Metal Detectors Aid Aquaculture Researchers
Trying
to study shellfish populations has long been a difficult task
for marine biologists. Finding
a way to locate and track individuals and groups of animals has
proven quite a challenge for researchers.
Dr. Tasman Crowe, a scientist with the Australian Centre
for International Agriculture, has experienced these
difficulties first hand. Dr.
Crowe is involved in a stock enhancement project of trochus, a
conical shaped marine gastropod (snail) that inhabits shallow
tropical reefs. The
shell of an mature adult can measure up to 5 inches. Smaller
shells are used to make jewelry and buttons for high priced
garments. The
current global demand for trochus shell is over 7,000 tons
annually. Like many of today’s marine resources, the trochus fishery
is under stress from over fishing and scientists are
investigating the feasibility of a trochus reseeding project.
Dr. Crowe wrote a paper on the subject for the Secretariat of
the Pacific Community. In
the report he discusses the difficulty of tracking and capturing
tagged animals in a complex habitat.
“The trochus often move into and under the live coral
or coral ruble and can not be found by visual searches.
In order to conduct an accurate census, field researchers
need a way to locate animals hidden by coral and disguised by
debris in a marine environment of varied terrain.”
Dr.
Crowe came up with the novel idea of connecting a very small
metal tag to the trochus shell.
He wrote, “To solve the problem we used underwater
metal detectors to locate small metal tags fixed to the animals.
The metal detector we used was a Pulse 8X supplied by JW
Fishers Mfg.” He went on to extol the virtues of the detector
for the this type of project and adds, “We found the smallest
tag that could fit on the juvenile trochus and still be reliably
detected was a 0.3 gram piece of aluminum. Tags were detectable within a range of 8 cm of the coil
regardless of the intervening medium (e.g. air, water, rock,
sand, or coral) and could be pinpointed to within 1 to 2 cm.
The report concluded with, “The effectiveness of the
system was tested in a series of pilot trials and the results
indicated the tagging system was an effective method of finding
trochus. Over 85% of a known number of juveniles were
consistently recaptured.”
Another
group using underwater metal detectors in a similar project are
scientists at Canada’s Dept. of Fisheries and Oceans at the
Maurice Lamontagne Insitute in Quebec.
“I am using Fishers Pulse 8X to locate marked clams on
the seashore at low tide”, says marine biologist Francois
Hazel. “The
detector works very well in helping us locate clams affixed with
small metal tags. We
can gather information on growth rates, migration patterns, and
other characteristics of the population.
This is an exploratory project to develop tools that will
one day assist communities in monitoring their coastal zones.
My hope is that in the future this equipment can be used
by other groups, such as schools, in a type of
“treasure hunt” to increase awareness about coastal
species - mixed with some fun.”
