Follow the food to find the right whale

For years, conservation scientists have struggled to predict the locations of critically endangered North Atlantic right whales, often relying on models of environmental signals to estimate their movements.

But understanding where and why these whales travel is critically essential as interest groups and researchers work to reduce deadly entanglements with lobster gear and collisions with vessels —two of the leading causes of right whale deaths on the east coast of the United States.

Now, after years of uncertainty, scientists may have found a breakthrough by mapping the distribution of key zooplankton prey.

“This makes sense ecologically,” said Camille Ross, an associate research scientist at the New England Aquarium’s Anderson Cabot Center for Ocean Life. “Right whale distributions are likely prey-driven, so increased abundance of [certain zooplankton] in a region should theoretically lead to higher right whale density, assuming whales can detect those high-density prey patches.” 

Researchers are gaining a clearer picture of the whales’ movements, renewing hope in managing one of the United States’ most imperiled species.

ID by land and by sea

North Atlantic right whales (Eubalaena glacialis) were hunted to the brink of extinction in the 20th century by the whaling industry. Even though that ended decades ago, late maturity has delayed recovery. Contemporary recovery is also hampered by ship strikes and entanglement in fishing gear—prominent causes of whale death.  

To help facilitate recovery and mitigate human-caused death, researchers have monitored the species extensively from birth for decades. Pilots fly systematic track lines over known whale habitats, photographing and recording individuals from above, while research vessels collect additional sightings and environmental data from the water’s surface. Despite this work, gaps remain as researchers can’t be everywhere at once. Surveys cover limited areas and times of year. Spotting whales can be dependent on weather, equipment, and whale behavior.

In the past, researchers have relied on chlorophyll-a as a proxy for whale food to help predict where the species was likely to be. Chlorophyll-a is a green pigment used by tiny plant-like organisms called phytoplankton for photosynthesis. Researchers used the amount of the pigment detected by satellites to measure the amount of phytoplankton. Zooplankton, small oceanic organisms, eat phytoplankton. Previous models assumed that more phytoplankton would mean more zooplankton, which would then attract the whales.

A new perspective

After years of relying on broad environmental indicators like chlorophyll-a to estimate where endangered North Atlantic right whales might appear, researchers are now taking a more targeted approach that focuses on the ocean features that matter most to the whales themselves: the distribution of their prey.

In a joint effort between the Anderson Cabot Center, the Bigelow Laboratory for Ocean Sciences and the University of Maine published in Endangered Species Research, Ross and her collaborators used statistical models to combine whale sightings with environmental variables and data on three zooplankton prey species: Calanus finmarchicus, Centropages typicus and species of the genus Pseudocalanus.

By incorporating these three species that the right whales eat, the models better predicted right whale movements than those that included chlorophyll-a more generally. In other words, by linking whale sightings directly to their prey, scientists can more accurately predict where the animals are likely to appear, in hopes of mitigating conflicts and understanding their movement in a changing ocean.

Looking to the future

Historically, Cape Cod Bay and the Great South Channel have been crucial feeding grounds for whales, particularly in late winter and spring. However, the timing and intensity of prey availability are shifting in response to climate change. “The timing of habitat use is just becoming less predictable than it was in the early 2000s,” said Ross. “That’s why models like this are so valuable; they help managers adjust as conditions change.”

While this study focuses on past and current patterns, researchers could expand future models to forecast whale distributions under climate change scenarios, thereby aiding in the management of North Atlantic right whales.