K) CEYLON PEARL OYSTER REPORT. 



on the Gheval Paar, the catastrophes have been singularly few, and this is important 

 testimony to the reliability and relative safety of this region as a rearing ground, 

 provided it is kept supplied with the necessary young oysters. Omitting those 

 batches which probably died off from being left too long unfished, the only evidence 

 we have of catastrophic disappearances is as follows : 



(1.) Young oysters attached to weed in March, 1867, gone in December, 1868. 

 (Probably due to over wash of sand ; but the young spat when attached to 

 ' weed must always be very uncertain, and may simply have drifted out of 

 the area when the weed rotted or was detached by the next monsoon. 

 Mr. Hornell has suggested that these were " false spat " Avicula 

 vexillum.) 



(2.) The 2 to 3-year old oysters which were greatly diminished in number between 

 March, 1875, and March, 1876. (Probably eaten by carnivorous fishes, such 

 as Balistes.) 



(3.) The extensive beds of oysters 4 years old in November, 1887, which had nearly 

 all gone in February, but which are said to have been found further to the 

 east during the fishery. (This was no doubt due to currents during the 

 north-east monsoon,* as suggested by Sir William Twynam.) 



(4.) A few patches of small oysters found on East Gheval in 1898 had disappeared 

 in 1899. (Small patches may easily be missed; or the ravages of a few 

 Trygon-r&ys or a shoal of Balistes may so far reduce the patch that it is no 

 longer recognisable by a few chance dives. I think it unlikely that muddy 

 water caused by floods in the four rivers of the adjoining coast could, as 

 suggested by Sir W. Twynam, produce a serious effect so far out at sea. 

 The winter of 1898-9 was, however, an exceptional one, with heavy rains 

 and strong currents.) 



* This is corroborated by Captain Donnan, who lias kindly read the proofs of this section of the 

 Report for me, and who writes (July 22nd, 1904) : " I have no doubt whatever that a strong south-south- 

 east current was the cause of the loss of the splendid bed of oysters on the Cheval in 1888. I noticed 

 when I visited the bank in February to lift a sample and buoy oft' the bank, that the pieces of rock 

 brought up by the divers were covered with byssus, and the divers said no shells, broken or whole, were 

 to be found. I therefore concluded that the oysters must have been swept away by a current. I then 

 asked the man in charge of the " Active," which was on the paar from November as a guard boat, if he 

 had noticed any current after I left the banks in November, and he said, yes, in December when at 

 anchor on the bank he found the current so strong to the south that he was afraid the guard-boat would 

 drag her anchor, and he let go a second anchor he estimated the current to lie running at 4 knots and 

 said it lasted a week. During my inspection of the bank in February, the divers brought up a Pimm 

 shell with a number of old oysters on it, and so to try the eft'ect of a current, I had the shell towed 

 alongside the tug " Active," going at a speed of 4 knots. After about an hour's towing, and finding that 

 none of the oysters had dropped oft" the shell, I had the speed increased to about 5 or 5i knots, and in 

 about half an hour's time all the oysters had dropped oft', leaving their byssus on the Pinna ; so after that 

 experiment I had no doubt about, a current being the cause of the loss of oysters from the Cheval." 



