tyriical of the editile oysters. It grows singly, attached to rocks and corals which provide 

 sutistratuin for maiiy other foms. There was no eyidence of unusual mortality among any of 

 the Ijotton organisms living on pearl-oyster grotinds, and no mortality of fishes was ever 

 reriorted "hy the fishermen operating around Pearl Islands. Likewise, no unusual discolora^ 

 tion of vfater was noticed hy the inhaljitants of the islands or by the captains of tuna 

 fishing vessels working along the coast. 



Suspicion that waters around the Pearl Islands contained some mysterious poison 

 that killed pearl oysters must he abandoned as wholly unsuhstantiated. 



The sU£;gestion that some contagious disease destroyed a large percentage of 

 oysters a fe\i years ago cannot "be answered with certainty. I was unahle to find any 

 diseased or dying oysters. Only a few specimens were found which, judging hy the fact that 

 their valves v;ere still connected hy the hinge, had died a short time hefore. Unfortunately, 

 their tissues were completely decomposed or eaten hy crahs. 



Present observations show that the remaining oysters ai-e healthy and no\, Infected 

 hy parasites. It is, of course, impossible to infer from the observations made in I9US 

 v.'hat the condition of oysters was in 1937> vrhen their yield began to decline. 



Several considerations speak against the theory that contagious disease was the 

 cause of the decline of the fishery. Dead shells found on bottom were in various stages of 

 deterioration and fouling. If all of these oysters perished at the same time, there would 

 be no such difference in the state of erosion of their shells. Furthermore, rapid decline 

 of the pearl fishery, as shown by the records of export (Tig. 1) , began in I925, after the 

 production had reached more than 700,000 kilos per year. Assuming that the average weight 

 of an adult oyster of commerce is about 350 grans, the total nximber of live oysters re- 

 moved from the sea in this single year probabl^r was 2 million individuals. Intensive 

 fishing in the following decade may have prevented the rehabilitation of the grouiids, and 

 reduced the oyster population to a lower level. Interruption of export of nother-of-pearl 

 shells during the war years of 1939-19'^5 failed to bring rehabilitation of the grounds. 

 It is possible that some unknown adverse environmental conditions prevented recovery during 

 this period; but, on the other hand, one must bear in mind that interruption of export of 

 shells did not completely stop the fishing for oysters in search of pearls. 



Statistical data available at present record the total weight of shells shipped 

 from Panama. The number of oysters taken by individual fishermen in search of pearls 

 remains unrecorded. The figure is probably much less than the quantity of shells obtained 

 tr/ tte organized fishery, but even a small drain upon the oyster population might have been 

 si^ificant biologiceilly, especially in viev; of its already depleted state. 



Prom all of the facts presented and discussed in this report, I conclude that 

 overfishing v,-as the most probable cause of the depletion of the pearl-oyster grounds in 

 Panama. The decline of the fishery started after 1925j and, v;ith inconsequential partial 

 improvenents has continued until the present. We knov; from historical records that the 

 grounds near the Pearl Islands had been already depleted by the end of the l6th century, 

 when pearling operations by Spaniards vrere abandoned in favor of new and more productive 

 areas. The question is whether the population of pearl oysters may again restore itself if 

 given adequate protection. In view of the extremely small numbers of oysters remaining on 

 the grounds, it is impossible to give a categorical answer without a trial, but as long as 

 there are still a fe\^ living and healthy oysters, it airoears possible that the stock may be 

 at least partially rebuilt. 



The method of gathering of pearl oysters by divers inflicts no damage to the 

 grounds. Dredges, patent tongs, and similar gear used in harvesting edible oysters are 

 often destructive because of their excessive weight, and because the removal of shells or 

 other hard objects nakes the bottom unsuitable for the attachment of young oysters. In the 

 case of the pearl fishery, the physical condition of the bottom is not altered by Intensive 

 fishing. The only question, then, is whether the rate of reproduction of the few remaining 

 oysters will be sufficient to rehabilitate the grounds. Ho definite assujance that this 

 will be the case can be given at present. It is recommended, however, that efforts be made 

 to protect the remaining pearl oysters and to facilitate their propagation by the enactment 

 of the follov/ing measures: 



H7 



