Page:Popular Science Monthly Volume 63.djvu/237

Rh along with what we know of the past history of the bank as revealed by the inspectors' reports, shows that whenever young oysters are found on the Periya Paar, they ought, without delay, to be dredged up in the bulk and transplanted to suitable ground in the Cheval district—the region where the most reliable paars are placed.

From this example of the Periya Paar it is clear that in considering the vicissitudes of the pearl oyster banks, we have to deal with great natural causes which can not be removed, but which may to some extent be avoided, and that consequently, it is necessary to introduce large measures of cultivation and regulation in order to increase the adult population on the grounds, give greater constancy to the supply, and remove the disappointing fluctuations in the fishery.

There are in addition, however, various minor causes of failure of the fisheries, some of which we were able to investigate. The pearl oyster has many enemies, such as star-fishes, boring sponges which destroy the shell, boring molluscs which suck out the animal, internal protozoan and vermean parasites and carnivorous fishes, all of which cause some destruction and which may conspire on occasions to ruin a bed and change the prospects of a fishery. But in connection with such zoological enemies, it is necessary to bear in mind that from the fisheries point of view their influence is not wholly evil, as some of them are closely associated with pearl production in the oyster. One enemy (a Plectognathid fish) which doubtless devours many of the oysters, at the same time receives and passes on the parasite which leads to the production of pearls in others. The loss of some individuals is in that case a toll that we very willingly pay, and no one would advocate the extermination of that particular enemy.

In fact the oyster can probably cope well enough with its animate environment if not too recklessly decimated at the fisheries, and if man will only compensate to some extent for the damage he does by giving some attention to the breeding stock and 'spat,' and by transplanting when required the growing young from unsuitable ground to known and reliable 'paars.'

Those were the main considerations that impressed me during our work on the banks, and, therefore, the leading points in the conclusions given in my preliminary report (July, 1902) to the governor of Ceylon ran as follows:

 1. The oysters we met with seemed on the whole to be very healthy. 2. There is no evidence of any epidemic or of much disease of any kind.