OSU professor takes cue from dolphins

Published 4:00 pm Wednesday, March 10, 2010

One of scientists’ biggest barriers to studying animals in the ocean is a lack of visibility underwater.

But Kelly Benoit-Bird, an associate professor at Oregon State University’s School of Oceanographic and Atmospheric Sciences, has a way around that obstacle.

She’s taking a cue from dolphins, which use acoustics to communicate and navigate in the ocean.

Benoit-Bird spoke to a crowd of about 80 at the Columbia Forum in Astoria Wednesday about her research using high-frequency sound to study the behavioral patterns of ocean life as small as zooplankton and as large as whales.

Her studies help explain the connection between anchovies and sardine migration and salmon survival, how spinner dolphins help each other survive on 2-inch lantern fish and how giant Humboldt squid can eat just about anything.

Acoustic technology sends out sound signals that move through the water, bounce off animals and send information back about the size, shape and movements of marine creatures.

Benoit-Bird is using acoustics primarily to learn about the feeding habits of animals in the ocean.

Food is scarce resourceOverall, she said, less than 1 part per million of the ocean is food.?At most, in highly concentrated feeding grounds, it might be 2 parts per million.

“Food in oceans is a pretty scarce resource,” she said. “And obviously, food is the currency of survival for these organisms. One of the questions we’re looking at is: How are they able to survive on these small amounts of food without becoming food for someone else?”

The acoustics Benoit-Bird uses to track and study sea life are a lot like a standard fish finder used by recreational fishermen, but they’re “much, much more sensitive,” she said. They’re calibrated so scientists can get numbers and not just images on their screens.

They allow scientists to gauge how many fish are in a school, and track interactions between individuals.

Sonar devicesBenoit-Bird has left sonar devices anchored to the sea floor for four to five months collecting data once every second. The result is a clear picture of what is moving back and forth across that position over time.

An image taken off the coast of California shows zooplankton as “diffuse blue speckly stuff” and anchovies are “very intense red balls.”

One of Benoit-Bird’s studies off the West Coast shows that schools of sardines and anchovies wait for specific water temperatures before migrating north. Then they all move at once – instantly creating a critical food source for out-migrating salmon.

“There’s nothing else for salmon to eat if the sardines and anchovies aren’t present,” she said. “The presence of that food source changes their survival from 10 to 20 percent to less than 1 percent.”

Using multibeam sonar – with 120 beams instead of just one – Benoit-Bird can create videos of animal movements from multiple angles. The technology has allowed her to document the size, shape and distribution of the ocean’s plankton – tiny photosynthetic creatures the size of a rice grain – and how other creatures interact with them. What she found is in some areas 95 percent or more of the ocean’s plankton is found in just a few inches of water, forming a virtual “salad bar” for other creatures to feed on.

Benoit-Bird showed the group a video illustrating a salmon methodically eating a hole through a layer of plankton, changing their formation from “a pancake” to more like “Swiss cheese.”

The jumbo Humboldt squid has recently shown itself to be an invading species on the West Coast. It grows quickly, can get up to 5 feet in length, and its range is rapidly expanding northward.

For a long time, scientists thought sonar technology wouldn’t be able to track the squid, but Benoit-Bird conducted controlled tests on captured Humboldts that allowed her to identify the acoustic signature of the animal.

“It turns out they’re fantastic sonar targets,” she said.

She’s also documented how they move around to feed in shallow and deep water depending on where their food sources are and how they cluster tightly into piles with as many as 15 squid per cubic meter. They can eat fish as large as themselves, pluck seabirds directly from the surface of the water, and they’ll even eat each other.

“They’re an extremely flexible predator,” she said. “This really suggests we have a lot to learn. It’s difficult to predict what their ecosystem impacts might be. … They’re like the vacuum cleaners of the ocean.”

Another benefit of the sonar technology is comparing daytime feeding patterns with what happens at night – when it’s even harder to collect traditional data on sea creatures.

“Everything changes when the sun goes down,” she said.

Benoit-Bird has used sonar to document the nighttime feeding habits of spinner dolphins in the central Pacific ocean, illustrating an orchestrated group movement to encircle and concentrate pools of 2-inch lantern fish for easier feeding.

During the day, the spinner dolphins socialize near shore where it’s easier to spot their predators. They wait for illuminated lantern fish to migrate toward the water’s surface at night and then they collectively move out to feed.

The dolphins have a limited amount of time to feed on the lantern fish and high energy needs to satisfy. To survive, “they need to eat an awful lot of those fish,” said Benoit-Bird. “It would be like us trying to survive on popcorn that’s constantly moving away from us.”

Her sonar tracked the pod of dolphins pairing up and swimming in a circular formation to herd their prey into dense patches. Then, one by one, they took turns feeding in the thickly pooled food. But they only had about five minutes to complete the exercise before they all had to return to the surface for air.

To coordinate the movements, Benoit-Bird noted, the dolphins used their own form of sonar communication to line themselves up and arrange the circular swimming pattern.

Without employing similar sonar techniques, scientists wouldn’t be able to document this nighttime phenomenon, she said.

“We rarely get a chance to see them at night except on calm seas with a full moon,” she said. “The use of sound has allowed us to see how it works.”