New Research: Noisy Ocean Could Mean Hungry Orcas

Apr 22, 2015

Beneath the surface of the Pacific Ocean it can get pretty noisy.
Hundreds of big ships, barges, fishing boats and other vessels motor up and down the Northwest coast every year.
Some new research details how that noise could make life harder for endangered marine mammals.

Credit Melisa Pinnow / Orca Network and the Center for Whale Research

Picture yourself at a noisy bar. You realize that you have been shouting at the top of your lungs all night in order to be heard. Well, orcas in Puget Sound are in kind of the same situation.

This is a recording from a hydrophone that was suctioned on to a wild killer whale in the San Juan Islands, near a passing vessel.
Loud boat noise forces endangered killer whales to raise the volume of their calls.
Marla Holt is a biologist at the NOAA Northwest Fisheries Science Center.
Marla Holt: “But the question is, ok, so they do it, so what? What are the biological consequences of them doing this?”
To answer that question, Holt and her NOAA colleague, Dawn Noren, studied captive bottlenose dolphins.
The dolphin swims into this funny little floating plastic helmet-looking thing, that’s positioned over its head. Then the trainer asks it to make its normal whistling call for 2 minutes for a fishy reward:

Dawn Noren measured how much oxygen the dolphin used.
Dawn Noren: "And then by knowing oxygen consumption you can determine metabolic rate or how much it costs you to work, or work harder."
Then the trainer asked the dolphin to pump up the volume.

Making that louder call, takes more energy. Holt and Noren found that when the dolphin was whistling harder and louder its metabolic rate rose by up to 80% above normal resting levels.
When their metabolic rate goes up, they burn more calories, so they have to eat more.
Dawn Noren: “If you have multiple incidences where you’re increasing your vocals to compensate for a noisy environment, you could have some increased need to find more fish.”
The scientists say that when wild orcas are around loud ships, the volume of their calls increase by the same amount, or more, than the dolphins in the lab.
That could mean wild orcas need to eat more salmon to make up for the calories they’re burning to vocalize louder around big ships.
Marla Holt: "The concern is that for animals that are maybe just getting by or not really getting by, we could say, this is how much more fish it would cost an animal if it was disturbed that much more."
Holt says that as the region considers proposals to expand coal and oil shipments, as well as Navy training activities, this research could be used to calculate specific impacts on marine mammals like endangered killer whales. There are just 81 of them left.
 

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