30 SPOLIA ZEYLANICA. 



BIOLOGICAL SURVEY OF TRINCOMALEE HARBOUR. 



By Joseph Pearson. 



(With four Charts.) 



TN January, 1911, I paid a visit to Trincomalee, where I spent 

 -■- some ten days in surveying the inner harbour with dredges and 

 by means of divers. This work appeared to me necessary, seeing 

 that so many suggestions have been made in recent years regarding 

 the estabhshment of pearl oyster, sponge, and mother-of-pearl oyster 

 fisheries at Trincomalee. 



The ha.rbour is admirably protected from both monsoons 

 and possesses a rich fauna, but neither the pearl oyster nor the 

 commercial sponge thrives. In 1857 Kelaart planted pearl oysters 

 in the bay, but conditions do not appear to have been favourable. 

 Herdman, in 1902, obtained several young oysters and under-sized 

 adults. He noted the low salinity of the water and the small amount 

 of plankton, and concluded that, " while experiments might be 

 carried on at Trincomalee when impossible elsewhere because of 

 weather, the conditions of water and food are probably not so favour- 

 able as in the Gulf of Mannar , and would probably not lead to such 

 active growth and shell (including pearl) formation." During my 

 visit I obtained very few pearl oysters, even in those parts of the 

 harbour where conditions are most favourable, and where, therefore, 

 one would naturally expect to find them. All the collected evidence 

 appears to point to the fact that the conditions in Trincomalee 

 harbour are unfavourable to the pearl oyster. On the pearl banks 

 the oyster thrives best in depths between 5 and 8 fathoms, and 

 a hard bottom is essential. The area in Trincomalee harbour in 

 which botli these conditions are fulfilled is very small. At the 

 north-east end of the harbour there is a considerable area within 

 the 5-fathom line having a hard bottom. This area is probably 

 too shallow for the successful cultivation of adult oysters, but it is 

 conceivable that an oyster nursery might meet with some success. 

 But the idea of having a nursery so far from the pearl banks does not 

 seem to be practicable, as oyster transplantation of any magnitude 

 would probably be attended by great mortality. 



Professor Herdman suggested the possibility of a future sponge 

 fishery at Trincomalee. The commercial sponge is at present a rare 

 member of the fauna of the harbour, and its present distribution 

 very limited. Out of about sixty stations at which dredgings were 

 taken in January the commercial sponge was only present at one or 



