Researchers are hoping a technique that identifies zooplankton from space will eventually help them track the movement of critically endangered North Atlantic right whales in the Gulf of Maine.
Scientists at the Bigelow Laboratory for Ocean Sciences in Maine are using NASA satellite data to attempt to identify Calanus finmarchicus, the tiny zooplankton that are the main food source of North Atlantic right whales.
The zooplankton, which are smaller than a grain of rice, contain a reddish pigment — the same pigment that makes salmon look pink. When large quantities of the creatures congregate at the water’s surface, that pigment affects the spectrum of sunlight that is absorbed and reflected, and the satellite can detect the resulting colour shift.
The researchers hope that by tracking the presence of zooplankton, they will someday be able to predict the movement of North Atlantic right whales, and hone attempts to protect them.
“The Gulf of Maine conditions have been changing. They’ve been rapidly warming. And we believe that means their main food source has moved to a different location,” says Catherine Mitchell, a senior research scientist at the Bigelow Laboratory and co-author of a new study about the ocean colour technique.
“So if we know where the whales are, it could help inform the conversation around their conservation.”
North Atlantic right whales are nearing extinction, with only about 370 remaining, and only about 70 breeding females.
After 17 dead whales were identified in Canada and the United States in 2017, Canada implemented restrictions on fishing and ship speeds in certain areas of the Atlantic region to prevent further deaths due to vessel strikes and entanglements in fishing gear.
Knowing where the whales are, and where they might go, could help governments more efficiently use fishing closures or vessel speed restrictions to protect them.
The Bigelow Laboratory researchers got the idea of using the satellite data to try to find Calanus finmarchicus from a previous study that was done off Norway.
But when they started reviewing the data from the Gulf of Maine dating back to 2003, they noticed something unusual.
“We were detecting patterns out of the season when we would expect to see Calanus finmarchicus, which made us realize that we were seeing other things too,” Mitchell said.
The model was picking up not just Calanus finmarchicus, but other zooplankton that contain the same red pigment. Mitchell and Rebekah Shunmugapandi, lead author and post-doctoral scientist at the Bigelow Laboratory, are now trying to refine their method to try to pinpoint the North Atlantic right whale’s favourite food species.
Shunmugapandi is working to validate some of the satellite data with in-the-water observations from researchers in the Gulf of Maine as well as actual right whale sightings.
“They move along with their prey, right?” Shunmugapandi said. “So with all those in situ Calunus and the right whale sighting data set … it’s kind of a reverse study that I’m doing.”
One potential solution to differentiating Calanus finmarchicus from other red-pigmented zooplankton could be orbiting the Earth right now.
The researchers have so far relied on data from NASA’s Aqua satellite, but the instrument used to capture the light spectrum, MODIS, is nearing the end of its lifespan. However, NASA’s newer PACE (Plankton, Aerosol, Cloud, ocean Ecosystem) satellite, which was launched last year, could vastly improve scientists’ abilities to analyze ocean colour.
Aqua’s light-detecting instrument identifies 10 wavelengths of light. The researchers used only three of its wavelengths for their study.
The new instrument aboard PACE, called the Ocean Color Instrument, can detect 280 wavelengths.
Shunmugapandi says researchers would need to develop a new computer model to analyze a wider spectrum of light.
“The hope is that with much more wavelengths, we might be able to tease out some more things, particularly things actually like the different species,” Mitchell says.
Currently, zooplankton researchers attempt to identify and track species by collecting them in nets to examine, using video cameras that function as underwater microscopes, and studying acoustics in the water.
Catherine Johnson is a research scientist at Fisheries and Oceans Canada who specializes in zooplankton ecology.
She says quantifying and identifying zooplankton is difficult because the ocean is so vast and their distribution is variable over space and time. Most sampling techniques work best when they’re focused in a specific area or time frame.
Johnson, who was not involved in the new study, says remote sensing of zooplankton could be a tool in the toolbox of scientists.
“It has the potential to provide good coverage over space and time if you’re looking for exceptionally dense and large aggregations that are right near the surface,” she said.
“It’s one piece of the puzzle, and I think that the study is a proof of concept to try to apply these methods in an area where they haven’t been applied before.”
Mitchell and Shunmugapandi agree there’s lots more work to be done.
“Science is a process and we’re not saying that this satellite product we’ve made is the be-all and end-all answer to understanding where right whales are,” says Mitchell. “We are just trying to provide an extra piece of information that could be useful to the story and helpful to people.”
