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Devices reveal some undersea surprises

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    An electronic satellite transmitter is visible on a tiger shark. Studies of the sharks around Maui, Molokai and Lanai have shown that they roam nearshore reefs more often than previously believed.
    Electronic tracking devices, attached at the surface, are giving marine biologists a glimpse into the habits of sea life, both in the deep ocean and in nearshore waters.

Sophisticated electronic tracking devices are giving marine biologists an important glimpse at the behavior of both common and endangered species as the oceans respond to climate change and other human influences.

“We’re seeing behaviors we had no idea existed,” said University of Hawaii researcher Kim Holland in a telephone interview Wednesday.

For instance, satellite telemetry in combination with acoustic tagging has also enabled scientists to find out that yellowfin tuna can sometimes swim below 3,000 feet — a depth that came as a surprise to scientists.

And studies of tiger sharks around Maui, Molokai and Lanai have shown that they frequent near-shore reefs more often than previously suspected.

The advances in tracking are described in a research paper, “Aquatic animal telemetry: A panoramic window into the underwater world,” published online June 12 in the journal Science.

The review, co-written by Holland, a shark expert with the Hawaii Institute of Marine Biology, describes a revolution in global ocean observation science achieved through advancements in acoustic and satellite telemetry. Lightweight tags placed on the animals — from tiny newborn fish to whales — transmit data either to fixed or mobile receiver stations or satellites.

Typically, they record position, depth, temperature and salinity.

Electronic tags can now weigh less than a penny, can transmit for more than 10 years and can be attached to almost any species, at any life stage — allowing the monitoring of organisms whose habitats range from the poles to the tropics and from sun-bathed shallows to inky depths.

“The vastness and impenetrability of the ocean has historically limited our ability to acquire and process information on animal movements,” said Sara Iverson, co-author of the paper and a professor at Dalhousie University in Halifax, Nova Scotia, in a release Tuesday. “Telemetry has significantly enhanced our capacity to predict and plan in the face of climate change and human influence.”

Holland said tracking of aquatic animals is rapidly expanding with a potential of becoming part of a global network — the ultimate “big picture” of how species interact, or don’t, in the ocean.

“There are experiments going on all over the world,” said Holland.

Telemetry data have revealed the often mysterious migrations of endangered marine animals such as leatherback turtles, basking sharks, European eels and Pacific bluefin tuna. Tagging has also shed light on the habits of the southern rock lobster, lemon shark, green seal turtle and gray seal.

While most tags upload data only when near the surface, others can detach after a time and rise to the surface on their own.

That allows scientists to track fish that prefer the depths.

“You can reconstruct the path of an animal that has never come to the surface,” Holland said.

The tags must be attached at the surface, however.

For tiger sharks, that involves flipping them on their backs, which puts them into a pliant state.

Holland said he’s been tracking the movements of both deep-ocean and nearshore fishes and trying to relate their movements, home range sizes and swimming strategies to their foraging.

The discovery of ocean animal patterns also is expected to improve resource management.

The authors conclude, “These advances provide the toolbox to define how future global aquatic management practices must evolve.”

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