Honson Pit Viper – Trimeresurus honsonensis – (Grismer, Ngo & Grismer, 2008)

Science name: Trimeresurus honsonensis – (Grismer, Ngo & Grismer, 2008)

Taxonomic:  Animalia>> Chordata>> Reptilia>> Squamata >> Viperidae >> honsonensis

Species status: Endemic ; IUCN status: LC (Least Concern)

Description:

Physical Characteristics:

Size: Females can grow to a maximum snout-vent length (SVL) of 557 mm, with males measuring up to 523 mm. The tail length (TaL) to SVL ratio is 0.15–0.16 for females and 0.23 for the single recorded male.
Scales: 21 dorsal scale rows at midbody, 183-186 ventral scales in females and 186 in males, and 54-58 subcaudal scales in females and 74 in males. The occipital and temporal scales are smooth.
Distinct Features: The species lacks a ventrolateral stripe and a red or reddish-brown tail, which are common in related species. Instead, it exhibits a dull-yellow to brown ground color.
Coloration and Appearance:
The body has dark bands against a dull-yellow to brown background, giving the species a muted appearance. Unlike other Trimeresurus species, this viper does not display the typical vibrant green coloring or red tail, which further distinguishes it from other pit vipers in its genus.

Distribution and habitat:

Elevation:
The Hon Son Pit Viper (Trimeresurus honsonensis) is found at elevations ranging from 0 to 450 meters above sea level on Hon Son Island, located in the Kien Hai District, Kien Giang Province, southern Vietnam.

Area:
This species is endemic to Hon Son Island, which covers approximately 22 km². The island is composed primarily of large granitic boulders, stretching from the shoreline to its peaks. There is minimal primary vegetation remaining due to habitat alteration, making the natural environment mainly rocky and coastal. Trimeresurus honsonensis has not been observed on other nearby islands despite multiple surveys.

Habitat:
The Hon Son Pit Viper inhabits rocky outcrops and coastal cliffs surrounded by bamboo vegetation. The snakes are commonly found resting on rocks or within bamboo growth, typically emerging in the afternoon or evening after rainfall. Its natural habitat is classified as marine coastal/supratidal, with the snake living close to sea cliffs and rocky offshore environments. The lack of primary vegetation suggests that it is adaptable to more barren, rocky environments.

Behaviour and ecology:

Lifestyle:
This species is likely nocturnal and can be found in the late afternoon or evening, often after rainfall. Trimeresurus honsonensis is ovoviviparous, meaning the eggs develop inside the female, and live young are born. It is a predator, feeding mainly on small vertebrates such as geckos.

Reproduction:
While specific reproductive data are lacking, Trimeresurus honsonensis is presumed to follow an ovoviviparous reproductive strategy, like other members of the genus. This means the young are carried internally and born live rather than hatching from external eggs.

Conservation and status:

IUCN Red List Category and Criteria:
The Hon Son Pit Viper is listed as Vulnerable under criterion D2 on the IUCN Red List due to its restricted range and specific habitat requirements. The most recent assessment occurred in 2011, and the species continues to face threats from habitat degradation on the small island it inhabits.

Population Trend:
The population is considered stable, although there is limited information available on the exact number of mature individuals. The species is confined to a small geographic area, which makes it vulnerable to environmental changes and human activities.

Threats:
The primary threat to Trimeresurus honsonensis is habitat degradation on Hon Son Island. The island has seen a reduction in primary vegetation, which could impact the species’ long-term survival, although it appears to tolerate altered habitats to some extent. Additionally, its limited range increases its susceptibility to environmental pressures.

Conservation Actions:
There are no specific conservation actions in place for Trimeresurus honsonensis. However, the species’ vulnerability due to its limited range calls for habitat protection on Hon Son Island. Further research is needed to assess its population dynamics and ecological requirements, which could inform conservation strategies.

Etymology
The species name “honsonensis” refers to the type locality, Hon Son Island, where the snake was first discovered. This honors the importance of the region and highlights the species’ geographic specificity.