some tiger sharks travel thousands
of kilometres, and the fact that at its
widest, TRNP stretches around 50
kilometres, it would not be a surprise
if sharks moved beyond the boundaries
of the park. Still, a rich environment
like TRNP may decrease the desire to
roam, depending on how the sharks
are using the area.
To find out more, LAMAVE and TMO
took two approaches: First, the team
deployed satellite tags to find out
where the sharks were going; they also
used acoustic tags to understand how
they were using the park.
TAGGING TIGERS
In May 2016, TMO and LAMAVE
researchers successfully tagged the
first tiger shark in the Coral Triangle:
A 3.4-metre female was fitted with
an ARGOS-transmitting dorsal fin-
mounted satellite tag. The team tagged
a second tiger shark in 2017. These
tags have a small antenna and a wet/
dry switch that is triggered when it
breaks the surface.The tag interacts
with passing ARGOS-system satellites,
and when both the tag and satellite
align, location and temperature data is
transmitted. A successful transmission
results in an email disclosing the
location of the shark and whether
the individual is inside or outside the
boundary of the park.
However, the technology is not
without its challenges and the shark’s
position is only reported when the tag
breaks the surface, a limitation when
working with sharks, as unlike marine
mammals, they do not need to break
the surface. As a result, transmissions
can be few and far between, offering
only few, or no clear conclusions.
However, the limitations of one
technology can be counteracted
by another – a different approach,
different tagging, different questions.
Acoustic tags work very differently to
satellite tags. Rather than transmitting
to a satellite, they transmit to acoustic
receivers. These canisters are about
a foot long, weighted down and placed
around the area of interest. In this
case, the team positioned them in
various locations on the south and
north atolls, and one at Jessie Beazley
Reef. At the same time, the team
set out to deploy the tags. Using bait
on modified barbless hooks, they
momentarily occupied the shark long
enough to turn the shark upside down
into tonic immobility, a trance-like
state, which allowed the acoustic tag to
be fitted. Throughout the process, vital
signs were monitored and as soon as it
was safe, the shark was released and
swam off across the reef.
Once tagged, sharks swimming
within 500 metres of a receiver
transmit a unique signal which is then
recorded. Located around 30 metres
deep, the receivers are regularly
collected and the data downloaded;
once cleaned, they can be redeployed.
As more signals are collected, they
create a movement map highlighting
where and how frequently the sharks
use specific areas of the park.
To date, 20 animals encountered in
the park have been fitted with acoustic
tags: two tiger sharks, 14 grey reefsharks, and four reef manta rays.
The research is ongoing and many
of the tags will last up to 10 years.
New acoustic receivers are being
placed in the park, which will help
build a more detailed map of the
animals’ movements. The team will
also expand the acoustic network
in 2018 deploying receivers in the
waters of Cagayancillo, an archipelagic
municipality located around 130
kilometres northeast of TRNP.
While acoustic data collection is
ongoing, preliminary results from
the satellite tags have shown that at
least one of the tagged tiger sharks
has ventured beyond the boundaries
of TRNP – a worrying prospect, as
tiger sharks do not enjoy general
protections in Philippine waters.
On August 8, 2017, the Philippine
Navy seized 10 Vietnamese nationals
aboard a fishing vessel intercepted
in northwest Palawan; they were
carrying around 70 sharks, including
tiger sharks. Two days later, poaching
charges were filed against them. While
the fishing vessel was intercepted
approximately 350 kilometres north
of TRNP and had not entered the park,
it is clear that sharks outside TRNP
are in danger from illegal and
unreported fisheries.
UNESCO World Heritage Sites
like TRNP are considered to have
outstanding universal value and
are important to all of humanity
across generations. In a world where
oceans are reaching breaking point,
protected areas, when properly
managed and enforced, are a lifeline
for near-threatened species like tiger
sharks. Learning what we can about
tiger sharks and their range will be
essential to ensure their future within
the Philippines. ADLarge Marine Vertebrates
Research Institute Philippines
(LAMAVE) is the largest
independent non-profit non-
governmental organisation
dedicated to the conservation
of marine megafauna and their
habitats in the Philippines.
LAMAVE strives for
conservation through scientific
research, policy and education.
You can follow the work of
LAMAVE and TMO at
http://www.lamave.org and
http://www.tubbatahareefs.orgLEFT: LAMAVE researcher Gonzalo Araujo
makes final adjustments to an acoustic
receiver positioned on the slope of the
south atoll. The receiver will pick up
signals from tagged sharks that swim
within a 500-metre range
IMAGE: Noel Guevara (LAMAVE)Supported by