Natural History of the Whanganui River and Whanganui National Park
The land surrounding the Whanganui River is only about one million years old. Formed of soft sandstone and mudstone (papa) from the ocean-bed, it has been eroded by water to form sharp ridges, deep gorges, sheer papa cliffs and waterfalls.
Over this land has grown a broadleaf-podocarp forest of rata, rewarewa, rimu, tawa, kamahi and kowhai with beech dominant on the ridge tops. Tree ferns and plants that cling to the steep riverbanks are very distinctive.
Bird species such as kereru (native pigeon), tiwaiwaka (fantail), tui, toutouwai (robin), riroriro (grey warbler) and miromiro (tomtit) are often seen and heard. The call of the brown kiwi can often be heard at night.
The Whanganui River is rich in eels, lamprey, species of galaxiid (a group of native fish species including whitebait and kokopu), koura (freshwater crayfish) and black flounder.-Source: Department of Conservation website.
From Taumarunui to Whakahoro, much of the river margin has been converted to farmland, but there are still some good-sized pockets of bush. Often it is hard to tell that there is a road not far from the river. One of the features of the Retaruke River is the many fossilised rocks and it is home to the rare blue duck (whio).
Below Whakahoro and through to Kahura Station, much of the park is unmodified rainforest – untouched by humans that is, but goats, deer, pigs and possums provide a major challenge for DOC in its battle to maintain the biodiversity.
Kiwi can often be heard calling at both John Coull Hut and the Ramanui Campsite, while long-tail native bats can also be seen flying at dusk at the John Coull Hut. There are glowworms at both John Coull Hut and the Bridge to Nowhere Lodge.
As well as the native fish in the river, there are both brown and rainbow trout, which can be caught with the appropriate licence. Most success comes from trolling a spinner behind your canoe.