Overfishing is the primary cause of marine defaunation, yet declines in and increasing extinction risks of individual species are difficult to measure, particularly for the largest predators found in ...the high seas
. Here we calculate two well-established indicators to track progress towards Aichi Biodiversity Targets and Sustainable Development Goals
: the Living Planet Index (a measure of changes in abundance aggregated from 57 abundance time-series datasets for 18 oceanic shark and ray species) and the Red List Index (a measure of change in extinction risk calculated for all 31 oceanic species of sharks and rays). We find that, since 1970, the global abundance of oceanic sharks and rays has declined by 71% owing to an 18-fold increase in relative fishing pressure. This depletion has increased the global extinction risk to the point at which three-quarters of the species comprising this functionally important assemblage are threatened with extinction. Strict prohibitions and precautionary science-based catch limits are urgently needed to avert population collapse
, avoid the disruption of ecological functions and promote species recovery
.
Microplastics: No Small Problem for Filter-Feeding Megafauna Germanov, Elitza S.; Marshall, Andrea D.; Bejder, Lars ...
Trends in ecology & evolution (Amsterdam),
April 2018, 2018-Apr, 2018-04-00, 20180401, Letnik:
33, Številka:
4
Journal Article
Recenzirano
Microplastic pollution can impact filter-feeding marine megafauna, namely mobulid rays, filter-feeding sharks, and baleen whales. Emerging research on these flagship species highlights potential ...exposure to microplastic contamination and plastic-associated toxins. Research and its wide communication are needed to understand the magnitude of the issue and improve marine stewardship.
Manta rays (Genus Manta) are economically important for fisheries and tourism in Indonesia. These species have been listed by the International Union for the Conservation of Nature Red List as ...Vulnerable to extinction; therefore, human exploitation of manta rays must be regulated. A better understanding of the habitat use and movement patterns of manta rays in Indonesia is needed in order to employ effective conservation measures. To gain better insight into the movements of Manta alfredi we used 'Manta Matcher', an online database with an integrated automated matching algorithm, to compare photographs from 2,604 encounters of M. alfredi collected by recreational divers and dive operators throughout Indonesia over a nine-year period. This photographic comparison revealed that manta rays migrated between regional sanctuaries such as Nusa Penida, the Gili Islands, and the Komodo National Park (up to 450 km straight-line distance). The areas between these sanctuaries are heavily fished and trafficked by ships, and when manta rays travel through these regions they risk being fished and injured by ship strikes. These long-range manta ray movements suggest connectivity between M. alfredi populations in neighboring islands and raise concerns about the future management of regional populations. It is recommended that a national conservation strategy be developed to protect the remaining populations in the country.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Two separate sightings, two years apart, of the mimic octopus Thaumoctopus mimicus Norman & Hochberg, 2005 are reported from the Inhambane Province of southern Mozambique within the protected waters ...of the Vilanculos Coastal Wildlife Sanctuary. Individuals were encountered in May 2020 and 2022 in shallow waters, at a depth of less than 30 cm. Both individuals were fully exposed moving along a sandy substrate at the water's edge in a tidal flat. These represent the first documented sightings of T. mimicus in Mozambique, confirming the occurrence of the species along the eastern coast of Africa and extending this species' known range west from the Arabian Sea and south from the Red Sea.
Assessing the trophic role and interaction of an animal is key to understanding its general ecology and dynamics. Conventional techniques used to elucidate diet, such as stomach content analysis, are ...not suitable for large threatened marine species. Non-lethal sampling combined with biochemical methods provides a practical alternative for investigating the feeding ecology of these species. Stable isotope and signature fatty acid analyses of muscle tissue were used for the first time to examine assimilated diet of the reef manta ray Manta alfredi, and were compared with different zooplankton functional groups (i.e. near-surface zooplankton collected during manta ray feeding events and non-feeding periods, epipelagic zooplankton, demersal zooplankton and several different zooplankton taxa). Stable isotope δ(15)N values confirmed that the reef manta ray is a secondary consumer. This species had relatively high levels of docosahexaenoic acid (DHA) indicating a flagellate-based food source in the diet, which likely reflects feeding on DHA-rich near-surface and epipelagic zooplankton. However, high levels of ω6 polyunsaturated fatty acids and slightly enriched δ(13)C values in reef manta ray tissue suggest that they do not feed solely on pelagic zooplankton, but rather obtain part of their diet from another origin. The closest match was with demersal zooplankton, suggesting it is an important component of the reef manta ray diet. The ability to feed on demersal zooplankton is likely linked to the horizontal and vertical movement patterns of this giant planktivore. These new insights into the habitat use and feeding ecology of the reef manta ray will assist in the effective evaluation of its conservation needs.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The giant oceanic manta ray
Mobula birostris
was listed in the US Endangered Species Act as a threatened species in 2018, yet insufficient data exist on manta populations throughout US waters to ...designate critical habitat. Taxonomic and genetic evidence suggests that manta rays in the Western Atlantic are a separate species (
M.
cf.
birostris
) and little is understood about the ecology and life history of this putative species. The juvenile life stage of both
M. birostris
and
M.
cf.
birostris
is particularly understudied. Here, we are the first to describe the characteristics of a manta ray population along a highly developed coastline in southeastern Florida using boat-based surveys and photo identification of individuals. Fifty-nine manta individuals were identified between 2016 and 2019. All males were sexually immature based on clasper development, and 96% of females were classified as immature based on size and absence of mating scars or visible pregnancies. Twenty-five (42%) individuals were observed more than once during the study period and 8 individuals were sighted over multiple years. The occurrence of juveniles, high site fidelity and extended use of the study area by juvenile manta rays suggest that southeastern Florida may serve as a nursery habitat. High occurrence of fishing line entanglement (27% of individuals) and vessel strike injury were documented, and rapid wound healing was observed. Future research and conservation efforts will focus on identifying the physical and biological features of the potential nursery habitat and on mitigation of anthropogenic impacts.
Opportunistic in‐water and aerial surveys in South Africa and the analysis of contributed citizen science data have extended the known range of reef manta rays Mobula alfredi along the eastern coast ...of Africa by 140 km (to Mdumbi Beach) and verified the first transboundary movements for the species. Additionally, six new long‐range dispersal records have provided evidence of connectivity with the M. alfredi population off the Inhambane coastline of Mozambique. Five of these records captured one‐way movements, the longest of which was an individual that travelled 505 km from Praia do Tofo to Sodwana Bay with 301 days between sightings. A single individual made a return trip between Závora, Mozambique and Sodwana Bay, South Africa (a total distance of ~870 km). These findings support the Convention on Migratory Species listing for the species, suggesting regional transboundary management units are warranted for this wide‐ranging elasmobranch.
Understanding how individual behavior shapes the structure and ecology of populations is key to species conservation and management. Like many elasmobranchs, manta rays are highly mobile and ...wide-ranging species threatened by anthropogenic impacts. In shallow water environments, these pelagic rays often form groups and perform several apparently socially mediated behaviors. Group structures may result from active choices of individual rays to interact or passive processes. Social behavior is known to affect spatial ecology in other elasmobranchs, but this is the first study providing quantitative evidence for structured social relationships in manta rays. To construct social networks, we collected data from more than 500 groups of reef manta rays (Mobula alfredi) over 5 years in the Raja Ampat Regency of West Papua. We used generalized affiliation indices to isolate social preferences from non-social associations, the first study on elasmobranchs to use this method. Longer lasting social preferences were detected mostly between female rays. We detected assortment of social relations by phenotype and variation in social strategies, with the overall social network divided into two main communities. Overall network structure was characteristic of a dynamic fission-fusion society, with differentiated relationships linked to strong fidelity to cleaning station sites. Our results suggest that fine-scale conservation measures will be useful in protecting social groups of M. alfredi in their natural habitats and that a more complete understanding of the social nature of manta rays will help predict population responses to anthropogenic pressures, such as increasing disturbance from dive tourism.
The implications of plastic pollution, including microplastics, on marine ecosystems and species are increasingly seen as an environmental disaster. Yet few reports focus on filter-feeding megafauna ...in regions heavily impacted by plastic pollution, such as Indonesia in the Coral Triangle, a global marine biodiversity hotspot. Here, we evaluate plastic abundance and characterize debris from feeding grounds for manta rays (Mobula alfredi) and whale sharks (Rhincodon typus) in three coastal locations in Indonesia: Nusa Penida Marine Protected Area, Komodo National Park, and Pantai Bentar, East Java. A 200 µm plankton net was used to sample the top 0.5 m of the water column (‘trawl survey’) and floating plastics were assessed along ~ 440 m long transects (‘visual survey’) during the Indonesian north-west (‘wet’) and south-east (‘dry’) monsoon seasons during 2016 – 2018. Microplastics were identified visually, measured and categorized from trawl samples, and larger floating plastics were counted from vessels in visual transects. Plastic abundance ranged widely from 0.04 to 0.90 pieces m-3 (trawl survey) and 210 to 40,844 pieces km-2 (visual survey). Results from linear models showed significant seasonal and location differences in estimated plastic abundance for trawl and visual surveys in Nusa Penida and Komodo. Plastic abundance was up to ~ 44 times higher in the wet than the dry season, with the largest seasonal effect observed in Nusa Penida. Overall, small pieces 50% combined) were the most prevalent plastics. Theoretical plastic ingestion rates were calculated using estimated filtration volumes of manta rays and whale sharks and the mean plastic abundance in their feeding grounds. Upper plastic ingestion estimates for manta rays were ~ 63 and 25 pieces h-1 for Nusa Penida and Komodo locations, respectively, and ~137 pieces h-1 for whale sharks in Java. Analysis of manta ray egested material confirmed plastic ingestion, the consequences of which might include exposure to toxic plastic additives and adhered persistent organic pollutants. Communicating this information to communities who stand to benefit from healthy megafauna populations might help local governments as they work towards reducing plastics in the marine environment.
Site-specific knowledge of spatial ecology is essential for the implementation of effective conservation measures for wide-ranging marine species. We used passive acoustic telemetry to examine the ...movements and site usage of reef manta rays Mobula alfredi in the Inhambane Province of Mozambique. Acoustic receivers were installed at 14 sites spanning 350 km along the coastline. We deployed 42 acoustic transmitters on manta rays between February 2010 and November 2014. Using Brownian bridge kernel utilization distributions, (bbKUD), we estimated core (50 % bbKUD) and extent (95 % bbKUD) home ranges, and constructed spatial movement networks to examine connectivity. Manta rays exhibited site affinity and diel visitation patterns to cleaning stations, with 89.2% of detections during daylight hours, and spent up to 8.2 h at these sites (mean visit duration = 25.41 ± 2.45 min). Manta rays moved widely within the study region, and strong connectivity was evident between Praia do Tofo and Zàvora. However, no movements were recorded between the Bazaruto Archipelago and the southern sites. Existing marine protected areas (MPAs) offer protection across ~24% of the estimated extent home range, and only to animals that use the waters of the archipelago. We therefore suggest the explicit protection of critical habitats through spatial management approaches in Praia do Tofo and Zàvora and the expansion of current MPA boundaries in the Bazaruto Archipelago. Ideally, these measures should be re-enforced by prohibiting directed fishing of manta rays in Mozambique and additional restrictions on gill net usage to prevent incidental capture outside of protected areas.
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