The “sadof” is more scattered and less numerous than the “bulbul”; and in order to save much useless diving, it is customary to inspect the bottom before descending. Therefore, operations are largely restricted to calm weather, when the water is sufficiently clear to enable the divers to sight the individual oysters on the bottom. In recent years, water-telescopes have been used to assist in locating them. The most popular form consists of a tin can with a sheet of glass inserted in the bottom. The glazed end of the tin is submerged several inches below the surface, affording a far-reaching and much clearer vision. In this fishery the divers work from small canoes (_uri_), each manned by two men, one of whom rows while the other leans over the bow and searches for the oysters. When one is sighted, he dives into the water for it, and then returns to the boat to resume the search. The pearling season begins commonly in March or April, and continues until about the end of May; it is renewed in the autumn, continuing through September and October.[167] The vessels employed are of two varieties: _dhows_ carrying from twenty to eighty men each, and the much smaller _sambuks_ or sail-boats without decks, each with from six to twenty-five men, most of whom are Negro slaves. Many of the large vessels are from the Persian Gulf. The _sambuks_ are owned principally by Zobeid Bedouins inhabiting the coast between Jiddah and Yambo, and also the islands near the southern end of the sea, which are very hot-beds of pearls, shells, religious frenzy and half famished Arabs and Negro slaves. The “bulbul” oysters are taken in nearly the same manner as in the Persian Gulf. When the vessel is located over the reef, each diver descends, commonly with a short stick of iron or hard wood, with which he releases the oysters within reach; placing them in a sack, he is pulled up by an attendant when his breath is nearly exhausted. The fisheries are prosecuted along both sides of the Red Sea and in the channels among the islands, from the Gulf of Akabah to Bab-el-Mandeb. They are especially extensive among the Dahlak Islands on the coast of the Italian colony Eritrea, where the population is largely supported by them. This was the center of the industry during the time of the Ptolemies and in the early Christian era. The fisheries are also important in the vicinity of Jiddah, the port of entrance for Mecca and Medina, holiest places of Islam. They likewise exist near Kosseir at the northern end of the sea, and at Suakin, Massawa, the Farsan Islands, and Loheia, near the lower end. They are carried on by Arabs, who succeed in evading efforts at control on the part of the local governments. Even on the African side, the Arab fishermen predominate, for the native Egyptian has never evinced much fondness for venturing on the sea.