Notes on the fishes of western New Guinea III. The fresh water shark of Jamoer lake

INTRODUCTION In 1954, during a visit to Hollandia, western New Guinea, it was rumoured that sharks had been observed in the fresh water of Jamoer Lake, at a distance by effluent river of about 130 km from the Arafoera Sea. For further information on the locality, including a map of the area, I refer to the first note in the present series (Boeseman, 1963: 231, fig. 6). With eagerness we welcomed an opportunity provided by Rear Admiral (at the time Captain) G. B. Fortuyn, then Commander-in-Chief Naval Forces Netherlands New Guinea, to pay a short visit to the isolated lake. All necessary facilities, including transportation and maintenance, were kindly furnished by the Royal Netherlands Naval Air Service and the Royal Marines. Accompanied by my colleagues Drs. Brongersma and Holthuis, I visited Jamoer Lake from 7 to 13 December 1954, while Dr. Brongersma revisited the lake from 22 to 26 March 1955. SHARKS IN FRESH WATER The occurrence of sharks in tropical and subtropical fresh water is not as rare as usually presumed, though the number of species involved seems limited. It is strange to find that even zoologists often are surprised to learn that sharks occur in fresh water, while the principal facts gradually have penetrated even into popular and semi-popular literature (e.g., Budker, 1947: 167-169; Schultz & Stern, 1948: 56-57; Le Danois, 1949: 148-150, 164; Herald, 1961: 26, 28, 31). As the principal summaries on the subject are outdated (Engelhardt, 1913; Scheuring, 1929, map!) or usually overlooked (Smith, 1936), it seems useful to give here a general idea of the frequency of the phenomenon in Carcharhinid sharks and of the species