Report on the finding of introduced species, Saproscincus rosei (Rose’s shadeskink), on the Swan Coastal Plain Western Australia

M.A. Cowan, B. Shepherd, P. Doughty and M. Bamford – January 2020

On the 24th and 27th of May 2019 an ecologist from Bamford Consulting (Dr Barry Shepherd) caught six individuals, and sighted another, of a species of skink from the genus Saproscincus, a group of around 11 species of small skinks found along parts of the eastern seaboard of Australia. While DPIRD and DBCA were notified of this finding and attempts made to identify it to species, no formal determination of the species was made, and no specimens were lodged with the WA Museum (WAM).

In December 2019 the Curator of Herpetology at the WA Museum, Dr Paul Doughty was informally notified of the discovery. Discussions between Dr Doughty, Dr Mike Bamford, Dr Barry Shepherd and Mr Mark Cowan (DBCA Senior Research Scientist) resulted in a decision to attempt to capture several specimens for formal identification and lodgement within the collections of the WAM, as well as to more formally document the presence of the species at a location in Western Australia.

On 19 January 2020, ten funnel traps were set for a single night in an area towards the north eastern corner of Lake Joondalup (31°43'20"S and 115°46'59"E) where Bamford Consulting had previously found the skink. Each funnel was set in the middle of a short drift fence (~4m) and these were established in a transect running from peripheral vegetation towards the lakes edge over a distance of around 100m. During the setting of the traps a juvenile Saproscincus sp. was caught by hand and when traps were checked the following day a further four adults (one gravid female and three males) were caught in traps, while another juvenile was also caught by hand. The two juveniles and three of the adults (one female and two males) were lodged with the WA Museum and the other adult male has been retained by DBCA. Museum numbers for the lodged specimens are R165496-7 for the juveniles, R165498 and R165500 for the two males and R165499 for the female.

The specimen retained by DBCA has a field number of MAC2366 and tissue was also taken from this specimen (same field number). Figure 1., below, shows the general area where the reptiles are thought to occur (white outline), the location of a sighting of a specimen by Dr Shepherd in May 2019 ( white square with black centre) and, the locations where traps were set and specimens were caught in May 2019 and in January 2020 (white circles with black centres).

From these most recent captures the species has now been formally identified by Dr Doughty as Saproscincus rosei, commonly known as Rose’s shadeskink. The species is endemic to the near coastal margins of northern New South Wales and southern Queensland (Figure 2.) where it is predominantly associated with moist shaded forest habitats (Cogger 2014).

The fact that two juvenile animals were caught along with a gravid female shows the species is successfully breeding adjacent to Joondalup Lake. For the majority of local reptile species reproductive activity occurs through spring with egg deposition for oviparous species in late spring or early summer (Davidge 1980). The simultaneous occurrence of juvenile hatchlings and a gravid female of S. rosei in late January indicates an extended breeding period for this species with polyoestrous ( multiple clutches of eggs) a possibility. The number caught with a very small trapping effort also indicates that it is relatively abundant in this vicinity. The full extent of occurrence around Lake Joondalup is unknown but as the well vegetated margins of the lake appear to provide suitable habitat, it may well have a larger distribution then where it has currently been found.

Figure 1. Location of traps (circles), sighting (square) and boundary (shaded area) at Lake Joondalup.

Figure 2. Distribution of Saproscincus rosei (Cogger 2014). The following brief description is taken from Cogger (2014) and a picture of an adult male is shown in Figure 3. Colouration is greyish-brown to reddish-brown above, occasionally with numerous pale and dark scales forming a variegated pattern. A dark streak is present along the upper lateral edge of the snout and continues behind the eye and above the ear, and then as a broad dark upper lateral zone, usually broken by pale blotches. There is a pale spot on the back and at the base of the hindlimbs. Ventral surface is pale cream or yellow, with yellow usually in front of the vent and along the base of the tail. Individuals reach around 60mm snout-vent length and the tail may be as much as 160% of the SVL. Frontoparietal scales are paired, eyelid is moveable with a small transparent disk and subdigital lamellae are smooth.

Figure 3. Adult male Saproscincus rosei from lake Joondalup.

Superficially and without proper examination this species could possibly be confused with several locally occurring skinks of similar size including Acritoscincus trilineatus, Morethia obscura and Cryptoblepharus buchananii. However key aspects for differentiating S. rosei from these include the presence of paired frontoparietals (Figure 4) as these scales are either fused with the interparietal to form a large quadrilateral shield (C. buchananii and M. obscura) or they are fused together to form a single frontoparietal scale with only a small interparietal scale (A. trilineatus). Only S. rosei and A. trilineatus possess a moveable eyelid (Figure 5) – the other two species have an immoveable transparent disk. The presence of the pale spot at the back of the thigh (Figures 3 and 7) also differentiates S. rosei from the three others. S. rosei usually have only six upper labial scales (Figures 5 and 6) whereas the other three species usually have seven. Other characteristics include the absence of ear lobules (scales lining the ear opening and projecting inwards -Figure 5) and subdigital lamellae (scales under the fingers and toes) are smooth and rounded (Figure 8).

Figure 4. Photograph showing the distinctive paired frontoparietal scales.

Figure 5. no ear lobules present and lower eyelid moveable. Figure 6. usually six upper labial scales present.

Figure 7. conspicuous pale spot at the back and base of thigh. Figure 8. subdigital lamellae smooth.

It is unknown what threat, if any, a species such as this poses to other biodiversity values and given its preference for damp shaded environments it may not survive well outside the confines of the lake’s riparian vegetation. The source of the population is not known, and neither is the distributional extent in the immediate vicinity. As already noted, it appears to be surviving well with reproduction occurring and it may constitute a competitive threat to other ground dwelling species, including some of those noted above.

In the immediate future it may be worthwhile to at least determine and document the extent of occurrence around Lake Joondalup and it may also be worthwhile considering what quarantine measures could be put in place to restrict movement of material and inadvertently S. rosei to other locations. It is not obvious as to what measures could be taken to eradicate the species so some form of monitoring and perhaps containment may be the only options available at this stage.

References

Cogger, H. (2014) Reptiles and Amphibians of Australia. CSIRO Publishing, Collingwood

Davidge, C. (1980) Reproduction in the Herpetofaunal Community of a Banksia Woodland near Perth, W.A. Australian Journal of Zoology, 28:3, p.435 – 443

Wilson, S. and Swan, G. (2013) A Complete Guide to Reptiles of Australia, Fourth Edition. New Holland Publishing, London.