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.
The difference in arsenic concentration and speciation between benthic (Pteromylaeus bovinus, Myliobatis aquila) and pelagic rays (Pteroplatytrygon violacea) from the northern Adriatic Sea (Gulf of ...Trieste) in relation to their size (age) was investigated. High arsenic concentrations were found in both groups with tendency of more efficient arsenic accumulation in benthic species, particularly in muscle (32.4 to 362 µg·g-1 of total arsenic). This was attributed to species differences in arsenic access, uptake and retention. In liver most arsenic was present in a form of arsenobetaine, dimethylarsinic acid and arsenoipids, whereas in muscle mainly arsenobetaine was found. The good correlations between total arsenic/arsenobetaine and size reflect the importance of accumulation of arsenobetaine with age. Arsenobetaine is an analogue of glycine betaine, a known osmoregulator in marine animals and both are very abundant in mussels, representing an important source of food for benthic species P. bovinus and M. aquila.
Total mercury (Hg) and monomethylmercury (MMHg) were analysed in the gills, liver and muscle of four cartilaginous fish species (top predators), namely, the eagle ray (Myliobatis aquila), the bull ...ray (Pteromylaeus bovinus), the pelagic stingray (Dasyatis violacea) and the common stingray (Dasyatis pastinaca), collected in the Gulf of Trieste, one of the most Hg-polluted areas in the Mediterranean and worldwide due to past mining activity in Idrija (West Slovenia). The highest Hg and MMHg concentrations expressed on a dry weight (d.w.) basis were found in the muscle of the pelagic stingray (mean, 2.529 mg/kg; range, 1.179–4.398 mg/kg, d.w.), followed by the bull ray (mean, 1.582 mg/kg; range, 0.129–3.050 mg/kg d.w.) and the eagle ray (mean, 0.222 mg/kg; range, 0.070–0.467 mg/kg, d.w.). Only one specimen of the common stingray was analysed, with a mean value in the muscle of 1.596 mg/kg, d.w. Hg and MMHg contents in the bull ray were found to be positively correlated with species length and weight. The highest MMHg accumulation was found in muscle tissue. Hg and MMHg were also found in two embryos of a bull ray, indicating Hg transfer from the mother during pregnancy. The number of specimens and the size coverage of the bull rays allowed an assessment of Hg accumulation with age. It was shown that in bigger bull ray specimens, the high uptake of inorganic Hg in the liver and the slower MMHg increase in the muscle were most probably due to the demethylation of MMHg in the liver. The highest Hg and MMHg contents in all organs were found in the pelagic stingray, which first appeared in the northern Adriatic in 1999. High Hg and MMHg concentrations were also found in prey species such as the banded murex (Hexaplex trunculus), the principal prey of the eagle rays and bull rays, the anchovy (Engraulis encrasicholus) and the red bandfish (Cepola rubescens), which are preyed upon by the pelagic stingray, as well as in zooplankton and seawater. Based on previously published data, a tentative estimation of MMHg bioamagnification was established. The average increase in MMHg between seawater, including phytoplankton, and zooplankton in the Gulf was about 10⁴, and MMHg in anchovy was about 50-fold higher than in zooplankton. The bioaccumulation of MMHg between seawater and small pelagic fish (anchovy) amounted to 10⁶ and between water and the muscle of larger pelagic fish (pelagic stingray) to 10⁷. The MMHg increase between surface sediment and benthic invertebrates (murex) and between benthic invertebrates and small benthic fish was 10². Ultimately, the trophic transfer resulted in a 10³ accumulation of MMHg between water and muscle of larger benthic fish (bull ray, eagle ray, common stingray), suggesting lower bioaccumulation by benthic feeding species.
Identification of the factors influencing the distribution of vulnerable species can be useful for predicting their occurrence at a local to regional scale and for identifying the most suitable ...measures of management and conservation. We used generalized additive models to assess the effects of spatiotemporal, environmental, and operational factors on the catches of two myliobatids: the Common Eagle Ray Myliobatis aquila and the Bull Ray Pteromylaeus bovinus. Fishing data were collected from commercial midwater trawlers operating in the north-central Adriatic Sea during 2006–2013. Presence/absence and abundance (CPUE) data were modeled separately, and eachmodel was then validated by using a test data set. The presence/absence and abundance of Common Eagle Rays and Bull Rays were mostly influenced by spatial (haul location) and temporal predictors. The major occurrences of Common Eagle Rays and Bull Rays were observed in the upper Adriatic Sea between late spring and early autumn. During winter, a southward shift in the catch was recorded for both species. In accordance with a significant effect of depth, Common Eagle Rays were more likely to be caught in hauls conducted between 10- and 60-m depths. The CPUEs of Common Eagle Rays and Bull Rays declined significantly with haul duration and net vertical opening. The validation procedure indicated that the predictive accuracy of the models was rather good. Giving new insight into the ecological requirements of Common Eagle Rays and Bull Rays, the results of this studymay contribute to the development of conservation strategies and can be used to direct future monitoring and research programs.
A specimen of bull ray Aetomylaeus bovinus was captured dead by a diver around a tuna sea cage farm. It was female, measured 2310 mm in total length (TL) and 1460 mm in disc width (DW) with body ...weight estimated as about 20 kg. This case was reported from a tuna farm for the first time. The bull ray entered the sea cage about three months ago, but no attack occurred to the tuna in the cage. It was grazing on fouling organisms that attached to the nets. However, the cage nets were replaced with clean ones four days ago before the capture, and the bull ray did not find enough fouling organisms or uneaten fish feed and was starved to death.
Uncommon fish species, some caught in deep waters, occurred in the last fifteen years at Rhodes and other Dodecanese Islands (SE Aegean Sea, Greece) and their findings are reported. They concern the ...cartilagineous fish Odontaspis ferox, Dalatias licha, Rhinobatos cemiculus, Rhinobatos rhinobatos, Gymnura altavela and the bony fish Sudis hyalina, Nemichthys scolopaceus, Chlopsis bicolor, Apterichthus anguiformis, Apterichthus caecus, Regalecus glesne, Diplodus cervinus cervinus, Brama brama, Lampris guttatus and Luvarus imperialis. Information on the findings of other eleven species, with a poorly known local occurrence, like Galeus melastomus, Oxynotus centrina, Torpedo nobiliana, Dipturus oxyrinchus, Pteromylaeus bovinus, Mobula mobular, Ariosoma balearicum, Hoplostethus mediterraneus, Aphia minuta, Parablennius incognitus and Mola mola is also given. The records add knowledge on the Hellenic ichthyofauna diversity and on the distribution of these species in the Eastern Mediterranean.
Quinze Pteromylaeus bovinus (Geoffroy St. Hilaire), péchés en divers points de la côte tunisienne, ont été examinés entre 1996 et 1998 pour l'étude de leurs parasites. Myliocotyle pteromylaei gn. et ...sp. n., récolté sur les branchies de douze individus hôtes, est décrit et illustré. Le genre et l'espèce diffèrent des autres Heterocotylinae par le nombre et la morphologie des structures dorsales du hapteur, la disposition et le nombre des glandes antérieures et la morphologie du pénis. O. pteromylaei marque avec Heliocotyle kartasi l'originalité des Monocotylidae parasites branchiaux de Pteromylaeus bovinus.
Fifteen specimens of Pteromylaeus bovinus (Geoffroy St. Hilaire) from the Tunisian coast were examined for ectoparasites during 1996-1998. Myliocotyle pteromylaei gn. et sp. n. found on gills of twelve host specimens is described and illustrated. It differs from other Heterocotylinae mainly by the number and morphology of haptoral dorsal structures, arrangement and number of the anterior glands and morphology of the penis. M. pteromylaei, along with Heliocotyle kartasi, illustrates the originality of monocotylids gill parasites of Pteromylaeus bovinus
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