2 70 THE GREAT BARRIER REEF. 



course, have been graduall}' pushed farther and farther down towards the sea, through the agencies 

 just described, fell under my personal observation in Tasmania. In the river Tamar, debouching 

 on the northern coast-line of that colony, the mud oyster, Ostrea ediilis, was originally abundant, 

 from the Heads half-way to the town of Launceston, some forty miles distant. By degrees, as 

 borne testimony to by residents of the district, the oysters have gradually disappeared from the 

 formerly prolific higher portions of that river, known as Whirlpool Reach and the Middle and 

 Eastern Arms. On my first visit to the Tamar estuary, a few oysters were still left in the lowest 

 bay, known as the West Arm, but these, both young and old, were in a dead or dying state, owing 

 chiefly to prolonged immersion in water containing an insufficient amount of saline ingredients, the 

 organic pollution, from the city of Launceston, probably also playing an important part in their 

 destruction Within a few years after this first visit, oysters were practically extinct in the 

 Western Arm, and no success attended the efforts made to resuscitate the fishery in that district 

 by artificial culture. The last lingering remnants gathered there were in a decidedly unhealthy 

 state, the shells being discoloured and wanting in solidity, and the contained oysters being in the 

 poorest possible condition. 



"Should the interpretation here suggested be correct, with relation to the diseased condition 

 of the New South Wales oyster fisheries, it is evident that the prospects are but small of recover- 

 ing the ground lost to oyster culture in the several districts affected. It will consequently be in- 

 cumbent on the oyster-growers of that colony, to make the most of the water area left to them 

 where the water is pure and not liable to be invaded by the disease, and, if they are ambitious to 

 regain that position formerly held, in which the colony was independent of supplies from external 

 sources, they will require to turn their attention to the culture of the mollusc on a far more 

 scientific basis than has been hitherto attempted in New South Wales waters." 



Concerning the suspected or prospective invasion of the Queensland oyster-beds by this mud 

 disease, with its accompanying parasitic worms, the author is in a position to report that there is, 

 at all events, no evidence to hand of its invasion at the present time. A little while since, there 

 was some suspicion of its having made its appearance in Wide Bay, and a few specimens of oysters 

 which, on being opened, were found to contain a parasitic worm, were submitted for examination. 

 The worm, however, in these solitary instances, was a nereid, representing a different genus than 

 that associated with the New South Wales disease, and had apparently gained access to the shell 

 through a perforation originally made by a boring whelk. There are circumstances which, in the 

 author's opinion, will operate for a long while, and, it is to be trusted, permanently, against the intro- 

 duction of the disease under notice into Queensland waters. In New South Wales, as previously 

 stated, the oyster fisheries devastated belong entirely to riverine systems which have become much 

 altered in character and polluted by sedimentary deposits, through the clearance of their inland 

 water-sheds. The oyster-grounds of Moreton and Wide Bays, on the other hand, have such near 

 and free communication with the open ocean, that they are not influenced to anything approaching 



