ex-pect to iiave occurred if the v;ater v/ere poisoned 'by chemicals or 07 the red tide 

 (Galtsoff, 19^+9) • lTo'bod;y was ahle to state with certainty vj-here and when the mortality 

 of Tjearl oysters had started; and no'body coTild present any evidence of sus-picious Tiehavior 

 of Jananese fishermen on or neax the pearl grounds. 



My field o"bservations were planned to provide ansv/ers to some of these o.uestions. 

 They consisted of the follov;ingi (l) q.uaatitative sanrplings of pearl oysters to determine 

 their ahimdance on various grounds, (2) records of the temperature, salinity, and pH of 

 s^irface and 'bottom water, and tests for copper, (3) vertical sampling of plankton, 

 (U) ecologicail ohservatlons on pearl-oyster grovuids and adjacent hottoms, (5) microscopical 

 exaaination of oyster tissues with the view of finding whether the oysters were infected hy 

 microorganisms or v/ere diseased, and (6) ohservatlon on spavming of pearl oysters. 



This T3lan, with some modifications dictated hy circumstances, was cafried out, 

 although its execution sometimes was incomplete hecause of the lack of a trained assistant. 

 As far as was feasible, the material, collected at each station was examined alive, or was 

 preserved for more detailed eTajnins,tion in the laboratory. 



The vessel at my disposal, although of sufficient size (about SO feet long) 

 lacked an;";- space below the deck that could be made into a laboratory. .Conseq.uently all 

 microscopic and chemical work had to be done on deckt and all the instruments, materials, 

 and notes secured at the end of each observation and covered with canvas to protect them 

 from spray. 



Q.'uantitative sampling of pearl oysters was made by a professional diver using 

 regular diving equipment (scaphander and hand pump) » he was assisted by his crew of five. 

 The diving boat was tov/ed by the ChucuiJa and left at the places selected for diving. Record 

 v;as kept of all the oysters (dead or alive) found by the diver and of the time of diving. 

 The latter vgLried from 1 to ^ l/2 hours. It was fortunate that the Panamanian Government 

 v.'as able to secure for the expedition the sejrvices of Sr. Celedonio Pinzon, a diver of more 

 than 30 years experience. His familiarity with the pearl oyster grounds was very useful 

 In selecting representative locations for sampling stations and his intelligence and natural 

 curiosity were helpftil in collecting marine invertebrates associated with the pearl oyster 

 or inhabiting the pearl groxmds. 



At each station, shallow waters adjacent to the shore and the tidal flats or 

 rocks exposed at low tide were explored. Material was collected by using a small hand 

 dredge and by hand picking. Temperature of surface and bottom water was recorded to the 

 nearest tenth of a degree Centigrade, and the salinity was computed from hydrometer read- 

 ings nade aboard the ship. The pE of the v;ater was determined colorimetrically, using 

 Heilige discs and Cresol Red indicator. The readings v/ere corrected for salt error. 

 Plankton was collected v/ith Ho. 20 silk net 1 foot in diameter. Tissues of oysters and 

 plankton v/ere preserved in picro-formal solution (Bouin 3) or in 3 per cent formalin in sea 

 water. 



Invertebrates collected during the survey were examined in the laboratory of the 

 national Museum in Panama (Fig. ^) and shipT)ed to the United States for more detailed study. 

 It is regretted that part of the material obtained at the first eleven stations vra,s lost in 

 transit from Pearl Islands to Panama. A miscellaneous collection of Panamanian inverte- 

 brates comprising over 5tOOO specimens has been deposited in the U. S. National Museum in 

 Washington. A small number of Biyozoa incrusting mollusk shells was forv/arded for identi- 

 fication to Dr. R. C. Osborn, and upon completion of his studies v/ill be deposited with the 

 Allan Hancock Foundation of the University of Southern California in Los Angeles. 



ECOLOGICAL CHARACTERISTICS 07 PEARL OYSTER BOTTOMS AHD OP ADJACENT GROUltDS 



The range of distribution of the pearl oyster of Panama, Pinctada ( Margaritiphora ) 

 nazatlanica (Hanley) (Pig. 5) extends from the Gulf of California to the Gulf of Panama. 

 The species has been reported also from Galapagos and Peru. Throughout this wide range it 

 is found on hard or rocky bottoms. Adult specimens are from 5 to 7 inches in length. The 

 does not form continuous banks or beds typical of some of the species of the edible oysters 



11 



