OBYLON PEARL BANKS/ 209 



with the work. But although the ten years' work has made the task 

 much hghter, the mam problem is still unsolved, as the present 

 barren conditions of the banks only too plainly testifies. Moreover, 

 the combined results of the ten years' operations are not convincing 

 enough to induce the writer to agree with Mr. Southwell that, 

 "given a spatfall, only thorough inspection, care, and normal 

 foresight in isolatmg breeding stocks, &c., are required to make 

 the banks perennially productive." Mr. Southwell is too optimistic 

 when he thinks the future presents such an easy task, and he is 

 perhaps too sanguine when he records his belief that a spatfall is 

 almost certain to take place at an early date. 



Herdman's Summary and Recommendations. 



Herdman considered that the principal causes of mortality were 

 (1) silting sand, (2) predaceous fish, (3) overcrowding, (4) over- 

 fishing, (5) various other causes, such as disease and attacks of 

 invertebrates. 



Amongst other things, he recommended transplanting, cultching 

 of sandy areas, the institution of drift-bottle experiments. 



It is instructive to determine how far the various practices 

 advocated by Herdman have been seriously tested. 



The question of silting sand on the banks is discussed elsewhere. 

 If this danger is a real one, it would appear difficult to overcome, 

 except by transplanting the oysters from places where large sandy 

 stretches predominate. Southwell and Kerkham have not fully 

 appreciated Herdman's point in regard to the dangers of silting sand. 

 They have written a great deal to show that the movement of the 

 bottom water is vertical and not horizontal, but one is not convinced 

 that this vertical movement, if admitted, may not give rise to 

 silting. So long as silting takes place, from whatsoever cause, the 

 precautions suggested by Herdman must be practised. 



There appears to be universal agreement that predatory fish are 

 an imjDortant source of danger, but our knowledge on this subject 

 is not a little vague since the pubhshed information is extremely 

 meagre. It would have been helpful if exact records had been kept 

 of the thousands of trawling operations which have been conducted 

 throughout the course of the ten years' inquiry. One may be 

 forgiven for emphasizing once more the importance of a detailed and 

 systematic collection of data in the course of a big investigation 

 extending over many years, such as the one under discussion. It 

 is by such methods that results of joermanent value may best be 

 attained. In regard to the natural enemies of the oyster, the 

 problem would have been a much simpler one for future workers if 

 detailed records of the gut-contents of fishes had been available. It 

 would also have been of interest to have had a comparison of the fish 

 fauna of the banks during fishery years and non-fishery years, to have 

 determined whether the fish which feed on oysters disappear when the 



