12 | MAY 2016
Where Have the Largest
Whale Sharks Gone?
Marine biologists have raised concerns about the whereabouts
of the world’s biggest whale sharks after inding that the largest
sharks observed in recent years were smaller than those recorded
more than a decade ago.
Dr Ana Sequeira of The University of Western Australia’s
Oceans Institute, who led the study, said it was important to
know the size of whale sharks because it provided information
about their population status. However, it’s diicult to obtain
accurate size estimates as this needs to be done while they are
freely swimming.“A common technique is to compare the sharks with
an object of known size while swimming alongside
them. However, these estimates are often inaccurate,”
Sequeira said. “We found the margin for error increased
as the actual size of the target increased, which meant
that big sharks of around 10–11 metres were mistak-
enly thought to be up to about 3 metres smaller.”
The new study, published in Royal Society Open
Science(http://tinyurl.com/jle7hpm), “compared visual
estimates of whale shark sizes with those obtained using
an underwater stereo-video system”. This found that the
largest sharks observed at Ningaloo Reef in recent years
were smaller than those recorded at the same location
more than a decade ago. “The majority of whale sharks
seen at Ningaloo were juveniles with mean lengths of
around 6 metres which, given the fact that the ish reach
maturity when they are about 9 metres long, prompts
the question: where are the adults?”
Study co-author Dr Mark Meekan of the Australian Institute
of Marine Science said that, apart from groups of large females
reported at two locations in the eastern Paciic Ocean, there was
a lack of adult whale shark sightings around the world. “Co-occur-
rence of adult males and females ensures the survival of a species,
so not knowing the whereabouts of adult whale sharks and how
many still exist presents a challenge for understanding their conser-
vation status,” he said.
Meekan said that more research is needed to help locate large
whale sharks and to clarify the number of mature animals still in
existence. “Understanding the whereabouts of the biggest whale
sharks will also help us understand how human activity such as
industrial developments, isheries and boat strike might impact
the animals,” he said.Gravitational Waves Can Be
Found Closer to Home
While gravitational waves were detected a billion light years away
earlier this year, they may soon be identiied throughout “the
observable universe”.
Prof David Blair of the Australian International Gravitational
Research Centre at The University of Western Australia said that
“cat-lap” pendulums less than 1 mm in size could be retroitted
to existing gravitational wave detectors, enabling physicists to
record hundreds of gravity wave events every day.
“Currently the detectors can only detect huge tsunami-like
waves, but with the new technology we would be able to extend
that range about seven times,” Blair said. “One of our PhD students,
Jiayi Qin, has tested the concept as part of her thesis with very
good results, and we will now look to test the technology further.”
Blair is part of an international team that has spent the past
7 years putting together detector equipment that uses powerful
lasers to measure vibrations of mirrors suspended 4 km apart at
the ends of huge vacuum pipes.
The gravitational waves announced earlier this year were produced
during the inal fraction of a second of the merger of two black holes
to produce a single, more massive spinning black hole. This collisionof two black holes had been predicted but never observed.
However, the detectors have industrial applications too. “Grav-
itational wave technology is already being applied to mineral explo-
ration, time standards, quantum computing, precision sensors,
ultra-sensitive radars and pollution monitors,” Blair explained.Jiayi Qin and Prof David Blair test the new technology.