302 THE SEAS 



from being less hardy than the other, it cannot be reared 

 on the shore so easily, while it is subject to mysterious 

 diseases. 



Unlike the Portuguese oysters which are all either of 

 the male or female sex, the native oyster has the strange 

 property of being alternately one sex and then the other ; 

 the frequency of these changes depends on the temperature 

 of the water, for example on the Danish beds they do not 

 usually have more than one change of sex annually, but 

 on the French beds they may have two or three. Since 

 at each spawning the oyster in its female state produces 

 millions of young, the potential production of spat where 

 each oyster may spawn several times in a season, is almost 

 inconceivable. 



In Great Britain there is nothing to compare with the 

 French oyster industry. There are many beds dotted 

 along the coasts, of which the principal ones are situated 

 near Colchester ; everywhere the oysters live in shallow 

 water but are seldom uncovered in any number even at the 

 lowest spring tides. They are usually collected by small 

 rowing or sailing boats with the aid of iron dredges which are 

 dragged along the bottom, the oysters being collected in the 

 dredge bag which is usually made of steel links. Spat 

 collectors are seldom used, but during the summer it is 

 customary to throw great quantities of clean shell, known as 

 " cultch " over the beds so as to provide good settling 

 surfaces for the spat. Although the colder water round 

 the British coasts renders oyster cultivation a more difi&cult 

 problem than in France, there is no reason why the industry 

 should not be greatly developed ; a fact which is fortunately 

 recognized by the Ministry of Fisheries which has been 

 conducting experiments on the artificial rearing of oysters 

 at Conway, North Wales, for some years past. 



Oysters are also cultivated to some extent in Holland, 



