Manihiki island is located at 10.25'23"W, 161.02'10"S and forms part of the northern group. The island is crudely oval in outline and the greatest width of the reef appears to be about 0.6km. The greatest depth of the lagoon is approximately 90m.

There are no navigable passages through the reef and only a few, barely discernable, channels through which small boats must be walked at low tide. Lagoon-ocean water interchange can come only from percolation through the reef wall and over the reef with water level changes. Water movement into and out of the lagoon and over the reef is greatest at the northwest corner and along the southern flank of the atoll. The lagoon proper contains 34 named patch reefs (motus, pinnacles to surface, bommy to surface) and perhaps twice as many unnamed. Several of the former have homes and pearl processing establishments built on and covering their tops. The lagoon surface covers approximately 45 square km.

The land is concentrated in a 9 km strip called Ngake along the northeastern side and a 4.25km strip called Tauhunu along the western side of the atoll. In total there is a population of 468 people. The oldest of two villages, Tukao, is at the north end of Ngake. The largest village, 6km SW of Tukao, is Tauhunu on Tauhunu Motu. It is the main port for the atoll. There are no bridges or causeways linking the motus thus travel by boat is necessary. The bulk of the land is covered with coconut trees, saltbush, pandanus etc. and is uninhabited though every centimetre is owned by somebody.

The principal income earner on Manihiki is the black pearl. At a national scale the pearl culture industry at Manihiki must rate as one of the Cook Islands highest valued growth economic sectors. In May 1999 the Ministry of Marine Resources conducted a survey of cultured pearl farms in Manihiki. It was estimated that approximately 1.5 million adult cultured pearls are stocked in the lagoon. The annual production of this amount of pearl oysters is estimated to be in the order of NZ$10 million dollars, or 250 thousand pearls. An upward trend suggests that by the year 2003 there will be 2 million cultured oysters and an annual production of NZ$18 million dollars.

The May 1999 survey was undertaken to assess the numbers and categories of oyster stocks and determine the sizes of the farms and establish maps of their boundaries. The lagoon can only support so many pearl oysters before problems begin occurring, so information of this nature is fundamental to proper management of Manihiki lagoon. Problems could include a decrease in the quality of the water, and subsequently a decrease in the quality of the pearls themselves.

The total area claimed by the 111 pearl farms surveyed is 7.73 square kilometers, or approximately 30% of the area that could be potentially farmed in Manihiki (i.e. the area of lagoon between 10 to 30 meters deep). Results of this survey suggest that if space is properly managed in the lagoon then levels of 2 million cultivated oysters could be attained without serious threats to the health of the oyster. Growth trials conducted throughout the lagoon have reported lower shell growth rates at highly stocked pearl farms, so to go above the 2 million level may cause problems for all the farms.

Rakahanga and Manihiki have close ties. Formerly the same group of people lived on both Manihiki and Rakahanga and they migrated between the two islands. This changed in 1852 after the missionaries arrived. Rakahanga is only 42 km north of Manihiki. It consists of two major islands and a host of smaller motu almost completely enclosing a central lagoon about 4km long and 2km wide at its widest points. Copra is the only export product although the islanders grow breadfruit and a taro-like vegetable. The population is concentrated in the village of Nivano on the south-west corner of the atoll.

The role of the Ministry of Marine Resources

There are MMR personnel in Manihiki. They are mainly concerned with the pearl industry side of marine issues. They keep an eye on the growth of the pearl farms and take water samples for quality analysis back in Rarotonga. As with the other offices, household surveys of seafood consumption are part of their scope. They are also answerable to requests made by the Island Council of Manihiki.

The MMR personnel on Rakahanga carry out similar duties, however in Rakahanga there are no pearl farms. Ideally they will help encourage the spread of pearl farming from Manihiki to Rakahanga. The Rakahanga lagoon is suitable for pearl farming and has close ties with Manihiki, and therefore it is expected that pearl farming will occur there in the near future.