In working auriferous river-beds, dredges have been used with considerable success in certain parts of New Zealand and on the Pacific slope in America.
The dredges used in California are almost exclusively of the endless-chain bucket or steam-shovel pattern.
Some dredges have a capacity under favourable conditions of over 2000 cub.
In South Island the river-beds of Otago province have been successfully worked by means of dredges, and good returns secured.
Limestone is abundant, and the city has various manufactures, including lime, foundry and machine-shop products, agricultural implements, planing-mill products, engines, steam shovels, dredges, pianos and silks.
The oyster fisheries give employment to over 56,000 fishermen, who man 4000 vessels, valued at $4,000,000, and 23,000 boats, valued at $1,470,000; the value of the 1 i,000 dredges and 37,000 tongs, rakes and other appliances used is $365,000.
It is the opinion of almost all who have studied the subject that any natural bed may in time be destroyed by overfishing (perhaps not by removing all the oysters, but by breaking up the colonies, and delivering over the territory which they once occupied to other kinds of animals), by burying the breeding oysters, by covering up the projections suitable for the reception of spat, and by breaking down, through the action of heavy dredges, the ridges which are especially fitted to be seats of the colonies.'