Dusky shark

Abstract: Arsenobetaine has been isolated from the tail muscle of the western rock lobster (Panulirus cygnus George) and from the flesh of the dusky shark (Carcharhinus obscurus Le Sueur), both of which are commercially important seafoods. Trigonelline has also been isolated from the lobster and both arsenobetaine and trigonelline have been isolated from human urine obtained after ingestion of cooked rock lobster. The crystal structures of the monohydrates of arsenobetaine and trigonelline have been determined and a simple synthesis of arsenobetaine has been developed.

Abstract: Diet and feeding habits of the smooth dogfish, Mustelus canis, Atlantic sharpnose, Rhizoprionodon terraenovae, dusky, Carcharhinus obscurus, and the sand tiger, Carcharias taurus sharks, were investigated through analysis of stomach contents. Diet in M. canis was relatively homogeneous and was dominated by crustaceans, consisting mostly of rock crabs, Cancer irroratus. Diet in R. terraenovae was more heterogeneous and consisted largely of crustaceans and teleosts, in similar levels of prey importance. Use of cumulative prey curves as a measure of precision indicated that data were insufficient to fully describe the diets of C. obscurus and C. taurus. Nonetheless, these data suggested that both species are generalized feeders and consume a variety of teleost and elasmobranch prey. Further studies are necessary to fully characterize diet in these two species.

Abstract: In total, 28 687 large sharks were caught between 1978 and 2000 in the nets that protect users of the popular swimming beaches of KwaZulu-Natal, South Africa, against shark attack Over this 23-year period, 53 sharks (018% of the catch) were found with polypropylene strapping bands around the body Less than 1% of the individuals from each of eight species were entangled in this manner The dusky shark Carcharhinus obscurus was the most frequently entangled species, with 27 individuals (047% of the species catch) There was an increase in the incidence of entangled C obscurus with time Those examined in the laboratory were significantly underweight Although entanglement may ultimately result in death, the low incidence recorded in this study is unlikely to affect the populations of sharks concerned A total of 60 sharks (038% of those with recorded stomach contents) had ingested plastic debris The most common items were packets or sheets There was no increase in the ingestion of plastics with time The highest frequency of occurrence was in the tiger shark Galeocerdo cuvier, with 38 individuals (75% of tiger sharks examined)