CURRENTS. 247 



Since the preceding report on the cui-rents prevalent in the gulf was ^vritten, 900 more drift 

 bottles have been liberated at the same stations durmg the south-west monsoon of 1911. 



The results are similar to those obtained in previous years, which they fuUy coi-roboratft. This 

 j'ear (1911), however, the monsoon was extraordinarily light, and the consequence was that the oceanic 

 current from the west was feeble, and never penetrated into the gulf at all. Consequently there was 

 no " head " of water in that region. The currents, therefore, ran to the north and through Paumbeu 

 Pass. On one occasion, when the monsoon was a little stronger than the year's average, this oceanic 

 cmTcnt, sweeping past Cape Comorin, caught a set of bottles liberated there. Passing in a south-easterly 

 dii-ection, it reached the Ceylon coast a little to the north of Colombo, where it caught and swept south- 

 ward a set of bottles liberated near Colombo. The interest of this fact is that bottles liberated off 

 Tallaivillu and Chilaw about the same time were drifted to the north. This interesting result shows 

 that the oceanic current Just reached Ceylon between Negombo and Colombo, and that only on one 

 occasion. 



The monsoon during July was very light and the current on both sides of the gulf, that is, off 

 Manapad cxnd Tutieorin on the Indian side, and off Colombo, Chilaw, and TallaiviUu on the Ceylon side. 

 During the early part of August the monsoon freshened a little, and on this occasion bottles released off 

 Cape Comorin were swept easterly by the monsoon ocean current, and were recovered on the south 

 coast of Ceylon between Colombo and Galle. During the second week in August the monsoon fell light 

 again, and the current off Cape Comorin and off Ceylon ran steadily north, imtil the monsoon finally died 

 away in September. 



Strictly speaking, there was practically no south-west monsoon during 1911. Consequently the 

 bottles ran generally north and were lost. Onty 23 per cent, were recovered, as against 51-5 per cent, 

 last year. Theoretically, dming a perfect south-west monsoon, bottles liberated on the stations shown 

 on the charts appended ought all to be recovered on the Ceylon coast. The strength of any south-west 

 monsoon may be measured by the percentage of bottles recovered. The weaker the monsoon , the greater 

 the percentage of bottles lost, and so with exotic larvae. 



Through the kindness of Captain Fysh, R.N.R., of the R.M.S. " Pahtaua," and Captain Dickinson 

 of the R.M.S. " Putiala," we were enabled to collect plankton twice daily (5 a.m. and 7 p.m.) over the 

 vicinity of the Tuticorm pearl banlis. A net was devised to take the collections whilst the ships were 

 under full way. The net consisted of a conical brass wire framework havuig a J-inch mesh. It 

 was made of woven brass wire, and was suitably weighted with a brass ring round the top. This frame- 

 work was intended to support the tow net when the ship was under way. Inside this net was fixed 

 and fitted a net of jute hessian to prevent the tow net proper from chafing against the brass. The tow net 

 itself was fitted and fixed inside the jute hessian. Splendid collections were made. The tow net had 

 to be renewed almost every day, but the jute hessian net usually lasted for thi-ee or four days. We 

 recommend this form of apparatus for collections of plankton imder similar circumstances. 



A few oyster larvse were noticed in the plankton on July 28 and 29 only, and these were scanty. 

 The experiment shows, however, that it is possible to obtain good plankton catches in this way, and 

 thus to know whether the oyster larvse wMch give rise to exotic spatfalls on our banks are present in 

 the vicinity of Southern India. 



The outstanding feature is however that, although oyster larvse may be present in enormous 

 numbers round Southern India, no exotic spat can possibly reach our banks unless the south-west 

 monsoon continues strong during the critical period. Tlie experiment during 1911 conclusively showed 

 that, even if larvse had been abimdant, they would have drifted through Paumben Pass and been lost. 

 Wlien oysters are present on the Tutieorin side, their larvse drift through Paumben Pass, or drop into the 

 abyss on their way to the pearl banks, or successfully reach the p ateau, depending absolutely on the 

 strength of the monsoon. 



As Steuart remarked, the factors controlling these natural events are at present bej'ond our control , 

 but now that the facts are understood, we recognize that the intermittency of fisheries is dependent on 

 the strength of the successive monsoons. We have often suspected that there were meteorological rhythm 



