The trophic and spatial ecology of a sympatric dasyatid community at a remote Atoll, Seychelles

Batoid populations are declining globally but the paucity of information makes management or conservation efforts difficult. Additionally, batoids are mesopredators and are hypothesised to play important ecological roles, but a comprehensive understanding of these roles is also limited. Therefore, information on batoid habitat use, foraging ecology, and resource partitioning is needed. St. Joseph Atoll is a relatively pristine ecosystem that hosts a sympatric dasyatid community (Pastinachus sephen, Urogymnus granulatus, and U. asperrimus). Passive acoustic telemetry identified high levels of long-term site affinity by both juvenile and adult dasyatids to St. Joseph Atoll. Dispersal from the atoll by larger juveniles was also evident. Juveniles displayed restricted horizontal movements in the atoll, but the extent of these movements differed seasonally. Stomach content and stable isotope analyses identified inter-specific prey partitioning (P. sephen juveniles were mollusc specialists and U. granulatus juveniles were crustacean specialists) and intra-specific prey partitioning. Juveniles were reliant upon a seagrass-based food web, whereas adults were reliant on phytoplankton-based food web. Adults fed at higher trophic levels compared to juveniles (mean of 4.6 and 3.4 respectively). Juvenile dasyatids preferentially selected the shallow reef at habitat of the atoll, where there was no evidence for inter-specific habitat partitioning (individuals co-occurred randomly with con-and hetero-specifics). Conversely, resident adults were more reliant on the deeper lagoon. Juveniles selected the reef at habitat likely because it provided refuge from predation and foraging opportunities. However, juveniles were also detected in the lagoon habitat and this appeared to be necessitated by physical factors as they were detected more frequently in the lagoon at low tides and when temperatures on the reef fats became too warm or too cold. All results together suggest that St. Joseph Atoll is a nursery area for these dasyatids. Juveniles may be limited by resources as prey was partitioned between species. However, top-down control by larger sharks was likely a significant influence on habitat selection, as was the physical effects of tide and temperature. Finally, St. Joseph Atoll is suitable for the designation of a Marine Protected Area, which would likely confer high conservation benefits to this dasyatid community

The trophic and spatial ecology of juvenile porcupine rays Urogymnus asperrimus at the remote St. Joseph Atoll

Little information exists for the widely occurring but rare porcupine ray Urogymnus asperrimus. This is a concern given that it is a vulnerable species and likely plays an important ecological role in tropical atoll ecosystems. The aims of this thesis were to investigate the trophic and spatial ecology of juvenile porcupine rays within the St. Joseph Atoll, which is hypothesized to be functioning as a nursery for this species. Specific objectives were to determine i) the dietary composition and resource selectivity displayed by juvenile porcupine rays, ii) residency to the atoll, space use, and seasonality in movements, and iii) whether environmental factors affect short-term movements. Gastric lavage was used to collect stomach contents from 55 juveniles and sediment samples were collected. Thirteen juveniles were implanted with acoustic transmitters and monitored for a year by an array of 88 acoustic receivers situated in and around the St. Joseph Atoll. Porcupine rays appeared to be generalist and opportunistic feeders, foraging predominantly on annelids with the highest environmental availability. Polychaetes of the family Capitellidae were the most important prey item (Index of Importance = 35%). Rays only fed on deep infaunal prey, likely because of their foraging behaviour, suggesting they may influence this community. There was a size-related shift in the crustacean families consumed. The tagged rays displayed high residency to the atoll (mean residency index of 64%) and restricted movements, with small core use and activity space areas (mean of 0.5km² and 3km² respectively) and the majority of detections were recorded within 1km of their tagging locations. The rays favoured the sand ats where 88% of detections occurred. Transient use of the lagoon and fringe reef peaked in the north-west monsoon season, indicating a seasonal usage of these habitats. The effects of temperature and water depth on movements were manifested as diel and tidal cyclical patterns in presence. Evidence illustrates that the St. Joseph Atoll constitutes an important nursery for this species, which has been declared a Marine Protected Area. A major determinant behind the dependence of this nursery habitat is related to predator avoidance. Thermoregulatory behaviours were identified, suggesting that this species is vulnerable to climate change

Stingray Habitat Use Is Dynamically Influenced by Temperature and Tides

Abiotic factors often have a large influence on the habitat use of animals in shallow marine environments. Specifically, tides may alter the physical and biological characteristics of an ecosystem while changes in temperature can cause ectothermic species to behaviorally thermoregulate. Understanding the contextual and relative influences of these abiotic factors is important in prioritizing management plans, particularly for vulnerable faunal groups like stingrays. Passive acoustic telemetry was used to track the movements of 60 stingrays at a remote and environmentally heterogeneous atoll in Seychelles. This was to determine if habitat use varied over daily, diel and tidal cycles and to investigate the environmental drivers behind these potential temporal patterns. Individuals were detected in the atoll year-round, but the extent of their movement and use of multiple habitats increased in the warmer NW-monsoon season. Habitat use varied over the diel cycle, but was inconsistent between individuals. Temperature was also found to influence stingray movements, with individuals preferring the deeper and more thermally stable lagoon habitat when extreme (hot or cold) temperature events were observed on the flats. Habitat use also varied over the tidal cycle with stingrays spending a higher proportion of time in the lagoon during the lowest tides, when movement on the flats were constrained due to shallow waters. The interplay of tides and temperature, and how these varied across diel and daily scales, dynamically influenced stingray habitat use consistently between three species in an offshore atoll.</jats:p

The effects of a marine reserve on galjoen (Dichistius capensis) at Cape Point, South Africa, and implications for the management of the recreational fishery

Marine protected areas (MPAs) are gaining credibility in the scientific community because of their duality as a conservation and fishery management tool, but sometimes the actual effects of an MPA fall short of the expected outcomes. Case-by-case studies are needed to understand what works and what doesn’t and this understanding can then be applied to decision making and adaptive management. The galjoen (Coracinus capensis), a surf zone teleost endemic to South Africa, is a popular fish for recreational shore anglers and as such the population has declined to dangerously low levels. Marine reserves were established around Cape Point to try and counteract this decline. This study aimed to determine whether these reserves are having a positive effect on galjoen mortality, density and size. A controlled shore angling program has been running on the Cape Peninsula since 1986 in which anglers use a standardised fishing technique. The anglers record the length of their fishing trip as well as the fork length of the fish they catch. Two sites located in near proximity to each other, one in a reserve and one in an exploited area, were chosen from the data set to compare. This avoided the conflicting problem of major habitat differences. General linear models (GLMs) were used to isolate the effect of area on the catch per unit effort (CPUE) as well as fork length, and a negative log-likelihood function was used to estimate the mortality rate and sex ratio for each area. CPUE increased significantly from of 1.02 ± 0.81 galjoen.angler-¹.hour-¹ in the exploited area to 1.48 ± 0.85 galjoen.angler-¹.hour-¹ in the protected area and fork length increased significantly from 300.69 ± 34.71mm in the protected area to 329.31 ± 40.19mm in the exploited area. The GLMs revealed that the parameters ‘area’ and ‘year’ significantly affected the variation in CPUE and fork length, and that area had the greatest explanatory power in both cases suggesting that the reserve had a positive effect on the galjoen density and size. The mortality estimate for the protected site, which was taken as natural mortality, was 0.55 year-¹ and the mortality estimate at the exploited site was 1.0 year-¹. Fishing mortality (F) was estimated as 0.45 year-¹ which was considered to be close to FMSY. Increases in CPUE over time in the exploited area led to the hypothesis that the reserve is re-stocking adjacent exploited areas. A reduction in F over time suggested that effort is reduced in the exploited study area, but it is unknown whether this effort has been displaced to another area adjacent the reserve. Because conventional fishery management tools are difficult or impossible to enforce for the galjoen stock and because the reserves appear to be positively affecting the galjoen within the reserve, it is suggested that the reserves are the optimal and most efficient conservation and fishery management tool for the galjoen stock

Dietary niche differentiation in a mesopredatory dasyatid assemblage

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) (δ15N and δ13C) 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 δ15N and from 3.4 to 3.6 when calculated using stomach content data. Analysis of δ13C 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 δ13C and higher δ15N 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

Quest Volume 10 Number 2

Rural effluent disposal:A case for environmental education Lesley van Heerden and her team from Albert College, Prince Albert, show how we can all make a difference; Africa prepares for SKA: the African VLBI Network: Anita Loots and Mike Gaylard explain how Africa is becoming part of the global radio astronomy network; How are Antarctica and the Southern Ocean responding to climate change?: Mike Lucas, Kirti Gihwala and Michal Viskich explain how the Southern Ocean is Earth's 'freezer'; The unique pollinators of the Cape Floral Kingdom: Chris Johnson explains how an unlikely small mammal is vital to the health of the fynbos; The importance of the overlooked: the story of stingrays Chantel Elston describes the biology of this little-known species; Concrete and environmental sustainability: Olukayode Alao shows that concrete structures do not have to add to carbon emissions; Reframing climate change: Wilda Fourie-Basson shows how climate change is a social science issue; A skin photosensitivity atlas for South Africa; Caradee Wright looks at our sensitivity to the sun; News from the University of Pretoria: Beefing up efforts to breed with cattle • Study asks for ban on 4x4s in protected areas; Ostriches can't choke or taste; New technique finds anti-HIV compounds in indigenous plant species; Haviside's dolphins on the West Coast are related; Images of long bones used to identify children; Decoding of Eucalyptus tree genome unlocks new possibilities for renewable fibre, fuel, and biomaterials.Rural effluent disposal:A case for environmental education Lesley van Heerden and her team from Albert College, Prince Albert, show how we can all make a difference; Africa prepares for SKA: the African VLBI Network: Anita Loots and Mike Gaylard explain how Africa is becoming part of the global radio astronomy network; How are Antarctica and the Southern Ocean responding to climate change?: Mike Lucas, Kirti Gihwala and Michal Viskich explain how the Southern Ocean is Earth's 'freezer'; The unique pollinators of the Cape Floral Kingdom: Chris Johnson explains how an unlikely small mammal is vital to the health of the fynbos; The importance of the overlooked: the story of stingrays Chantel Elston describes the biology of this little-known species; Concrete and environmental sustainability: Olukayode Alao shows that concrete structures do not have to add to carbon emissions; Reframing climate change: Wilda Fourie-Basson shows how climate change is a social science issue; A skin photosensitivity atlas for South Africa; Caradee Wright looks at our sensitivity to the sun; News from the University of Pretoria: Beefing up efforts to breed with cattle • Study asks for ban on 4x4s in protected areas; Ostriches can't choke or taste; New technique finds anti-HIV compounds in indigenous plant species; Haviside's dolphins on the West Coast are related; Images of long bones used to identify children; Decoding of Eucalyptus tree genome unlocks new possibilities for renewable fibre, fuel, and biomaterials.Academy of Science of South Africa: Department of Science and InnovationAcademy of Science of South Africa: Department of Science and Innovatio

A systematic conservation plan identifying critical areas for improved chondrichthyan protection in South Africa

The International Union for Conservation of Nature (IUCN) estimates that over a third of all chondrichthyan species (sharks, rays and chimaeras) are threatened with extinction, primarily by overfishing (as target or bycatch species). Owing to the wide-ranging distributions of many chondrichthyans, they are often overlooked in marine protected area (MPA) design. South Africa is a biodiversity hotspot for chondrichthyan species diversity, and to improve the conservation status of these species in the country's continental exclusive economic zone (EEZ), we collaborated widely to collate existing occurrence data. Ensemble models were developed for 87 species' distributions, which informed a systematic conservation planning analysis for 64 threatened and endemic species. We assessed the current representation of these species in South Africa's MPA network and identified priority areas for protection, avoiding fishing pressure where possible. Results show that many MPAs are well placed to protect chondrichthyans, especially along the east coast (KwaZulu-Natal province). Unfortunately, permissive fishing regulations within many MPA zones reduces their effectiveness at protecting chondrichthyans. Improved regulations designed to protect chondrichthyans within all MPAs should be considered a high priority. Priority areas for increased spatial protection were identified along the west coast continental shelf, the Agulhas Bank off the south coast, and south coast embayments. We found that supplementing the current MPA network by an additional 5 % of the EEZ would be sufficient to protect >30 % of the range of all 64 species, provided there is adequate enforcement. As South Africa prepares to expand its MPA estate to meet international targets, these findings can ensure that chondrichthyans are well represented. •We collaborated widely to collate occurrence data on 164 chondrichthyan species in South Africa.•Distribution models were developed for 87 chondrichthyan species.•Priority areas for protection were identified using systematic conservation planning.•Priority areas included the shelf offshore of the west and south coast.•South Africa's MPA regulations require better management to protect chondrichthyans