Cook Strait () is a strait that separates the North and South Islands of New Zealand. The strait connects the Tasman Sea on the northwest with the South Pacific Ocean on the southeast. It is wide at its narrowest point,McLintock, A. H., ed. (1966) Cook Strait from An Encyclopaedia of New Zealand, updated 18-Sep-2007. Note: This is the distance between the North Island and Arapaoa Island; some sources give a slightly larger reading of around , that between the North Island and the South Island. and has been described as "one of the most dangerous and unpredictable waters in the world".McLauchlan, Gordon (ed.) (1987) New Zealand encyclopedia, Bateman, P. 121. . Regular ferry services run across the strait between Picton in the Marlborough Sounds and Wellington.
The strait is named after James Cook, the first European commander to sail through it, in 1770., p. 99. The waters of Cook Strait are dominated by strong tidal flows. The tidal flow through Cook Strait is unusual in that the tidal elevation at the ends of the strait are almost exactly out of phase with one another, so high water on one side meets low water on the other. A number of ships have been wrecked in Cook Strait with significant loss of life, such as the Maria in 1851,Disasters and Mishaps – Shipwrecks, from An Encyclopaedia of New Zealand, edited by A. H. McLintock, originally published in 1966, updated 2007-09-18. the City of Dunedin in 1865,Steamer 'City of Dunedin' – Mysterious Sinking . the St Vincent in 1869, the Lastingham in 1884, in 1909SS Penguin wrecked in Cook Strait – 12 February 1909. New Zealand History Online, Ministry for Culture and Heritage. Updated: 6 Oct 2020. and in 1968.
History
In Māori legend, Cook Strait was discovered by Kupe the navigator. Kupe followed in his canoe a monstrous octopus called Te Wheke-a-Muturangi across Cook Strait and destroyed it in Tory Channel or at Pātea.
When Dutch explorer Abel Tasman first saw New Zealand in 1642, he thought Cook Strait was a bight closed to the east. He named it Zeehaen's Bight, after the Zeehaen, one of the two ships in his expedition. In 1769 James Cook established that it was a strait, which formed a navigable waterway.
Cook Strait attracted European settlers in the early 19th century. Because of its use as a whale migration route, whalers established bases in the Marlborough Sounds, based out of Tory Channel and Port Underwood, and also in the Kāpiti area.McNab, Robert (1913). A History of Southern New Zealand from 1830 to 1840. Whitcombe and Tombs Limited. ASIN B000881KT4.Martin, Stephen (2001). The Whales' Journey: Chapter 4: The northerly migration. Allen & Unwin. . From the late 1820s until the mid-1960s Arapaoa Island was a base for whaling in the Sounds. Perano Head on the east coast of the island was the principal whaling station for the area from 1911. The houses built by the Perano family are now operated as tourist accommodation.Perano Homestead.
During the 1820s Te Rauparaha led a Māori migration to, and the conquest and settlement of, the Cook Strait region. In 1822 Ngāti Toa migrated to Cook Strait region, led by Te Rauparaha.
From 1840 more permanent settlements sprang up, first at Wellington, then at Nelson and at Whanganui (Petre). At this period the settlers saw Cook Strait in a broader sense than today's ferry-oriented New Zealanders: for them the strait stretched from Taranaki to Cape Campbell, so these early towns all clustered around "Cook Strait" (or "Cook's Strait", in the pre-Geographic Board usage of the times) as the central feature and central waterway of the new colony.
Between 1888 and 1912 a Risso's dolphin named Pelorus Jack became famous for meeting and escorting ships around Cook Strait. Pelorus Jack was usually spotted in Admiralty Bay between Cape Francis and Collinet Point, near French Pass, a channel used by ships travelling between Wellington and Nelson. Pelorus Jack is also remembered after he was the subject of a failed assassination attempt. He was later protected by a 1904 New Zealand law.
At times when New Zealand feared invasion, various coastal fortifications were constructed to defend Cook Strait. During the Second World War, two gun installations were constructed on Wrights Hill behind Wellington. These guns could range across Cook Strait. In addition thirteen gun installations were constructed around Wellington, along the Mākara coast, and at entrances to the Marlborough Sounds. The remains of most of these fortifications can still be seen.
The Pencarrow Head Lighthouse at the entrance from Cook Strait to Wellington Harbour was the first permanent lighthouse built in New Zealand. Its first keeper, Mary Jane Bennett, was the only female lighthouse keeper in New Zealand's history. The light was decommissioned in 1935 when it was replaced by the Baring Head Lighthouse.
Geography
Approximately 18,000 years ago during the Last Glacial Maximum when sea levels were over lower than present day levels, Cook Strait was a deep harbour of the Pacific Ocean, disconnected from the Tasman Sea by the vast coastal plains which formed at the South Taranaki Bight which connected the North and South islands. Sea levels began to rise 7,000 years ago, eventually separating the islands and linking Cook Strait to the Tasman Sea.
The strait runs in a general NW-SE direction, with the South Island on the west side and North Island on the east. At its narrowest point, separate Cape Terawhiti in the North Island from Perano Head on Arapaoa Island in the Marlborough Sounds. Perano Head is actually further north than Cape Terawhiti. In good weather one can see clearly across the strait.
The west (South Island) coast runs along Cloudy Bay and past the islands and entrances to the Marlborough Sounds. The east (North Island) coast runs along Palliser Bay, crosses the entrance to Wellington Harbour, past some Wellington suburbs and continues another to Mākara Beach.
The Brothers is a group of tiny islands in Cook Strait off the east coast of Arapaoa Island. North Brother island in this small chain is a sanctuary for the rare Brothers Island tuatara, while the largest of the islands is the site of the Brothers Island Lighthouse.The shores of Cook Strait on both sides are mostly composed of steep cliffs. The beaches of Cloudy Bay, Clifford Bay, and Palliser Bay shoal gently down to , where there is a more or less extensive submarine plateau. The rest of the bottom topography is complex. To the east is the Cook Strait Canyon with steep walls descending eastwards into the bathyal depths of the Hikurangi Trough. To the north-west lies the Narrows Basin, where water is deep. Fisherman's Rock in the north end of the Narrows Basin rises to within a few metres of low tide, and is marked by waves breaking in rough weather. A relatively shallow submarine valley lies across the northern end of the Marlborough Sounds. The bottom topography is particularly irregular around the coast of the South Island where the presence of islands, underwater rocks, and the entrances to the sounds, create violent eddies. The strait has an average depth of .
In 1855 a severe earthquake occurred on both sides of Cook Strait. In 2013 two large earthquakes measuring 6.5 and 6.6 on the Richter Scale struck Cook Strait, causing significant damage in the town of Seddon, with minor to moderate damage in Wellington.
Oceanography
The waters of Cook Strait are dominated by strong tidal flows. The tidal flow through Cook Strait is unusual in that the tidal elevation at the ends of the strait are almost exactly out of phase with one another, so high water on one side meets low water on the other.Lunar Semidiurnal Tide (M2). NIWA. Accessed 21 November 2020. This is because the main M2 lunar tide component that happens about twice per day (actually 12.42 hours) circulates anti-clockwise around New Zealand, and is out of phase at each end of the strait (see animation on the right). On the Pacific Ocean side the high tide occurs five hours before it occurs at the Tasman Sea side. On one side is high tide and on the other is low tide. The difference in sea level can drive tidal currents up to 2.5 metres per second (5 knots) across Cook Strait.Stevens, Craig and Chiswell, Stephen. Ocean currents and tides: Tides. Te Ara: The Encyclopedia of New Zealand, updated 21 September 2007.
There are numerous computer models of the tidal flow through Cook Strait. While the tidal components are readily realisable, the residual flow is more difficult to model.Bowman, M. J., A. C. Kibblewhite, R. Murtagh, S. M. Chiswell and B. G. Sanderson (1983) Circulation and mixing in greater Cook Strait, New Zealand. Oceanologica Acta 6(4): 383–391. Probably the most prolific oceanographer to research the strait was Ron Heath based at the N.Z. Oceanographic Institute. He produced a number of studies including analysis of tides Heath, R. A., 1978. Semi‐diurnal tides in Cook Strait. New Zealand Journal of Marine and Freshwater Research, 12(2), pp. 87–97. which identified the presence of a "virtual amphidrome" in the region. Heath also quantified a best estimate for the time of the "residual current" (i.e. net current after averaging out the tidal influence) in the strait.Heath, R. A., 1986. In which direction is the mean flow through Cook Strait, New Zealand—evidence of 1 to 4 week variability?. New Zealand journal of marine and freshwater research, 20(1), pp. 119–137. This continues to be a topic of research with computer simulations combining with large datasets to refine the estimate.Hadfield, M. G. and Stevens, C. L., 2021. A modelling synthesis of the volume flux through Cook Strait. New Zealand Journal of Marine and Freshwater Research, 55(1), pp. 65–93.
Despite the strong currents, there is almost zero tidal height change in the centre of the strait. Instead of the tidal surge flowing in one direction for six hours and then in the reverse direction for six hours, a particular surge might last eight or ten hours with the reverse surge enfeebled. In especially boisterous weather conditions the reverse surge can be negated, and the flow can remain in the same direction through three surge periods and longer. This is indicated on marine charts for the region. Furthermore, the submarine ridges running off from the coast complicate the ocean flow and turbulence.Stevens, C. L., M. J. Smith, B. Grant, C. L. Stewart, T. Divett, 2012, Tidal Stream Energy Extraction in a Large Deep Strait: the Karori Rip, Cook Strait, Continental Shelf Research, 33: 100–109. . The substantial levels of turbulence have been compared to that observed in the Straits of Gibraltar and Seymour Narrows in British Columbia.Stevens, C. L., 2018. Turbulent length scales in a fast-flowing, weakly stratified, strait: Cook Strait, New Zealand. Ocean Science, 14(4), pp. 801–812. .
Marine life Cook Strait is an important habitat for many cetacean species. Several dolphins (bottlenose, common, dusky) frequent the area along with killer whales and the endemic Hector's dolphins. Long-finned pilot whales often strand en masse at Golden Bay. The famous Pelorus Jack was a Risso's dolphin being observed escorting the ships between 1888 and 1912, though this species is not a common visitor to the New Zealand's waters. Large migratory whales attracted many whalers to the area in the winter. Currently, an annual survey of counting humpback whales is taken by Department of Conservation and former whalers help DOC to spot animals by using several vantage points along the strait such as on Stephens Island. Other occasional visitors include southern right whales, blue whales, sei whales and sperm whales. Giant squid specimens have been washed ashore around Cook Strait or found in the stomachs of sperm whales off Kaikōura.