CURRENTS. 239 



It is only when a strong moiisoon persists for some considerable time that the oceanic current 

 penetrates far enough into the gulf to sweep the Tuticoriu beds. In that case the easterly current stretching 

 across the gulf reaches the Ceylon coast well north of Tallaivillu Point, carrying with it sp.^t when 

 present from the Indian side. Such spat appear to be dejiosited on the banks under lease, and to 

 never reach the banks further south, as the distance in the latter case is too great (HO miles), and 

 the larvse mature and sink long before the current reaches so far south. 



The pearl banks under lease which are situated in that beautifully i)rotectcd cul-de-sac at the 

 extreme north-east of the gulf now call for particidar attention. Their productivity at times is marvellous, 

 yet barren years intervene. Much of the barrenness is due to causes other than currents, but, on the 

 other hand, it is quite certain that much of their productiveness is, a!id has been, due to the fact that 

 they have been periodically stocked with exotic sjiat, which, added to their own inherent powers of 

 production and recuperation, has more than amply satisfied the demands of rapacious men and predatory 

 fish. They also owe much to their protected position, and a glance at the chart will serve to illustrate 

 this fact. 



The only surface movements on this part of the plateau are entirely dependent on the wind. 

 Except in very strong and prolonged south-west monsoon no real current exists, and the tendency is for 

 spat liberated in the vicinity to be retamed thereon , and to be deposited near its source of origin. If strong 

 monsoon persists, we have seen that the current penetrates further and further into the gulf until it 

 sweeps the Tuticorin beds, and the possibilities are then tjresent for spat being brought across and 

 deposited on the banks under lease. The same current turning south and following the trend of the 

 land would also carry away to the south the local spat from the banks imder lease, but the likelihood is 

 that such spat, instead of actually being deposited on the banks still under control, would merely drift 

 ashore. On the more inshore areas, as on the Kondatchi Paar, succeeding spatfalls have gradually 

 wandered closer iiifihore. The possibilities of the banks under lease receiving spat from the Indian side 

 during a strong monsoon are very considerable, althougli as yet we only understand in merest outline 

 a few of the factors which may conduce to bring about this result. 



If the south-west monsoon is Ught or moderate, the spat from the Indian side runs with the northern 

 current through the Paumben Pass. It is evident that under these conditions no spat could possibly 

 drift on to the banks under lease. It is only when the south-west monsoon is very strong and prolonged 

 that the oceanic current penetrates further and further into the gulf, until eventuaUy it sweeps the 

 Tuticorin banks. If oysters are present there, their spat is almost certainly brought across to the banks 

 under lease by the current, which in strong monsoon most probably penetrates the gulf much further 

 north than is indicated on the appended chart showing the residts obtained during 1910, when the 

 monsoon was not either veiy strong or continuous. The absence of an exotic spatfall this year, as in 

 other years, lias either been due to the moderate monsoon which prevailed, or to the absence of spatting 

 oysters on the Tuticorin banks. 



The larvte of the oyster are pelagic, i.e., they live on the surface of the ocean for about the first 

 five to seven days of their existence. They then develop a shell, and droi^ping tp tlie bottom become 

 attached. There can be no doubt tliat many drop in deep water and are lost. The depth most suitable 

 for oysters is 6 fathoms. 



The distance from the Indian banks to the banks under lease is approximately 85 mdes. Taking 

 seven days as the maximum time occupied by the pelagic stage, a continuous surface drift to the east 

 of 0-6 knot per hour for six successive days would place the spat on our banks. Wo boheve that this 

 does hajjpen occasionally, but only during strong monsoon. Otherwise it would bo impossible to explain 

 the -sudden transition from absolute barreimess to remarkable luxuriance which has characterized the 

 area under lease through long periods of histoiy. 



Such in merest outhne are the conditions of the surface current over the entire plateau. No 

 doubt there are other factors atM-ork, which subsequent research alone can elucidate, but wo feel satisfied 

 that the results and explanations given above have a very real significance, and that the broad general 

 facts are as above stated. Although our results this year distinctly prove that the oceanic current 

 reaches tlic Ceylon coast south of Tallaivillu Point during strong monsoon weather, the results of another 



