New Zealand grayling

The New Zealand grayling ("Prototroctes oxyrhnchus)" is an extinct species of fish which was endemic to New Zealand. The New Zealand grayling, was known by the Māori people by many names including pokororo, paneroro, kanae-kura, however, the most common being Upokororo. The variety of names for the fish came from either other tribes or to describe the fish at different periods of its life cycle. Even though this fish is named grayling, it is not related to European or American graylings and lacks the large dorsal fin ‘typical’ graylings are characterised by. The New Zealand grayling was an amphidromous species, migrating between freshwater and saltwater during different seasons as well as stages in their life cycle. The species was abundant during the 19th century, however, the population decreased during the early 1900s with the last known sighting of the fish in 1923. 
In 1951, some years after the last sighting, the species was given full legal protection by the Freshwater Fisheries Regulations, the only New Zealand native freshwater fish to be protected.
In August 2018 the New Zealand Department of Conservation classified the New Zealand grayling as "Extinct" under the New Zealand Threat Classification System.
Description.
The New Zealand Grayling matured between 30-45cm in length and slender in shape with the presence of an adipose fin. As an amphidromous fish, when migrating between freshwater and saltwater during, it was found that graylings, originally silver in colour, would darken to a grey or brown, and turn occasionally gold, while the underbelly remained light.
Distribution.
The New Zealand grayling was widely distributed throughout both the North and South islands of New Zealand throughout the 1800s, however, the distribution of the fish decreased to more isolated parts of New Zealand throughout the 20th century. The fish was found in freshwater rivers and streams during Autumn and Winter, however, migrated to New Zealand’s surrounding seas early in Spring. The fish was believed to spawn in freshwater rivers before migrating to the sea and returning to freshwater to reproduce.
Angling and Hunting.
The New Zealand grayling were often hunted by the natives of New Zealand. A traditional way the Māori people hunted the New Zealand grayling was by using a basket trap known as a “hīnaki”, lodged in a river to capture fish swimming downstream. The traps were often left overnight so by morning, fish that were guided into the trap by the mānuka brush walls would be caught at the top of the tapered “V”, not being able to swim back against the current to avoid being caught. Another method used by the Māori people incorporated people chasing the fish with spears or weapons to lead them into the “V” shaped traps. 
Threats and Extinction.
There has been no confirmed primary cause for the extinction of the New Zealand grayling. However, multiple sources note that there was not a single cause for the extinction, but multiple subtle factors, which when combined, led to the abrupt disappearance of the fish which was once in abundance.
Being an amphidromous species and spending part of its life in freshwater rivers and streams, the New Zealand grayling were at risk of population decline and extinction due to the fragility of freshwater systems. Deforestation has been identified as a process that threatens freshwater systems as runoff can lead to habitat degradation, causing erosion and increased river sediment. Another threat to freshwater systems is pollution, where pollution of waterways, at the hand of man, pose a great threat to existing organisms which inhabit those areas. 
One of the factors believed to have contributed to the extinction of the New Zealand grayling include the theory of source-sink dynamics. Rivers and streams which supply an optimal habitat for ecosystems are known as sources, whereas those which do not provide the same level of environmental characteristics due to pollution, overfishing or introduced species, are known as sinks. As the presence of sink rivers increased through pollution, caused by industrial development, introduced species from European settlers and overfishing, the availability of source rivers decreased accordingly. When at sea the New Zealand grayling faced little to no threat, but when migrating back to freshwater rivers or streams faced the threat of entering a sink river, where breeding and inhabiting conditions are unfavourable. As the New Zealand grayling were known to migrate in large shoals, if migration to a sink river occurred, a significant proportion of the population would either find it difficult to reproduce, decreasing the amount of offspring in the next generation, or die off. The increase in sink rivers therefore posed a significant threat to the amphidromous species, as the availability of source habitats decreased and turned to habitats with less than favourable conditions. 
Another factor assessed to be a cause for the extinction of the species is the harvesting of the fish. Along with the Māori people hunting the New Zealand grayling, the settlement of the Europeans resulted in an increase of fishing. The increase in hunting for the fish, as it was in abundance, led to a decline in the population and eventually extinction, as the reproductive capacity of the fish was inundated.
The final factor believed to have triggered the rapid decline and subsequent extinction of the population of the New Zealand grayling is the aftermath of introduced trout species from European settlement. Brown trout were introduced into the southern oceanic regions during the 1860’s and to New Zealand by 1920. The introduction of brown trout affected endemic species, such as the New Zealand grayling, as it created more competition for food and resources. 