New Zealand grayling

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New Zealand grayling
Southern Pacific fishes illustrations by F.E. Clarke 100 1.jpg

Extinct  (1927) (IUCN 3.1)[1]

Extinct  (1927) (NZ TCS)[2]
Scientific classification edit
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Osmeriformes
Family: Retropinnidae
Genus: Prototroctes
Species:
†P. oxyrhynchus
Binomial name
†Prototroctes oxyrhynchus
Günther, 1870

The New Zealand grayling (Prototroctes oxyrhynchus) 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.[3] The variety of names for the fish came from either other tribes or to describe the fish at different periods of its life cycle.[3] 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, however, is closely related to the Australian grayling (Prototroctes maraena).[3][4] The New Zealand grayling was an amphidromous species, migrating between freshwater and saltwater during different seasons as well as stages in their life cycle.[5] 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.[6]

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.[7]

In August 2018 the New Zealand Department of Conservation classified the New Zealand grayling as "Extinct" under the New Zealand Threat Classification System.[2]

Taxonomy[]

The New Zealand grayling, previously part of the family Prototroctidae, is part of the family Retropinnidae which contains smelts and graylings found in the southern hemisphere.[4] Previously, smelts and southern graylings were classed into two separate families, Prototroctidae for graylings and Retropinnidae for southern smelts, however, now all six species under these families are classed as Retropinnidae.[4][8] The fish is part of the Genus Prototroctes, which contain two species, the New Zealand grayling (Protroctes oxyrhynchus) and the Australian grayling (Prototroctes maraena).[9]  

Description[]

The New Zealand Grayling was a medium sized fish which 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.[5]

Dentition[]

The dentition of the fish comprises a blunt and rounded snout, with the upper jaw containing a single row of long, blunt teeth which are situated close together forming a “comb like” structure. The lower jaw which contains another single row of smaller and sharper teeth is slightly shorter than the upper jaw, and is less rounded, forming a point which fits just inside the row of teeth on the upper jaw. [10]

Diet[]

The dentition and digestive system of the New Zealand grayling suggests the fish was omnivorous, feeding on both aquatic larvae such as caddisflies[11] and plants such as waterweeds growing on the rocks on riverbeds.[12] The New Zealand grayling is suspected to have been herbivorous at times.[10][12]

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 such as some streams in the East Cape, Wairarapa and Otaki districts on the North Island and on the west coast of the South Island.[3] The fish was found in freshwater rivers and streams during Autumn and Winter, however, migrated to New Zealand’s surrounding seas early in Spring.[5] The fish was believed to spawn in freshwater rivers before migrating to the sea and returning to freshwater to reproduce.[13]

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.[3][14] 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. This method of catching the fish was effective as it allowed dozens of fish to be captured at a single time. Another method used by the Māori people incorporated people chasing the fish with spears or weapons to lead them into the “V” shaped traps.[3]

Threats and Extinction[]

The cause for the extinction of the New Zealand grayling is only speculation as the fish went extinct around the 1920s, and as such, 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.[3][15][13]

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.[16]

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.[13] 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 unfavorable. 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 favorable 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.[15]

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 including New Zealand in 1867; rainbow trout were introduced in 1883.[17][18]

The introduction of both brown and rainbow trout affected endemic species, such as the New Zealand grayling, through direct predation and competition for food and habitat. The non-native oomycete pathogen vectored by introduced trout may also have played a strong role in the extinction of New Zealand grayling, particular in waters that, with the exception of trout introduction, appeared remote and undisturbed. is inevitably introduced with salmonids and is strongly implicated in very severe fish kills of the closely related Australian grayling soon after trout introduction in Australia.[19]

References[]

  1. ^ West, D.; David, B.; Ling, N. (2014). "Prototroctes oxyrhynchus". IUCN Red List of Threatened Species. 2014: e.T18384A20887241. doi:10.2305/IUCN.UK.2014-3.RLTS.T18384A20887241.en. Retrieved 20 November 2021.
  2. ^ a b Dunn, Nicholas R.; Allibone, Richard M.; Closs, Gerard P.; Crow, Shannan K.; David, Bruno O.; Goodman, Jane M.; Griffiths, Marc; Jack, Daniel C.; Ling, Nicholas. Jonathan M. Waters and Jeremy R. Rolfe. "Conservation status of New Zealand freshwater fishes, 2017" (PDF). New Zealand Threat Classification Series. Department of Conservation. 24: 8.
  3. ^ a b c d e f g Allen, K. Radway (1949). "The New Zealand Grayling - A Vanishing Species". Tuatara. 2: 22–26.
  4. ^ a b c "RETROPINNIDAE". fishesofaustralia.net.au. Retrieved 2021-05-31.
  5. ^ a b c McLintock, Alexander Hare; Lawrence James Paul, B. SC; Taonga, New Zealand Ministry for Culture and Heritage Te Manatu. "GRAYLING". An encyclopaedia of New Zealand, edited by A. H. McLintock, 1966. Retrieved 2021-05-03.
  6. ^ Holdaway, Richard (2007). "Extinctions - Smaller birds, reptiles, frogs, fish, plants". Te Ara - the Encyclopedia of New Zealand.
  7. ^ Mitchell, Charlie (14 February 2018). "The enduring mystery of our only protected freshwater native fish". Stuff. Retrieved 24 September 2018.
  8. ^ "ADW: Prototroctes: CLASSIFICATION". animaldiversity.org. Retrieved 2021-05-31.
  9. ^ McDowall, R. M. (1976). "Fishes of the family Prototroctidae (Salmoniformes)". Marine and Freshwater Research. 27 (4): 641–659. doi:10.1071/mf9760641. ISSN 1448-6059.
  10. ^ a b McDowall, R. M. (1974). "Specialization in the dentition of the southern graylings—genus Prototroctes (Galaxioidei: Prototroctidae)". Journal of Fish Biology. 6 (2): 209–213. doi:10.1111/j.1095-8649.1974.tb04538.x. ISSN 1095-8649.
  11. ^ 1887-1965., Graham, David H. (David Henry) (1974). A treasury of New Zealand fishes. A.H. & A.W. Reed. ISBN 0-589-00891-9. OCLC 56915631.CS1 maint: numeric names: authors list (link)
  12. ^ a b Elsdon., Best (1986). Fishing methods and devices of the Maori. Ward Government Printer. OCLC 311993220.
  13. ^ a b c Lee, Finnbar; Perry, George L. W. (2019). "Assessing the role of off-take and source–sink dynamics in the extinction of the amphidromous New Zealand grayling (Prototroctes oxyrhynchus)". Freshwater Biology. 64 (10): 1747–1754. doi:10.1111/fwb.13366. ISSN 1365-2427.
  14. ^ McDonald, James Ingram; Taonga, New Zealand Ministry for Culture and Heritage Te Manatu. "The last grayling". teara.govt.nz. Retrieved 2021-05-17.
  15. ^ a b Allibone, R.; David, B.; Hitchmough, R.; Jellyman, D.; Ling, N.; Ravenscroft, P.; Waters, J. (2010-12-01). "Conservation status of New Zealand freshwater fish, 2009". New Zealand Journal of Marine and Freshwater Research. 44 (4): 271–287. doi:10.1080/00288330.2010.514346. ISSN 0028-8330.
  16. ^ Dudgeon, David; Arthington, Angela H.; Gessner, Mark O.; Kawabata, Zen-Ichiro; Knowler, Duncan J.; Lévêque, Christian; Naiman, Robert J.; Prieur‐Richard, Anne-Hélène; Soto, Doris; Stiassny, Melanie L. J.; Sullivan, Caroline A. (2006). "Freshwater biodiversity: importance, threats, status and conservation challenges". Biological Reviews. 81 (2): 163–182. doi:10.1017/S1464793105006950. ISSN 1469-185X. PMID 16336747.
  17. ^ Butcher, A. D. (1967). "A changing aquatic fauna in a changing environment". Proceedings and papers of IUCN 10th technical meeting, Lucerne, June 1966; Part III – Changes due to introduced species; section 2 – Ecological effect of introduced animal species.
  18. ^ Flecker, Alexander S.; Townsend, Colin R. (1994). "Community-Wide Consequences of Trout Introduction in New Zealand Streams". Ecological Applications. 4 (4): 798–807. doi:10.2307/1942009. ISSN 1939-5582. JSTOR 1942009.
  19. ^ Kaminskas, S. (2020). "Alien pathogens and parasites impacting native freshwater fish of southern Australia: a scientific and historical review". Australian Zoologist. doi:10.7882/AZ.2020.039.
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