For decades, tracking the tiny plankton meant sending research vessels out in the ocean, towing nets and counting samples by hand. Now, scientists are looking from above instead.
Using NASA satellite data, researchers found a way to detect Calanus swarms at the ocean surface in the Gulf of Maine, picking up on the animals' natural red pigment. This early-stage approach, described in a new study, may help researchers better estimate where the copepods gather, and where whales might follow.
Tracking the zooplankton from space could aid both the whales and maritime industries. By predicting where these mammals are likely to feed, researchers and marine resource managers hope to reduce deadly vessel strikes and fishing gear entanglements - two major threats to the species. Knowing the feeding patterns could also help shipping and fishing industries operate more efficiently.
"NASA invests in this kind of research because it connects space-based observation with real-world challenges," said Cynthia Hall, a support scientist at NASA headquarters in Washington. She works with the Early Career Research Program, which partly funded the work. "It's yet another a way to put NASA satellite data to work for science, communities, and ecosystems."
When large numbers of the zooplankton rise to the surface, their reddish pigment - astaxanthin, the same compound that gives salmon its pink color - subtly alters how photons, or particles of light, from the sun are absorbed or scattered in the water. The fate of these photons in the ocean depends on the mix of living and non-living matter in seawater, creating a slight shift in color that MODIS can detect.
"We didn't know to look for Calanus before in this way," said Catherine Mitchell, a satellite oceanographer at Bigelow Laboratory for Ocean Sciences in East Boothbay, Maine. "Remote sensing has typically focused on smaller things like phytoplankton. But recent research suggested that larger, millimeter-sized organisms like zooplankton can also influence ocean color."
A few years ago, researchers piloted a satellite method for detecting copepods in Norwegian waters. Now, some of those same scientists - along with Mitchell's team - have refined the approach and applied it to the Gulf of Maine, a crucial feeding ground for right whales during their northern migration. By combining satellite data, a model, and field measurements, they produced enhanced images that revealed Calanus swarms at the sea surface, and were able to estimate numbers of the tiny animals.
"We know the right whales are using habitats we don't fully understand," said Rebekah Shunmugapandi, also a satellite oceanographer at Bigelow and the study's lead author. "This satellite-based Calanus information could eventually help identify unknown feeding grounds or better anticipate where whales might travel."
"We've had whales getting hit by ships and whales getting stuck in fishing gear," said Laura Ganley, a research scientist in the Anderson Cabot Center for Ocean Life at the New England Aquarium in Boston, which conducts aerial and boat surveys of the whales.
In 2017, the National Oceanic and Atmospheric Administration designated the situation as an "unusual mortality event" in an effort to address the whales' decline. Since then, 80 North Atlantic right whales have been killed or sustained serious injuries, according to NOAA.
In the Gulf of Maine, there's less shipping activity, but there can be a complex patchwork of lobster fishing gear, said Sarah Leiter, a scientist with the Maine Department of Marine Resources. "Each fisherman has 800 traps or so," Leiter explained. "If a larger number of whales shows up suddenly, like they just did in January 2025, it is challenging. Fishermen need time and good weather to adjust that gear."
What excites Leiter the most about the satellite data is the potential to use it in a forecasting tool to help predict where the whales could go. "That would be incredibly useful in giving us that crucial lead time," she said.
MODIS is also nearing the end of its operational life. But NASA's next-generation PACE (Plankton, Aerosol, Cloud, ocean Ecosystem) satellite - launched in 2024 - is poised to make dramatic improvements in the detection of zooplankton and phytoplankton.
"The PACE satellite will definitely be able to do this, and maybe even something better," said Bridget Seegers, an oceanographer and mission scientist with the PACE team at NASA's Goddard Space Flight Center in Greenbelt, Maryland.
The PACE mission includes the Ocean Color Instrument, which detects more than 280 wavelengths of light. That's a big jump from the 10 wavelengths seen by MODIS. More wavelengths mean finer detail and better insights into ocean color and the type of plankton that the satellite can spot.
Local knowledge of seasonal plankton patterns will still be essential to interpret the data correctly. But the goal isn't perfect detection, the scientists say, but rather to provide another tool to inform decision-making, especially when time or resources are limited.
Research Report:Ocean color anomaly detection to estimate surface Calanus finmarchicus concentration in the Gulf of Maine
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