IS there a baby killer on the loose in Hyde Park?
A UWA study has revealed that the oblong turtle population at the park is large and healthy, but old, with very few juveniles found in the last 15 to 20 years.
“Once they reach the limit of their natural life, the population may suddenly collapse,” Vincent council staff reported.
City of Vincent commissioned the study after concerns grew about a lack of turtle babies at the lakes in recent years, leaving them looking like a turtle retirement home.
The oblong turtle species is classified as “near-threatened” and urban populations are under threat across the city.
Across 2015/16 a total of 114 mature turtles were captured, tagged and released back into the Hyde Park lakes, but not a single hatchling or juvenile was caught, and not many were found at lakes in Claremont, Jualbup and Booragoon either.
The $5000 UWA study by Blaine Hodgson and Roberta Bencini suggested a few reasons for the lack of young turtles: either they’re being eaten as eggs in the nest, or as hatchlings, or the grown ups are not reproducing.
The turtles should be breeding, as ultrasound scans of the captured females showed many of them were egg-bearing.
It’s also not a sex imbalance issue: at some urban lakes there are many more male turtles than females (because females sometimes venture out of the lake and cross roads to make new nests and get run over).
At Hyde Park they only go back and forth between the two lakes, so there’s a pretty even mix with only slightly more lady turtles.
The 2013 Hyde Parks lake restoration project has slightly improved the turtle’s prospects, with soft beaches at parts of the lake that turtles can shuffle out of, where there used to be steep walls.
The water’s also cleaner with filters stopping road run off, and more vegetation (especially on the eastern island) should make it easier to nest.
But four years on, the bubbies are still missing.
The researchers also captured a southern shortfin eel, a carnivorous predator that could eat hatchlings, probably an ex-pet released into the lake.
Another one was taken out four years ago, and in previous years there were sightings of an exotic red-eared slider turtle that competes with the native oblongs.
The report recommends further study to work out what’s going on, possibly involving setting up fake nests to see if foxes are eating babies.
Vincent councillors will vote on whether to spend about $28,000 to extend the study for another four years at Tuesday night’s council meeting.
by DAVID BELL