Blue whales follow their prey as ocean conditions change

A new study from Oregon State University has revealed that global warming influences the distribution of blue whales by altering ocean conditions and the availability of prey.

The research was focused on a population of blue whales that was recently discovered by the OSU team in New Zealand. 

Professor Leigh Torres is the director of the Geospatial Ecology of Marine Megafauna Laboratory at the Marine Mammal Institute.

Understanding how changes in climate affect the ability of blue whales to feed gives researchers more insight into the whales’ overall health and provides critical information for conservation and management, explained Professor Torres.

“These whales don’t move around at random. We found that the same ocean patterns that determine where whales are also determine where their prey are, under both typical and warm ocean conditions.” 

“The more we learn about what drives these whales’ movement, the more we can help protect them from whatever threats they face.”

The new whale population documented by the researchers was found to be genetically distinct from other blue whales. The group lives primarily in the South Taranaki Bight between New Zealand’s North and South Islands.

Study lead author Dawn Barlow is a doctoral student in the lab of Professor Torres.

“The goal of our study is to understand the habitat use patterns of this population of blue whales – why they are where they are and how they respond to changing ocean conditions,” said Barlow. 

“We know this area is important to this population of whales, and we want to understand what it is about this spot that is desirable to them.”

The region often has an abundance of krill, which is the blue whale’s preferred food, but the numbers of krill fluctuate alongside ocean temperature and composition. 

The South Taranaki Bight also sees frequent shipping traffic and activity from oil and gas exploration and production, noted Professor Torres.

The study was focused on data collected during average summer conditions in 2014 and 2017 and warmer than average conditions in 2016. 

The researchers used the data to analyze how changing ocean conditions affect blue whale distribution and the location of their prey.

The study showed that during a marine heat wave in 2016, there were fewer aggregations of krill available for blue whales. 

Barlow explained that with fewer options, the whales pursued the densest aggregations of krill they could find.

The research also revealed that during both warm and typical ocean conditions, the whales were more likely to feed in areas where the water was cooler. 

In the South Taranaki Bight, cooler water temperatures represent deeper, nutrient-rich water that was pushed toward the surface in a process called upwelling, explained Professor Torres.

This explains why blue whales are drawn to the cooler water – it provides nutrients that support large numbers of krill.

According to Professor Torres, the findings can be used to inform and adjust the management of human activities in the region to reduce impacts on New Zealand blue whales.

“Documenting information like this can really help us understand how to reduce threats to these animals,” said Professor Torres.

“We need continued monitoring to understand how these whales will respond to both the changing climate and human impacts.”

The study is published in the journal Marine Ecology Progress Series.

—

By Chrissy Sexton, Earth.com Staff Writer