Oysters belonging to two species viz., Crassostrea cucullata and Ostrea sp. occur in moderate numbers, though not in commercial quantities, on intertidal rocks in Sector 1 (Fig. 10). They are present in much lesser numbers in Sectors 4, 5, 6 and 8 also (Pig. 2). Majority of the specimens of C. cucullata, which is the preferred species, had not attained commercial size of about 70–80 mm length. It is of interest to note that the maximum settlement of oyster is seen in Sector 2,where barnacles occur in negligible numbers only. In the other sectors oysters are seen among heavy settlements of barnacles of genus Balanus (Fig. 11). There is no evidence of changes in seasonal succession of oysters and barnacles. Many dead oysters were encountered in Sector 1 and the reasons for the same are not know.
Length measurements of C. cucullata were taken in selected areas during April 1973, with a view to gather information on the alee distribution of living adult oysters (Table VII). Rocks occurring in approximately 5 m2 area of intertidal region were taken into consideration for this purpose. Juveniles and spat were excluded. Oysters measuring more than 65 cm in length were found to be mostly dead. In approximately 60 percent of the specimens dissected for separate studies, the meat condition was moderately satisfactory, with greyish white colouration.
Table 7
LENGTH MEASUREMENTS OF C. CUCULLATA
| Length range mm | Number of specimens | ||
| South east of Aqaba Hotel | Near Palm Beach Hotel | South of Palm Beach Hotel | |
| 11–15 | - | 3 | - |
| 16–20 | - | - | - |
| 21–25 | 1 | 2 | - |
| 26–30 | 7 | 4 | 1 |
| 31–35 | 8 | 3 | 2 |
| 36–40 | 12 | - | 6 |
| 41–45 | 14 | 1 | 4 |
| 46–50 | 2 | - | 4 |
| 51–55 | 2 | - | 5 |
| 56–60 | 1 | - | 1 |
| 61–65 | - | - | 2 |
Length measurements of naturally occurring oysters on a fixed cement structure in Sector 1 were taken on 1 April, 30 April and 30 May 1973, with a view to observe the rate of growth. The data obtained are summarized in Table 8.
Table 8
LENGTH OF OYSTERS ON A FIXED STRUCTURE
| Length range mm | Number of specimens | ||
| on 1.4.73 | on 30.4.73 | on 30.5.73 | |
| 30–35 | 2 | - | - |
| 36–40 | 3 | 4 | 3 |
| 41–45 | 8 | 6 | 4 |
| 46–50 | 5 | 6 | 5 |
| 51–55 | 4 | 5 | 6 |
| 56–60 | 2 | 3 | 5 |
| 61–65 | 2 | 2 | 2 |
| 66–70 | 3 | 2 | 2 |
| 71–75 | 1 | 1 | 2 |
| 76–80 | - | 1 | 1 |
The mean lengths recorded were:
| on | 1.4.73 | - | 50.43 mm |
| 30.4.73 | - | 54.32 mm | |
| 30.5.73 | - | 57.65 mm |
Rate of growth of selected oysters growing on small stones was studied by keeping them in Test pit No. 1 . Similar observations were attempted in Test pit No. 2 also, but the oysters did not survive here due to fresh water conditions in the pit during low tide regimes Ten oysters in length groups 36–40 mm and 41–45 ran were selected for trials in each pit. On the basis of final measurements taken in Pit No. 1, average rate of growth was found to be 3.1 mm per month.
With a view to study the nature and intensity of oyster spat settlement, nylon strings with drilled oyster and scallop shells, and corrugated asbestos sheets of surface area 1 500 cm2 (both sides) were either suspended or kept fixed to firm structures in the intertidal region of Sectors 1, 3 and 4 (fig. 1, 2 & 13). Strings of scallop shells and two asbestos sheets fixed to an old jetty in Sector 3 were lost after three weeks due to unusually heavy seas.
Spatfall was observed in most cases and counts were taken at the end of one month periods (except in Sector 3 where the materials were lost). Maximum spat settlement was observed on the asbestos sheets fixed firmly on the vertical structures of an old boat lying at the intertidal region in Sector 1 (Fig. 14).
The average intensity of spat settlement observed was as follows:
| April | May | ||||||
| Sector | 1 | - | On oyster shell strings | - | 2.5 per shell | 0.5 per shell | |
| On asbestos sheets - | |||||||
| fixed | - | 12 per 100 cm | 4 per 100 cm2 | ||||
| suspended | - | 2 " | 1 " | ||||
| Sector | 4 | - | On asbestos sheets - | ||||
| fixed | - | 3 " | 1 " | ||||
It is particularly significant that the maximum spat settlement occurred in Sector 1, and this matter needs further investigation.
General observations on the size of naturally occurring spat and early juvenile oysters in the different sectors indicated that most probably the spatfall must have occurred four to five months earlier, i.e. during early winter. This will have to be confirmed by future seasonal observations.
