scEircity of young oysters (Fig. 23). less than 10 en. long, of v/hich only four were col- 

 lected. It is obvious that, being less conspicuous than the adults, they might have been 

 overlooked by the diver. It is, however, improbable that a person v;ith aany years of 

 exoerience and faniliar vfith the underwater conditions of Panana pearl grounds could have 

 overlooked nany snail oysters, es"oecially as he was specifically instructed to search for 

 them. The snail number of yo\ing indicates a very slow rate of propagation of the depleted 

 oyster riormlation. An inference can be nade that, tinder present conditions, many years 

 would be required to increase the population of pearl oysters sufficiently to support a 

 coi!TD.ercial fishery. 



Size and v;eight of shells 



The shells of ?inctada nazatlanica used in trade should be not less than 10 cm, 

 long, and of sufficient thickness to permit the cutting and polishing of its nacreous 

 layer. Old shells v/hich renain in the sea v/ater or on the beach for several weeks after the 

 death of the mollusk lose their lustre and are useless for the trade. Oysters of less than 

 10 c:n. in length na" be used by the industry if the shells are sufficiently thick. 



Since the shells are sold by weight, it is of interest to determine their length- 

 v^eidit relationshir). Tor the reasons stated above, only shells of live oysters, not damaged 

 by boring organisms, coijJLd be used for such a stud;r. These requirements reduced the mate- 

 rial available for weighing to 23 speci).iens. The freq.uencies of various length and weight 

 classes are shovm in Table 6. Oysters v/ith thick and heavy shells weighing from HOO to 500 

 grar.is vfere more numerous than those of anj' other class. This indicates that the present 

 ■oo-cnilation of pearl oysters consists prinaril;,^ of individuals several years old. Small 

 oysters less than U cm. in length v;ere absent. 



o 



Figure 23 Three yo-jng nearl oysters, Pinctada mazatlanica . Pearl 



Islands, Panaj.ia. 



37 



