April 22, 2014 | 2
The Mercury Islands tusked weta (Motuweta isolata) isn’t exactly a thing of beauty. These massive New Zealand insects can reach more than seven centimeters in length, including the impressive tusks in front of their jaws that they use to push their prey around. But size and bullying strength didn’t necessarily help this weta, one of about 70 similar species. Although it may have once lived on the New Zealand mainland and several islands in the Mercury island group, researchers believe that invasive rats may have wiped the Mercury Islands tusked weta in all but one location. By the mid-1990s it could only be found on the 13-hectare Middle Island, where the population was estimated at fewer than 200 individuals.
That’s when the New Zealand Department of Conservation—which feared that rats could arrive on Middle Island and wipe out the few remaining wetas—set out to save the species. The process began in 1993 when two females and one male were captured on Middle Island. Captive-breeding efforts began in 1994. As detailed in a 2005 paper in Conservation Evidence, this first group of breeders produced 15 healthy offspring. Two of the females from that batch were mated with another male captured from Middle Island in 1998, which produced more than 500 eggs. Although many of those eggs died, 181 captive-born juveniles were transferred to three different facilities for research and additional breeding.
Researchers quickly realized that they needed to rear the juvenile insects individually due to their carnivorous (and potentially cannibalistic) nature. They were raised to about half their eventual size in captivity, at which point they were large enough to defend themselves from spiders, beetles and other invertebrate predators. After that, beginning in the year 2000, releases of the captive-bred insects began on Double and Red Mercury Islands, which had been cleared of invasive mammals in anticipation of their reintroduction. Additional releases followed in 2002 and 2003.
Surveys in the following years found eggs and new juveniles, indications that the insects were breeding in their new homes. The wetas did so well, in fact, that 75 of them were transferred from Double Island to Cuvier Island in 2008, according to a paper published April 13 in the Journal of Insect Conservation. (They do not yet appear to be breeding on their own on Cuvier.) Additional captive-bred wetas were released on three other islands, although they have to date stayed within 100 meters of their release sites and not spread across the islands as they have in other locations.
All of this, it turns out, happened just in time. Eight surveys conducted on Middle Island between 2009 and 2012 failed to turn up any evidence of the insects. The authors of the new paper suggest that the weta may no longer be found on the one island that was previously its home. In fact, none have been seen there since 2001. No one knows why, exactly, they vanished.
In their new paper the authors admit that efforts on Middle Island might have failed but they consider the overall translocation program “a significant conservation success.” In other words, the species probably would have gone extinct without this work. That’s cause for celebration.
Photo by Graeme Churchard via Flickr. Used under Creative Commons license