Marine Turtle Acoustic Deterrent System

VCU

Turtle shell and ear are acoustic detectors

Marine Turtle Hearing

unconditioned behavioral responses

  • Convert vibration acceleration thresholds to displacement

displacement = 0.248 X acceleration / Hz2

 

  • Convert displacement to SPL in water equivalent

SPLe = displacement + k +62 dBa

k = ~60 dB

a = water reference + impedance of sound in water

marine turtle acoustic deterrents

Three classes of audio:
  1. < 200 Hz
  2. 200 - 900 Hz
  3. 900 - 15,000 Hz

 

Three forms of delivery:

  1. standard acoustic (can be pulsed or modulated)
  2. AM on low frequency ultrasound
  3. AM on MHz ultrasound
  • low frequency < 200 Hz
  • sensitive hearing frequencies (200 - 900 Hz)
  • middle ear resonant frequencies (.9 - 15 kHz)
  • any of the above (1 - 3) amplitude modulated with low frequency ultrasound (15 - 100 kHz)
  • any of the above (1 - 3) amplitude modulated with MHz frequencies (0.1 MHz +)
Turtle deterrent system

Phase 1: Basic System

 

Borneo field study

in progress

Excluding turtles from the seaweed culture site with sound
Testing in progress.

Dynamic range of marine turtle hearing

Threshold to temporary threshold shift in noise

(dynamic range is about 70 dB)

 

Ear Model

 

Aquatic turtle middle ear resonance

modeled as a cylinder after Weaver and Vernon, 1956

 

Ultrasonic aquatic turtle middle ear resonance

modeled as a cylinder after Weaver and Vernon, 1956

Dec 09, 2001

World Focus: Sea Turtles Under Seige

Slowly fading away Human activity endangers species

BY PAULINE JASUDASON
THE ASSOCIATED PRESS

MA'A DAERAH, Malaysia Elegant and virtually weightless in the water, a rare green sea turtle swaps agility for awkwardness and drags herself out of the surf on a biennial pilgrimage of procreation.

Under cover of darkness and lugging a 220-pound, heart-shaped shell, the turtle struggles beyond the high-tide mark and starts digging a nest for her more than 100 eggs. Huge flapping flippers send sand flying in all directions.

Eggs laid, the exhausted turtle shovels sand into the hole to cover them, then makes the arduous trek back to the water.

Watching the tortuous process from nearby, Wan Rozaimy Wan Ramli barely waits until the turtle has gone before stepping up to the nest, scooping away the sand and plucking out the eggs one by one.

Sea turtles have existed virtually unchanged for more than 100 million years. But human activity, including taking eggs - considered an aphrodisiac in some parts of Asia - has pushed several species to the brink of extinction. Other threats include shoreline development, fishing nets, and pollution from shipping.

. . .

But Wan is a thief for conservation, not for profit.

"We at the hatchery are learning from experience and mistakes, and our hatch rates are very slowly improving," said Wan, coordinator at the Ma'a Daerah Turtle Center on Malaysia's remote east coast, one of few sites in the world where the fussy animals come ashore.

The waters of this Southeast Asian country are home to four of the world's seven sea turtle species - the giant leatherback, the green, the hawksbill and the olive ridley. All seven species are listed as endangered or threatened with extinction.

Accurate numbers, however, are almost impossible to calculate, as the turtles are migratory and hardly ever surface, making them hard to track. Only females come ashore - every two years, about four times a year - to lay eggs.

On shore is when the turtles are most vulnerable. If they survive egg hunters, 2-inch hatchlings emerge by the thousands and start a life-and-death scramble to the water's edge, easy prey for birds and other predators.

Conservationists say about 40 percent of hatchlings die in their first hours at sea, and only one in 1,000 survives the 50 years it takes to reach adulthood.

Most endangered is the giant leatherback, which conservationists say has declined by 99 percent since the 1950s. In one year back then, 2,000 turtles were reported to have come ashore to nest at Malaysia's Rantau Abang. Last year, there were about 10.

. . .

Conservation efforts began in earnest about 16 years ago, although government-run hatcheries existed as far back as the 1940s, said Abdul Rahman Kassim, coordinator of the Rantau Abang Turtle Sanctuary in Terrenganu state.

The handful of conservation centers in the state have released about 2.8 million turtle hatchlings into the sea during the past decade. It's not enough, officials say.

"We need to go further into total conservation - stop all egg consumption, strictly guard the coast, stop all beach development and fishing activities," Abdul Rahman said. "I feel we're only doing about 40 percent of that."

Lai Min Min of the Worldwide Fund for Nature in Malaysia said that because the males never leave the water, the only clues to what is happening to the species come from the females when they come ashore.

By the time a drop in the number of nesting females is noted, it's probably too late to address the cause, she said.

"We don't know where the hatchlings go, we don't see the males and the sub-juveniles. If anything happens to them we don't see it," she said. "When we see a decline, it is a sharp decline."

The Ma'a Daerah sanctuary is built on a milelong strip of untouched coast closed in by rocky, rain forest-clad hills and run by the WWF and Malaysia's Fisheries Department. It opened with a donation from a nearby British Petroleum refinery.

Arlene Hager, an activist and fund-raiser for the sanctuary, said the rutted, muddy road that is the only access to the beach will not be repaired - an attempt to keep onlookers away.

She said the key to preserving the turtle population at Ma'a Daerah is educating local fishermen to stop casting nets in protected waters and halt egg collection.

"This isn't an easy thing to control," she said. "There are laws against all this, but it is also the livelihood of the village folk we are talking about. It's a difficult issue - the conflict between man and nature."

This story can be found at : http://www.timesdispatch.com/frontpage/MGBYAF580VC.html

Does the acoustic deterrent work?

A number of studies with confined animals leads to a positive conclusion. However only now are there free ranging animals being exposed to the phase 1 portable prototype device

Stay tuned for updates!

 

...To participate in acoustic turtle trials please contact me at lenhardt@hsc.vcu.edu

 

Page Content and Design : Dr Martin L. Lenhardt
WebMaster: Alan G. Madsen
Last update: Sunday, January 27, 2002