OYSTERS AND OYSTER FISHERIES OF QUEENSLAND. 26 



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or less completely submerged, and over which there is a sufficient scour to prevent the 

 accumulation of sediment, old oyster shells or cultch constitute the most convenient and efficient 

 form of spat collector available. This material, however, if laid on muddy banks or where 

 there is an insufficient circulating stream, becomes speedily covered with slime and sediment, and 

 is, in such a condition, useless as a spat-trap. The sine qua iioii of successful oyster spat deposit, is 

 the existence of a perfectly clean surface for the embyro oysters to adhere to. On the oyster- 

 grounds in English waters, such as Whitstable and Heme Bay, where the natural beds consist 

 mainly of the old shells or cultch, the surface is continually worked over with the dredge, with 

 the express object of laying bare new and clean shell surfaces, for the attachment of the embryo 

 brood. 



The form of collector next demanding attention is that of fascines or faggots, composed of 

 boughs and branches of various sorts of timber trees. Collectors of this description are essentially 

 fitted for employment on oyster-grounds where they can be kept continually floating or submerged 

 below the surface of the water. The drawback to the use of fascines, or of tree branches in any 

 form, is their liability, on exposure to light, to become speedily coated with slimy vegetable growths 

 that leave no foothold for the young oysters. Considerable differences are, however, manifested by 

 distinct kinds of trees, with reference to their attraction for oyster spat. The commoner Australian 

 gums, Eucalypti, and wattles, Acacias, are apparently distasteful, on account of the pungency of the 

 essential oils and essences they continue to exude, even after prolonged submersion ; and they but 

 rarel}' become encrusted with oyster brood. The Coniferae, including the cedars and cypress- 

 pines and also the She-Oaks, or Casuarinas, have, on the other hand, been found in practice ■ 

 to yield more favourable results than any other timber, and that more especially in experiments 

 conducted by the author upon the artificial propagation of the Tasmanian oyster. The readiness 

 with which the Queensland species naturally adheres to the large branching aerial roots of the 

 orange mangrove, Rhizopliora miicrouata, would seem to indicate that this material would form 

 an excellent one for the systematic construction of fascines. 



To render fascines more efficacious as spat collectors, the boughs of which they are composed, 

 as used in Europe, are not unfrequently washed over with cement. This modified form of fascine 

 leads to those descriptions or collectors in which cemented surfaces are exclusively employed. The 

 most prominent of these are the cemented tiles first employed by M. Coste, by the aid of 

 which miles of barren mud flats on the coast of France have been converted into mines of wealth, 

 giving employment to thousands of individuals. Such collectors are eminently adapted, and were 

 originally constructed, for employment on banks or flats that are left uncovered at ebb-tide, and 

 they are totally unsuited for manipulation beneath the water. 



The peculiar advantage of cemented tiles, and of all forms of collectors constructed on the 

 same principle, consists in the fact that as the relatively large cemented superficies lie on the under 

 surface of the collector, the latter, when in position, remains almost permanently clean and ready 



