top predators on an ecosystem can vary if they occur within multiple habitat types and have a wide niche breadth due to spatiotemporal changes in diet. We examined spatial patterns in trophic position and niche width for an economically important reef-associated fishery species, the giant trevally Caranx ignobilis. We sampled 4 localities in the western Indian Ocean representing different habitats: coral atolls, coastal reefs, and granitic islands. We analyzed isotopic ratios of carbon (13C/12C) and nitrogen (15N/14N), and performed compound-specific amino acid stable isotope analysis (AA-CSIA) to control for baseline nitrogen variation. Our analysis of 12 juveniles and 43 adults revealed wide variation in trophic niche breadth between sampling sites and an offshore to coastal gradient in carbon that drove niche distinctiveness between localities. We observed niche width patterns suggestive of ontogenetic changes in diet and habitat utilization and larger niche sizes at the oceanic island sites than the coastal site. Trophic position estimates ranged from 3.5-5, expanding the trophic range of C. ignobilis relative to previous studies using AA-CSIA and placing it at the equivalent trophic level as many predatory sharks. Our study corroborates prior evidence that C. ignobilis is an important apex predator in reef and island ecosystems. Additionally, we show how evaluating spatiotemporal components of trophic ecology of marine predators is critical for characterizing their functional role and ecosystem influence, allowing for targeted conservation efforts.

Acoustic telemetry (AT) is a rapidly evolving technique used to track the movements of aquatic animals. As the capacity of AT research expands it is important to optimize its relevance to management while still pursuing key ecological questions. A global review of AT literature revealed region-specific research priorities underscoring the breadth of how AT is applied, but collectively demonstrated a lack of management-driven objectives, particularly relating to fisheries, climate change, and protection of species. In addition to the need for more research with direct pertinence to management, AT research should prioritize ongoing efforts to create collaborative opportunities, establish long-term and ecosystem-based monitoring, and utilize technological advancements to bolster aquatic policy and ecological understanding worldwide.

The pyjama shark Poroderma africanum (family Scyliorhinidae) is endemic to coastal waters of South Africa but its population characteristics are poorly known. This study aims to estimate baseline d...

BackgroundBonefishes are cryptic species indiscriminately targeted by subsistence and recreational fisheries worldwide. The roundjaw bonefish, Albula glossodonta is the most widespread bonefish species in the Indo-Pacific and is listed as vulnerable to extinction by the IUCN’s Red List due to anthropogenic activities. Whole-genome datasets allow for improved population and species delimitation, which – prior to this study – were lacking for Albula species.ResultsWe generated a high-quality genome assembly of an A. glossodonta individual from Hawai‘i, USA. The assembled contigs had an NG50 of 4.75 Mbp and a maximum length of 28.2 Mbp. Scaffolding yielded an NG50 of 14.49 Mbp, with the longest scaffold reaching 42.29 Mbp. Half the genome was contained in 20 scaffolds. The genome was annotated with 28.3 K protein-coding genes. We then analyzed 66 A. glossodonta individuals and 38,355 SNP loci to evaluate population genetic connectivity between six atolls in Seychelles and Mauritius in the Western Indian Ocean. We observed genetic homogeneity between atolls in Seychelles and evidence of reduced gene flow between Seychelles and Mauritius. The South Equatorial Current could be one mechanism limiting gene flow of A. glossodonta populations between Seychelles and Mauritius.ConclusionsQuantifying the spatial population structure of widespread fishery species such as bonefishes is necessary for effective transboundary management and conservation. This population genomic dataset mapped to a high-quality genome assembly allowed us to discern shallow population structure in a widespread species in the Western Indian Ocean. The genome assembly will be useful for addressing the taxonomic uncertainties of bonefishes globally.

Marine protected areas (MPAs) can provide distinct conservation benefits for threatened species, particularly in regions where there is a lack of population assessments. The St. Joseph Atoll, Seychelles, has been under consideration for MPA designation due to the presence of multiple threatened and important species. This study aimed to assess the nursery role of this isolated ecosystem for Vulnerable (IUCN) porcupine rays Urogymnus asperrimus. Twenty porcupine rays were tagged with VEMCO transmitters and their movements passively monitored for a 2.5-year period using an array of 88 acoustic receivers. The majority (71%) of porcupine rays displayed medium (RI: 0.34–0.66) to high (RI: 0.67–1) levels of residency and 82% of individuals were detected in the atoll for periods close to or exceeding one year. Horizontal movements were limited as small home ranges and activity spaces were identified (mean of 0.65km2 and 4.35km2 respectively). General linear mixed models highlighted that home range size increased with disc-width and that there was dispersal from the atoll over time. These results have implications for the proposed marine protected area at the St. Joseph Atoll and suggests that protecting this habitat will provide strong conservation benefits for this poorly understood species.

Tourism generated through bonefish (Albula spp.) fishing contributes to the economies of many isolated tropical islands and atolls. However, little research has been conducted on bonefish in the Indian Ocean. This study aimed to contribute to the understanding of bonefish ecology in the Indian Ocean by quantifying the spatial and temporal movements of Albula glossodonta at a near-pristine and predator-rich atoll in the Seychelles; however, to achieve this, an analysis to identify the occurrence of possible post-release predation bias was first necessary. An acoustic telemetry study was initiated at the remote St. Joseph Atoll, within an array of 88 automated data-logging acoustic receivers. Thirty bonefish were surgically implanted with Vemco V13 acoustic transmitters and tracked for one year. Only 10% of the tagged bonefish were detected for longer than two weeks. A comparison of the final 100 h of movement data from fish detected for less than two weeks to the movement data of the fish detected for longer periods revealed distinct differences in area use and significant differences in the average daily distance moved, speed of movement and frequency of detections. This suggested that mortality in the form of post-release predation was at least 43% of tagged fish. The three surviving bonefish were tracked for 210 to 367 days. These individuals remained in the atoll and showed high use of the marginal habitats between the shallow sand flats and the lagoon. A generalised linear mixed model identified that water temperature, diel cycle and tide were significant predictors of bonefish presence in the lagoon. The high post-release mortality highlights that catch-and-release is likely not as benign as previously believed and management and policy should be adjusted accordingly.

This study made use of data from three long-term fish tagging projects along the South African coastline to investigate the movement behaviour of the endemic black musselcracker Cymatoceps nasutus (Sparidae). From 1984 to 2016, a total of 3 430 C. nasutus (178–980 mm fork length) were tagged (with small plastic dart tags) throughout the species’ distributional range, with an overall reported recapture rate of 7.2%. Recaptured individuals displayed high levels of residency, moving an average of 14.8 km, with time-at-liberty ranging from 0 to 6 809 days. The majority of recaptures (84.6%) were made within 1 km of the tagging sites; however, some large-scale movements, of up to 528 km, were recorded. Although C. nasutus individuals moving greater distances were characterised by greater mean sizes (mm fork length) at time of recapture, the distances moved by juveniles were not significantly different from those of adults (p > 0.05). Low levels of connectivity among coastal regions were therefore expected due to the high degree of residency displayed by this species. Combining traditional management approaches together with a well-designed network of no-take marine protected areas is likely to be the most effective way to protect this vulnerable species. A lack of data on the movements of adults remains a challenge, but this could be overcome by tracking large individuals tagged with long-life acoustic transmitters. Keywords: dart tags, fisheries management, linefish, marine protected area, poenskop, resident species, site fidelity

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.

Area management in the form of no-take marine protected areas (MPAs) has been criticised as a fisheries management tool because of its limited capacity to provide short-term benefits to local fisheries. This study used data from a long-term fish monitoring and tagging project to assess whether catch-and-release (C&R) shore angling could be compatible with the management objectives of a large, multiple-use, zoned MPA in South Africa. Tag-recapture rates, trends in relative abundance and mean size of target species, sub-lethal effects and other potential environmental impacts suggested that C&R research angling, using best practise fish handling techniques, did not have an overall negative impact on protected fish populations. While positive from a scientific monitoring perspective, more sensitive species did show evidence of increased post-release mortality that would be exacerbated by higher intensity C&R angling conducted by members of the angling public. It is thus concluded that C&R shore angling by members of the angling public is not compatible with MPAs zoned for no-take. However, because C&R angling does have substantially lower negative impacts compared to recreational harvest fisheries, areas zoned for C&R offer good potential as buffer areas adjacent to no-take areas or as stand-alone areas where fish conservation can be improved. This concept is proposed for the improved conservation of surf-zone angling fish species within the iSimangaliso Wetland Park and further afield.

Connectivity — movements of animals between and among numerous habitats — and the factors (rhythmic cycles and environmental variables) influencing connectivity of juvenile Lichia amia (Teleostei: Carangidae) were assessed in complementary acoustic telemetry studies in two geographically separated estuaries (620 km apart) in South Africa. The studies were conducted within a nationwide array of acoustic receivers moored in estuaries and coastal waters. Tagged fish in both the Kowie (n = 21) and Goukou (n = 17) estuaries displayed high levels of multiple habitat connectivity, with 81% and 76% visiting nearby marine and estuarine environments, respectively. The presence of tagged L. amia within the tagging estuaries was significantly influenced by river and sea temperature (Kowie) and river inflow and moon phase (Goukou). Tidal phase, time of day, and season were found to significantly influence marine excursions undertaken by Kowie- and Goukou-tagged fish. Our study provides an assessment of connectivity among multiple estuarine, port, and marine habitats, relating those movements to rhythmic cycles and environmental variables, and highlights the benefits of tracking animals using an extensive acoustic receiver array that spans multiple habitats.

The estuarine pipefish, Syngnathus watermeyeri, is one of the rarest animals in Africa and occurs in only two South African estuaries. The species was declared provisionally extinct in 1994, but was later rediscovered and is currently listed by the IUCN as Critically Endangered. A conservation programme was launched in 2017, with the re-introduction of captive-bred individuals into estuaries where this species was recorded historically was the main aims. Successful captive breeding requires knowledge of the species9 dietary requirements. In the present study, we used metabarcoding of faecal DNA to identify prey species consumed by wild-captured S. watermeyeri from one of the two surviving populations. We compared the diet of the estuarine pipefish with that of the longsnout pipefish, S. temminckii, in the same estuary, to determine whether these two species compete for the same prey items. Both species occupy similar estuarine habitats, but S. temminckii has a much wider distribution and also occurs in the marine environment. Our results show that even though both pipefish species prey on three major invertebrate classes (Gastropoda, Malacostraca and Maxillopoda), the relative proportions differ. Syngnathus watermeyeri primarily targets Maxillopoda, with a single species of calanoid copepod constituting >95% of the Amplicon Sequence Variants (ASVs) identified from its faecal DNA, whereas the diet of S. temminckii mostly comprises snail and decapod crustacean larvae. Our finding supports the hypothesis that population declines and localised extirpations of S. watermeyeri during previous decades may have been the result of reductions in the abundance of calanoid copepods. Calanoids rely on freshwater pulses to thrive, but such events have become rare in the two estuaries inhabited by S. watermeyeri due to excessive freshwater abstraction for urban and agricultural use.

The silky shark Carcharhinus falciformis regularly associates with floating objects in the open ocean, resulting in relatively high levels of bycatch in industrial tuna purse seine fisheries using drifting fish aggregating devices (FADs). This bycatch has contributed to concerns regarding the sustainability of this fishery and its impact on silky shark populations. To investigate fishery interactions, movements of 28 silky sharks (86–235 cm TL, mean = 118 cm) fitted with pop-up and archival tags in the western Indian Ocean, between 2010 and 2012, were examined. Monthly overlap between probability surfaces of sharks and two fishery metrics (FAD-tuna catches and FAD positions) were calculated. Vertical habitat use overlapped almost entirely with operational gear depth. Horizontal movements were extensive (3–5024 km) and covered large areas of the western Indian Ocean. Monthly overlap with FAD distributions was consistently high (64.03–100%) highlighting the need for compliance with FAD design regulations to avoid entanglement. Monthly overlap with tuna catches was more variable (8.43–51.83%). The observed movement patterns suggest static spatial management measures would be have limited conservation impact, however dynamic approaches could be appropriate. Limiting fishery activities directly will likely have the greatest conservation outcomes for silky sharks in the purse seine fishery.

Defining the home range of vulnerable species is critical for designing effective spatial management strategies. However, animal home ranges often change with ontogeny and quantifying the associated temporal and spatial changes is particularly challenging for mobile marine species. Here, we investigate how the space use of a top predatory reef-associated fish (Caranx ignobilis) scales with body size. We tagged 17 individuals, representing a wide range of sizes (40.5 – 120 cm fork length (FL)), with acoustic transmitters, and passively tracked them for over 3 years at a tropical island and atoll in the Republic of Seychelles, Western Indian Ocean. We found that a sheltered atoll environment was critical for juvenile fish (< 60 cm FL) that exhibited a shift in home range location and area as they matured into adults. Small (60 – 100 cm FL) and large (> 100 cm FL) adult fish appeared to favour shallow coral reefs and associated reef drop offs whilst sharing a similar core home range location. Large adult fish, however, utilized a greater diversity of habitat types and had significantly (p < 0.05) greater annual dispersal distances (mean = 35.29 km, max = 91.32 km) than small adults (mean = 13.72 km, max = 21.55 km). Additionally, the home range (represented by minimum convex polygons) of large adults (mean = 209.74 km2) was significantly (p < 0.05) larger than that of juveniles (mean = 38.73 km2) and small adults (77.32 km2) and there was a significant (p = 0.02) relationship between fish length and home range size, with fish length accounting for 32% of the home range size variance. Furthermore, tagged fish took up to 34 months (mean = 18.54) to utilize the full extent of their home range. The habitat shift and expansion in home range size throughout ontogeny exhibited by C. ignobilis in this study should be taken into account when designing effective spatial management plans for the species.

Most batoids are mesopredators and are often hypothesised to play important ecological roles. However, a comprehensive understanding into these roles remains limited given the paucity of information of their trophic habits. St. Joseph Atoll ( $$5.43^{\circ }\hbox { S}$$ , $$53.35^{\circ }\hbox { E}$$ ) is a remote ecosystem that hosts a resident assemblage of dasyatids (Pastinachus ater, Urogymnus granulatus, and U. asperrimus). Both stomach contents (SC) and stable isotope samples (SI) ( $$\delta ^{15}\hbox {N}$$ and $$\delta ^{13}\hbox {C}$$ ) were collected in 2015 and used to investigate the trophic niches of this dasyatid assemblage and whether these niches differed inter- and intra-specifically. Dasyatid muscle samples as well as baseline samples of potential prey species and primary producers were collected for SI analyses. SC data highlighted significant inter-specific differences in diet, U. granulatus juveniles mostly consumed decapod crustaceans (Callianassidae and Portunidae) and P. ater juveniles mostly consumed bivalve molluscs. The mean species trophic positions for juveniles of all three species ranged from 2.9 to 3.6 when calculated using $$\delta ^{15}\hbox {N}$$ and from 3.4 to 3.6 when calculated using stomach content data. Analysis of $$\delta ^{13}\hbox {C}$$ showed that all juveniles were reliant upon the same carbon resources (primarily derived from seagrass beds) at the base of the food web. Diet appeared to change with size as larger individuals displayed lower $$\delta ^{13}\hbox {C}$$ and higher $$\delta ^{15}\hbox {N}$$ compared to smaller juveniles. Additionally, isotope values of the smallest individuals were similar to the largest individuals, suggesting maternal meddling. The identified patterns of inter- and intra-specific trophic niche differentiation may be indicative of competitive effects and contributes to the understanding of mesopredators in community trophic dynamics.

WOS:000579495700004; Multispecies aggregations at floating objects are a common feature throughout the world's tropical and subtropical oceans. The evolutionary benefits driving this associative behaviour of pelagic fish remains unclear and information on the associative behaviour of non-tuna species remains scarce. This study investigated the associative behaviour of oceanic triggerfish (Canthidermis maculata) and rainbow runner (Elagatis bipinnulata), two major bycatch species in the tropical tuna purse seine fishery, at floating objects in the western Indian Ocean. A total of 24 rainbow runner and 46 oceanic triggerfish were tagged with acoustic transmitters at nine drifting FADs equipped with satellite linked receivers. Both species remained associated with the same floating object for extended periods; Kaplan-Meier survival estimates (considering the censored residence time due to equipment failure and fishing) suggested that mean residence time by rainbow runner and oceanic triggerfish was of 94 and 65 days, respectively. During daytime, the two species increased their home range as they typically performed short excursions (\textless2 h) away from the floating objects. Rainbow runner performed more excursions per unit time than oceanic triggerfish; the mean excursion index was 0.86 (±0.8 SD) for oceanic triggerfish and 1.31 (±1.1 SD) for rainbow runner. Ambient light intensity appears to be the stimulus triggering the onset and end of the associative modes. The observed prolonged residency of these two major bycatch species suggests that they are more vulnerable to the tropical tuna purse seine gear than the targeted tuna species.

WOS:000558450600011; International audience; Owing to difficulties in accessing the vast open ocean, the beta (β) diversity of pelagic fish assemblages remains poorly studied. We investigated the relationship between assemblage similarity and geographical distance between anchored fish aggregating devices (FADs), sampled by standardised underwater visual censuses in three anchored FAD arrays in the Indian Ocean—at the Maldives, the Seychelles and Mauritius. The use of two complementary indices of β-diversity, based on presence/absence data (Jaccard similarity coefficient) and abundance data (Bray–Curtis index), revealed that geographical distance between sampling sites (from 4 to 257 km) appeared to have no effect on the similarity of fish assemblages associated with FADs within each array. The results of this preliminary study question the generalisation of the paradigm of an increase in β-diversity with geographic distance to the open-ocean fish community. Large-scale studies using a variety of datasets should be conducted to further investigate patterns of β-diversity in the open ocean.

A previous study that explored the age and growth of red steenbras Petrus rupestris (Valenciennes, 1830), a large sparid (family Sparidae, seabreams or porgies) endemic to South Africa and reported...

On 15 November 2017 the mouth of the West Kleinemonde Estuary breached following heavy catchment rains and increased river flow. The water level in the estuary following mouth opening decreased by ...

The Acoustic Tracking Array Platform (ATAP) is a marine science programme that monitors the movements and migrations of inshore marine animals along the South African coastline. Acoustically tagged...

The estuarine movement patterns of Mugil cephalus (Mugilidae) in response to Harmful algal blooms (HABs) was investigated in the eutrophied Sundays Estuary on the warm temperate coast of South Africa. The movements of six tagged M. cephalus (31–35 cm FL) were manually tracked using a Vemco VR100 acoustic receiver over 27 days during the typical summer bloom period. Fish were released above, within and below the mesohaline zone where Heterosigma akashiwo bloom maxima are known to occur. Physico-chemical variables and chlorophyll-a biomass were collected at each fish location and at four bloom monitoring sites, which locations were based on surface water salinity of 18, 10, 8 and 5. Mugil cephalus mostly occupied the upper mesohaline to lower oligohaline zones moving with the tidal ebb and flow. Phytoplankton biomass peaked at sites with a salinity of 10 and 8, with tagged fish only briefly (

Decreasing populations of common estuary-associated marine fishes are being documented globally and red flags associated with such declines are often ignored due to the high relative abundance of these species when compared to more rare and threatened taxa. The Cape stumpnose Rhabdosargus holubi (Steindachner 1881) is an abundant and widespread southern African sparid that is dependent on estuaries as a primary nursery area. Historical and current information on the species is comprehensive and the accumulated evidence strongly suggests that this ubiquitous fish is under pressure, mainly due to degradation of estuaries and associated catchments, increasing fishing pressures from recreational and subsistence anglers, habitat loss relating to reduced submerged macrophyte areas in many systems, industrial and agricultural pollution, infrastructural developments in and around estuaries, and climate change. In particular, the temporary loss of Lake St Lucia, which accounts for approximately 50% of the estuarine surface area in South Africa, has drastically reduced the nursery area availability for R. holubi on the subcontinent. Overall we present strong evidence to support the hypothesis that present-day stocks of R. holubi are much smaller than those in the pristine state and that urgent management measures need to be considered and implemented to prevent current depleted populations of the species from declining further.

Electronic tags are significantly improving our understanding of aquatic animal behavior and are emerging as key sources of information forconservation and management practices. Future aquatic integrative biology and ecology studies will increasingly rely on data from electronictagging. Continued advances in tracking hardware and software are needed to provide the knowledge required by managers and policymakersto address the challenges posed by the world’s changing aquatic ecosystems. We foresee multiplatform tracking systems for simultaneouslymonitoring the position, activity, and physiology of animals and the environment through which they are moving. Improved data collection willbe accompanied by greater data accessibility and analytical tools for processing data, enabled by new infrastructure and cyberinfrastructure. Tooperationalize advances and facilitate integration into policy, there must be parallel developments in the accessibility of education and training,as well as solutions to key governance and legal issues

A total of 21 juvenile Cape stumpnose (Rhabdosargus holubi) were tagged with internal acoustic transmitters in the lower, middle and upper reaches of the Kowie Estuary, South Africa. The movements of all fishes were continually monitored for five months using 22 stationary data-logging acoustic receivers, positioned along the length of the estuary. Diel and tidal cycles were identified in the movements of several individual R. holubi; however the lack of extensive movements for most individuals emphasised high residency of the species to particular sections of the estuary. River inflow and water temperature significantly affected the movement behaviour of most tagged R. holubi. Periods of increased freshwater inflow and rising riverine temperatures prompted certain individuals to shift their position downstream, while reduced sea temperatures in the lower reaches prompted certain individuals to shift their position further upstream from the mouth. Given the predicted effects of climate change in the study region, which include increased river inflow due to catchment rainfall and decreased sea temperatures due to ocean upwelling, these results suggest that R. holubi may be sensitive to the environmental effects of global warming and that the distribution and movement behaviour of this species in southern African estuaries is likely to be affected as climate change proceeds.

Two endemic southern African pipefish species (Teleostei: Syngnathidae) co-occur in estuaries on the southeast coast of South Africa. The larger longsnout pipefish, Syngnathus temminckii , is abundant and has a wide range that comprises coastal and estuarine habitats in all three of the region's marine biogeographic provinces. In contrast, the smaller estuarine pipefish S . watermeyeri is critically endangered, and confined to a few warm-temperate estuaries. Here, we explore reasons for these considerable differences in conservation status. Fecundity is related to fish size, with large live-bearing S . temminckii males carrying up to 486 developing eggs/embryos, compared to a maximum of only 44 recorded for S . watermeyeri . Loss of submerged seagrass habitats due to episodic river flooding appears to be correlated with the temporary absence of both species from such systems. Prolonged cessation in river flow to estuaries can cause a collapse in estuarine zooplankton stocks, a food resource that is important to pipefish species. The greater success of S . temminckii when compared to S . watermeyeri can be attributed to the former species' wider geographic distribution, fecundity, habitat selection and ability to use both estuaries and the marine environment as nursery areas. Genetic data indicate that this has resulted in a much smaller long-term effective population size of S . watermeyeri , a situation that has persisted since the beginning of the present interglacial period. Syngnathus watermeyeri is thus naturally more susceptible to anthropogenic disturbances, which have resulted in an alarming reduction in its contemporary population size. Possible measures to promote the conservation of S . watermeyeri are presented.

This study provides a quantitative account of fish predation by piscivorous birds in the temporarily open/closed East Kleinemonde Estuary and represents the first global attempt to simultaneously relate such consumption to production by a fish community in the same estuary. Cormorants and herons were the dominant predators and seasonal variations in the avifaunal community composition were noted. Based on comprehensive counts over three years, the piscivorous bird population was estimated to have consumed a maximum of 4 414 kg of fish in 1994, 2 400 kg in 1995/96 and 2 960 kg in 2004/05. In 1995/96 fish production in the East Kleinemonde Estuary (55.89 g m-2 a-1) was estimated at 9 780 kg and maximum bird predation amounted to 25% of annual fish production within the system over the same period, assuming that all birds counted on the estuary foraged there and that the diet of these birds comprised only fish. The above 1995/96 figures, together with an estimate of fish predation by the dominant piscivorous fish Lichia amia of 696 kg suggests that birds are probably the single most important natural predator of fishes within this estuary. An unusual mass invasion by marine Cape Cormorants Phalacrocorax capensis during July 1994 was responsible for large-scale predation of fish (2 155 kg) and resulted in the population of estuary-associated marine fishes declining from approximately 63 300 to about 18 600 individuals during the 1994 closed phase. Given that little or no marine fish recruitment was possible while the estuary mouth was closed, piscivorous birds are likely to have a higher predatory impact on populations of juvenile marine fishes in small temporarily closed estuaries than in larger permanently open systems.

Fifty-five juvenile porcupine ray Urogymnus asperrimus were collected in the isolated St Joseph Atoll, Seychelles. Stomach contents were sampled using non-lethal gastric lavage to determine the dietary composition, degree of prey selectivity and whether sex or size affected their diet. Sediment samples were collected to quantify prey availability so that prey selectivity could be estimated. Two phyla (Sipuncula and Nemertea) and 11 polychaete and crustacean families were recorded in stomach contents. Juvenile U. asperrimus appeared to specialize on one polychaete family, Capitellidae, which was the most important prey item (index of importance = 35%). This polychaete family was also most abundant in the sediment samples and U. asperrimus are thus considered opportunistic predators. There was evidence of a size-related shift in the crustacean families consumed by juvenile U. asperrimus. Data collected at this remote location provides important baseline ecological information that may prove useful in developing conservation strategies for this ecologically important species.

White stumpnose Rhabdosargus globiceps is the main target of the linefishery in Saldanha Bay. Increased fishing pressure over the last three decades, particularly by the recreational sector, has led to concerns regarding sustainability of the local white stumpnose stock. The fishery was exceptionally productive between 2006 and 2008, with an estimated annual catch of 141.2 tonnes (t). Only 3% of boat outings surveyed were commercial boats targeting white stumpnose, yet this sector accounted for 39.3 t (31%) of the average annual catch. The recreational boat sector accounted for most of the catch (70.0 t), and the recreational shore sector the least (31.9 t). Commercial boat catch per unit effort (CPUE; 3.7 fish angler –1 h –1 ) was more than 10 times that of recreational boats (0.3 fish angler –1 h –1 ). White stumpnose catch length-frequency differed significantly ( p 95%) in survey data for juvenile white stumpnose CPUE (2007–2016) indicate that the current rate of exploitation is not sustainable. Recovery of the white stumpnose stock will require a decrease in fishing mortality. Possible management regulations include sector-specific effort limitations, extending the ‘no take’ marine protected area, reducing the recreational-sector bag limit to 5 fish person –1 day –1 , implementing a commercial-sector bag limit, and increasing the minimum size limit to 30 cm TL. Keywords: angling, annual yield, catch and effort, Langebaan Lagoon, linefish, recruitment survey, roving creel survey, temperate sparid

Understanding the level of connectivity between estuarine and coastal waters is essential for appropriate management of estuarine-associated taxa. Most studies have focused on the role of a single estuary, while limited research exists on the importance of multiple estuaries to individuals of estuarine-associated species. This study used acoustic telemetry to assess the usage of multiple estuaries and coastal waters by the estuarine-dependent spotted grunter Pomadasys commersonnii. Twenty-six adult fish were tagged with acoustic transmitters in the Kariega and Bushmans estuaries, South Africa, and their movements along a 300-km stretch of Indian Ocean coastline were monitored for up to 17 months. Tagged individuals spent most of their time in the estuary where they were tagged (55% and 85% for fish tagged in the two estuaries, respectively), followed by time in the sea (30% and 15%) and in other estuaries (15% and

Understanding and characterising movement and area-use patterns of fishes within estuaries, as well as understanding the degree of connectivity between estuaries and the marine environment, can provide important insights into a species’ ecology, which is fundamental for effective management and conservation. Mark-andrecapture data obtained from the 082 TAG FISH Project, a dart-tagging programme, were used to describe movement patterns of juvenile leervis Lichia amia in the permanently open Swartkops Estuary, South Africa, as well as the degree of connectivity with the adjacent marine environment. A total of 628 juvenile leervis were tagged from 2008 to 2015, of which 77 fish (12.3%) were recaptured, with juveniles comprising 85.7% of all measured recaptures. The majority of recaptures (75.3%) were made within the Swartkops Estuary, indicating estuarine philopatry, with 23.4% having moved less than 1 km, revealing site fidelity, but most (51.9%) displaying estuarine roaming. A smaller portion of recaptures (27.7%) had dispersed to other habitats; 16 (20.8%) displayed multiplehabitat connectivity, while only 3 (3.9%) had undertaken long-distance movements (>100 km) and were recaptured up to 825 km northeast of the Swartkops Estuary. Lichia amia that had moved greater distances were characterised by a greater mean size and age at the time of recapture. This study provides valuable information on the philopatry and dispersal of juvenile L. amia.Keywords: estuary-dependent fish, mark and recapture, migration, movement behaviour, site fidelity

The silky shark Carcharhinus falciformis is commonly associated with floating objects, including fish aggregating devices (FADs), in the Indian Ocean. While the motives for this associative behaviour are unclear, it does make them vulnerable to capture in the tuna purse seine fishery that makes extensive use of FADs. Here, the diet of 323 C. falciformis, caught at FADs in the Indian Ocean, was investigated to test the hypothesis that trophic benefits explain the associative behaviour. A high proportion of stomachs with fresh contents (57%) suggested that extensive feeding activity occurred while associated with FADs. Multiple dietary indices showed that typical non-associative prey types dominated, but were supplemented with fishes typically found at FADs. While the trophic benefits of FAD association may be substantial, our results suggest that associative behaviour is not driven solely by feeding.

Physical and/or physiological constraints are assumed to isolate fish populations confined to or dependent on estuarine habitats. Strong isolation by distance is thus expected to affect connectivity. Such structuring has important implications for sustainable utilisation and replenishment of estuarine stocks that are heavily exploited. Here we present a preliminary investigation of the phylogenetic relationships of the riverbream ( Acanthopagrus species) along the southern African coast and the geographic genetic structure of what appears to be a locally endemic species or lineage. Mitochondrial DNA (mtDNA) cytochrome b sequences support the notion that the species occurring along the southern African coast is A. vagus and not A. berda as previously thought. Yet, the taxonomy of this widespread Indo-West Pacific species or species-complex requires more in-depth investigation. No genetic differentiation was detected among estuarine populations of A. vagus based on the analyses of mtDNA ND2 gene sequences and 10 polymorphic nuclear microsatellite markers. The star-like genealogy and statistical analyses are consistent with a recent population expansion event. Spatial analyses of microsatellite genotypes fail to reject the null hypothesis of panmixia, indicative of a recent population expansion or ongoing gene flow between different estuaries. The northern localities were identified as containing most of the observed variation. This study not only provides insight into the phylogenetic relationship of A. vagus relative to other Acanthopagrus species but also sheds light on the demographic history and contemporary gene flow of the species.