OYSTEB-CULTUKE IN AUSTEALASIA. 565 



Ostrea glomerata, its most luxuriant development in New South 

 "Wales has been high up the river estuaries that so abundantly 

 intersect the coast-line. The Hunter, the Hawkesbury, and 

 the Clarence Eivers may be mentioned not only as the most 

 important of the oyster-growing areas, but also as those in 

 which the worm disease, or, as it may be more correctly termed, 

 the "mud disease," has been most prevalent. In my opinion 

 it is the altered conditions of these rivers, brought about mainly 

 through human agency, that has induced the diseased condition 

 of the oysters, their waters, in fact, being rendered more or less 

 incapable of supporting the mollusc in a healthy state. 



Through the clearance of the land and the establishment of 

 townships and settlements throughout the watersheds of these 

 rivers, the rainfall, which in former days fell upon and was 

 more completely absorbed by the primeval forests, is now 

 carried quickly away, and emptied by drains and culverts into 

 the watercourses communicating with the rivers. Simultane- 

 ously with this augmented discharge of water into the rivers a 

 vastly larger quantity of sediment is brought down, accom- 

 panied by a considerable percentage of organic and chemical 

 pollution that had no place in the composition of the water 

 under those conditions in which the oysters originally grew and 

 flourished. This greatly-augmented accession of flood- water, 

 with its accompaniment of sediment and chemical pollution, 

 cannot exert other than a very deleterious influence upon the 

 river oyster-fisheries. 



A case in point, in which the oysters, formerly growing 

 abundantly many miles up a river's course, have been gradually 

 pushed further and further down towards the sea through the 

 agencies just described, fell under my personal observation in 

 Tasmania. In the Eiver Tamar, debouching on the northern 

 coast-line of that colony, the mud-oyster (Ostrea edidis) was 

 originally abundant from the Heads half-way to the town 

 of Launceston, some forty miles distant. By degrees — as 

 testified to by residents of the district — the oysters have 

 disappeared from the formerly prolific higher portions of 

 that river, known as Whirlpool Eeacli 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 contain- 

 ing an insufficient amount of saline ingredients, organic pollu- 

 tion from the town 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 remnant gathered there were in a decidedly un- 



