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Many ray species are threatened with extinction, and so understanding their movement and habitat use is vital for developing effective management and conservation efforts. Globally, rays are known to rely on estuarine habitats, but estuary use by rays has not yet been investigated in South Africa. Thirty-three diamond rays Gymnura natalensis and 25 bull rays Aetomylaeus bovinus, both species anecdotally recorded to occur in estuaries, were acoustically tagged. Individuals were tracked using a nation-wide network of receivers in South Africa, the Acoustic Tracking Array Platform (ATAP), that has acoustic receivers in both marine and estuarine environments. Only six rays (4 diamond and 2 bull rays) were recorded using estuaries, but they displayed seasonal philopatry, returning to specific estuaries during spring to autumn months (September to May) for up to 6 consecutive years. Due to a number of rays entering the Breede Estuary, the fine-scale habitat use in this ecosystem was investigated. Marine-estuarine connectivity was significantly influenced by marine temperatures. Additionally, presence in the upper parts of the Breede Estuary (up to 17 km from the mouth) was influenced by temperature, tides and time of day. Findings suggest estuaries are an important, and previously overlooked, habitat type for a portion of the diamond and bull ray populations on the south coast of South Africa, which has management and conservation implications. [ABSTRACT FROM AUTHOR]

The blue stingray Dasyatis chrysonota is an important and endemic coastal inhabitant of southern African coastal waters however, it is listed as Near Threatened with declining populations. Understanding it's spatial ecology in the context of current Marine Protected Areas (MPAs) is vital to not only inform population dynamics and ecological roles, but to determine whether currently zoned MPAs can provide sufficient protection to this species. Twenty-seven individuals were monitored using the Acoustic Tracking Array Platform (ATAP—a nation-wide collaborative network of acoustic receivers) for up to 4.5 years. Individuals displayed site affinity to defined regions of the coast, with the majority of detections for most individuals being recorded in the shallow bay/coastal shelf they were tagged in. However, important movement corridors linking different habitats were also identified (inshore vs offshore and coastal bay vs coastal shelf habitats). This habitat use varied monthly and was influenced by temperature, with individuals displaying restricted movements to the shallow bay habitat in summer when deeper waters were much colder. The large collaborative nature of the ATAP allowed for the monitoring of a benthic ray across large spatial scales for the first time, challenging preconceived notions that small undulatory batoids cannot travel large distances (many individuals were found to travel up to 200 km). Insights can also assist in local management of this species, and highlight that current MPA zonation may not be sufficient to protect blue stingrays from further population declines. [ABSTRACT FROM AUTHOR]

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 ∘ S , 53. 35 ∘ 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) ( δ 15 N and δ 13 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 δ 15 N and from 3.4 to 3.6 when calculated using stomach content data. Analysis of δ 13 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 δ 13 C and higher δ 15 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The purpose of this study was to test the hypothesis that an estuarine species as the spotted grunter Pomadasys commersonnii is evenly distributed within the estuary and uniformly exploited by different groups of fishers. This was done by investigating the movements and area use of spotted grunter in relation to the fisheries. The position of 20 acoustically tagged fish was recorded during 36 days in February and March 2003, by manual tracking and automated data logging receivers. Information on the fisheries in the estuary was collected through visual registration of fishing effort and interviews. The spotted grunter moved on average 1.0 km (SD ± 0.7) between positional fixes. Most of the fish were positioned in the lower part of the 12 km long estuary, as 70% of the positional fixes were within the first 3 km, and 89% within the first 6 km. Approximately half (49%) of all the fixes were between 1.0 and 1.5 km from the estuary mouth. The spotted grunter used on average 4.9 km (SD ± 4.9) of the length of the estuary, and there was no significant relationship between the length of the estuary used and the body length of the fish (26–39 cm TL). Subsistence fishers accounted for 73% of fishing lines in the water, while recreational fishers accounted for the rest. Ninety-three percent of the lines were recorded within the first 6 km from the estuary mouth, of which 80% were recorded within the first 3 km. Almost 1/3 of the fishing effort was recorded between 1.0 and 1.5 km from the mouth. The hypothesis that the estuarine dependent species spotted grunter was evenly distributed within the estuary was rejected. However, there was a significant relationship between the distribution of the fishing effort of the subsistence fishers and the fish, indicating that the spotted grunter was uniformly exploited within the estuary by this group of fishers. In contrast, there was no relationship between the distribution of fish and recreational anglers. [ABSTRACT FROM AUTHOR]

This study compared the ichthyofaunal assemblages in 10 Eastern Cape Province, South Africa, estuaries to identify whether there were any structural variations between the assemblages and to determine the environmental and physical factors linked to these variations. Species belonging to both the marine migrant and estuarine resident groups, by consistent representation within each estuary grouping, were responsible for the separation of fish assemblage structures between the different types of systems. The data further revealed that fish assemblages in the three main types of estuaries investigated were distinct, linked primarily to estuary mouth status and estuary size. [ABSTRACT FROM AUTHOR]

Acoustic tracking is a commonly used method to study the movement ecology of marine species. The characteristics of the data collected are not simply functions of the location of the tagged animal as they are also influenced by the method of data collection and its sampling frequency. In particular, since the data are acoustically driven, the significance of any result hinges not only on the accuracy of the equipment but also on the reliability of the information received. While passive acoustic telemetry requires an evaluation of the detection efficiency of receivers moored in different habitats (or sites) to obtain reliable data, active acoustic telemetry requires more field-related information on how to best track tagged animals without impacting on their natural behaviour. This study aimed to evaluate the reliability of active acoustic telemetry data in a temperate coastal environment. This was achieved by conducting a series of field experiments to assess (i) the use of signal strength-to-infer distance to the tracked animal under different tracking conditions, (ii) what signal strength threshold can be used to obtain reliable bio-telemetered data, (iii) whether the behaviour of a tracked animal would be a main concern in terms of data reliability, and (iv) the best filtering option to reduce the data to be analysed. The findings yielded a signal strength-to-distance relationship to improve the accuracy of the positional fixes of actively tracked animals, which can be used as a practical reference for future tracking studies on pelagic species in temperate coastal environments. [ABSTRACT FROM AUTHOR]