Nav: Home

Researchers map how marine mammals interact with their prey

March 02, 2016

A team led by Purnima Ratilal-Makris, associate professor in Northeastern's Department of Electrical and Computer Engineering, has mapped a mass feeding frenzy involving more than eight highly protected species of whales and dolphins in the U.S. Gulf of Maine region. It is the first time researchers have observed predator and prey interactions in the wild over such a vast expanse, including specific species' feeding behaviors. Understanding how the two relate could have important implications for conserving marine ecosystems.

The research, published in the journal Nature, is especially timely given concerns about climate change, including how water temperature, pollution from land runoff, overfishing, and other alterations affect life in ocean environments.

Ratilal-Makris and her colleagues use innovative underwater acoustic sensing methods to access crucial information that policymakers and marine managers can use, she says, "model ocean ecosystems and formulate regulations for effective management of human activities in the ocean."

Ratilal-Makris and her team have been at the forefront of oceanic monitoring for decades. In two earlier papers published in Science, they described a new technology for mapping fish, including the Atlantic herring many whale species favor, and the remarkable convergence at night of billions of herring into shoal formations, each the size of Manhattan, on the northern flank of George's Bank, where the fish go to spawn.

Called ocean acoustic waveguide remote sensing, or OAWRS, the technology comprises a densely sampled hydrophone array--essentially a long insulated electrical wire with 160 underwater microphones attached to it. The system surveys an area of an astonishing 100,000 square kilometers and instantaneously returns images derived from projected sound scattered by the herring's air-filled bladders back to the researchers aboard the ship.

In the new study, Ratilal-Makris paired OAWRS with POAWRS, or "passive OAWRS," over a two-week span. The technology uses the same hydrophone array to pick up and record calls of various marine mammals and then maps the animals' locations and pinpoints their species.

POAWRS took almost six years to develop, says Ratilal-Makris. "We had to learn all the different sounds that marine mammals produce, what was unique to each species, and then create a methodology using the hydrophone array not only to detect the sounds but to locate what direction they were coming from and their distance from us," she says. They also had to construct a "classifier" to match the vocalizations to the individual marine mammal species. Among those the system tracked: blue, fin, humpback, sei, minke, sperm, pilot, and killer whales and a variety of dolphins, each with its own unique call pattern.

The humpbacks' vocalizations, lyrically, tipped into song. "As with human songs there are themes that repeat," says Ratilal-Makris. "We recorded many of their repeated themes--some went on for hours."

A feeding frenzy may bring disparate groups together at once, circling their common "prey," but that doesn't mean they necessarily dine together.

The whales arranged themselves around the herring shoals, she explains, in "species-specific foraging centers with varying degrees of overlap." That meant a "hotspot" for the humpback whales here, a "hotspot" for the minke whales there, yet another for the fin whales, and so on.

"Before this work, nobody knew how the different whale species organized in relation to their fish prey," says Ratilal-Makris. "Our study shows that they are not all mixed evenly--there are really well-defined feeding centers for each species." What does that mean? "Perhaps they want to stick to their own kind," she says.

It's a question she will explore in subsequent research. Another next step, says Ratilal-Makris, is to develop the means to make more precise "abundance estimates." "We can identify the direction and location of the sounds of the various species, but so far we can't estimate size of the populations very accurately," she says.

Knowing the species' whereabouts, as well as their growth and reduction in relation to environmental changes, would help scientists better identify, and respond to, sources of ecosystem imbalance.

"What the study provides is exciting new insight into a previously hidden world," explained one of the paper's academic reviewers. "I think this manuscript is ground-breaking."
-end-


Northeastern University

Related Dolphins Articles:

Lights on fishing nets save turtles and dolphins
Placing lights on fishing nets reduces the chances of sea turtles and dolphins being caught by accident, new research shows.
Genes 'lost' in whales and dolphins helped their ancestors transition to life underwater
When cetaceans (whales, dolphins, and porpoises) transitioned from life on land to life in the sea about 50 million years ago, 85 genes became inactivated in these species, according to a new study.
Antibiotic resistance surges in dolphins, mirroring humans
Scientists obtained a total of 733 pathogen isolates from 171 individual wild Bottlenose dolphins in Florida and found that the overall prevalence of resistance to at least one antibiotic for the 733 isolates was 88.2%.
Environment: Pollutants found in skin and blubber of English Channel dolphins
High levels of pollutants, such as industrial fluids and mercury, may have accumulated in the blubber and skin of one of the largest coastal populations of dolphins in Europe, a study in Scientific Reports indicates.
Dolphins form friendships through shared interests just like us, study finds
When it comes to making friends, it appears dolphins are just like us and form close friendships with other dolphins that have a common interest.
Climate change threat to dolphins' survival
An unprecedented marine heatwave had long-lasting negative impacts on both survival and birth rates on the iconic dolphin population in Shark Bay, Western Australia.
Stranded dolphins have amyloid plaques in their brains
Dolphins stranded on the beaches of Florida and Massachusetts show in their brains amyloid plaques, a hallmark in human beings of Alzheimer's disease, together with an environmental toxin produced by cyanobacterial blooms.
Male bottlenose dolphins form bachelor groups with their relatives
New research has analysed the behaviour of 12 dolphin social groups in South Australia's Coffin Bay region and shows males who team up in groups of two to five to form beneficial alliances may have more success.
Radio-tracking dolphins reveals intimate details about their behavior
The most extensive radio-tracking effort of bottlenose dolphins in the Indian River Lagoon using radio-telemetry reveals new and surprising information about how they use their habitats, how they spend their time, and how they interact with their own species.
Plastic in Britain's seals, dolphins and whales
Microplastics have been found in the guts of every marine mammal examined in a new study of animals washed up on Britain's shores.
More Dolphins News and Dolphins Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

In & Out Of Love
We think of love as a mysterious, unknowable force. Something that happens to us. But what if we could control it? This hour, TED speakers on whether we can decide to fall in — and out of — love. Guests include writer Mandy Len Catron, biological anthropologist Helen Fisher, musician Dessa, One Love CEO Katie Hood, and psychologist Guy Winch.
Now Playing: Science for the People

#543 Give a Nerd a Gift
Yup, you guessed it... it's Science for the People's annual holiday episode that helps you figure out what sciency books and gifts to get that special nerd on your list. Or maybe you're looking to build up your reading list for the holiday break and a geeky Christmas sweater to wear to an upcoming party. Returning are pop-science power-readers John Dupuis and Joanne Manaster to dish on the best science books they read this past year. And Rachelle Saunders and Bethany Brookshire squee in delight over some truly delightful science-themed non-book objects for those whose bookshelves are already full. Since...
Now Playing: Radiolab

An Announcement from Radiolab