How Salmon Sharks Help Us Understand Climate Change

Since the early 2000s, the amount of ocean data collected has surged, providing scientists with critical insights into climate change and ocean variability. This increase is largely thanks to the deployment of thousands of Argo floats, which now cover oceans globally. These robotic sensors have provided over two million temperature-salinity profiles, yet gaps remain, particularly in remote areas like polar and coastal regions. To fully understand the changing ocean, scientists need more data from these under-sampled locations. The Gulf of Alaska is one such region, where climate change is expected to have pronounced effects. While traditional monitoring tools are useful, they can’t be everywhere at once.

That’s where the marine life comes in. Yup, they’re doing science!

Elephant seals have been fitted with tags that measure temperature, salinity, and depth, helping to fill these observational gaps in hard-to-reach waters. Since 2002, data from tagged seals has transformed our understanding of ocean currents, sea ice formation, and submesoscale processes — small but crucial movements of water that influence larger climate patterns. Now, researchers are expanding this concept to sharks. Large, non-air-breathing marine animals, such as salmon sharks (Lamna ditropis), are frequently tagged with satellite transmitters that record depth, temperature, and movement. These sharks dive deep and travel far, making them ideal for collecting oceanographic data in regions where other tools fall short.

A new custom-built tag, called a CTD-SRDL, was designed to fit on a salmon shark’s dorsal fin, allowing researchers to track temperature and salinity profiles while following the shark’s natural movements. In 2015, a 5-foot-long salmon shark was tagged in Port Gravina, Alaska, with one of these devices and for over 36 days, the shark traveled more than 840 miles, transmitting 56 detailed temperature-salinity profiles via satellite. The shark’s journey provided a unique opportunity to examine ocean conditions during a particularly significant event: the Blob. This massive patch of unusually warm water appeared in the northeast Pacific in late 2013 and lasted until 2016, causing widespread disruptions to marine ecosystems.

The data collected from the tagged shark confirmed that most of the water it traveled through was warmer than average. Nearly 75% of the temperature readings showed positive anomalies, with some areas registering more than 3°F (1.5°C) above normal. These warm anomalies were most pronounced at depths of around 65 feet (20 m), especially off the coast of Sitka, Alaska. However, the shark also encountered pockets of colder water, typically closer to the coast and in deeper layers. Salinity measurements were more variable, with some areas showing saltier-than-average conditions while others were fresher. Interestingly enough, the strongest fresh anomalies were recorded in northern sections of the shark’s journey, while saltier waters dominated farther south.

One of the most intriguing finds came from the shark’s encounters with mesoscale eddies — large rotating bodies of water that can influence ocean circulation and heat distribution. Over its journey, the shark moved through seven of these eddies, capturing detailed profiles of their temperature and salinity structures. Some eddies trapped warmer, saltier water near the surface, while others had pockets of cold, fresh water at different depths. These observations, the scientists say in their publication, allows for a better understanding on how heat and salinity move through the ocean, influencing larger climate patterns.

The data collected from this shark was then compared to information from Argo floats in the same region. And while both sources provided valuable insights, it turns out that the shark’s data had a much higher resolution in certain areas (especially in dynamic regions influenced by eddies and coastline interactions). If all salmon sharks tagged in the Gulf of Alaska over the past 17 years had been equipped with these specialized CTD tags, the team estimates that the number of high-resolution ocean profiles from this region would have been significantly higher, providing a much clearer picture of ocean conditions.

Yes, 'hiring’ sharks to be oceanographers is still in its early stages, but the potential is enormous. Unlike robotic floats, sharks naturally navigate areas of interest, following temperature gradients, prey movements, and ocean currents. They can reach depths and locations that traditional sensors struggle to access! By expanding tagging efforts and refining the technology, researchers hope to integrate shark-collected data into global ocean monitoring systems, complementing existing tools like Argo floats.

Understanding ocean variability is crucial for predicting climate change, managing fisheries, and conserving marine ecosystems. The oceans are changing rapidly, and some of the most important shifts are happening in regions where data is scarce. By turning to nature for help, the future of ocean monitoring may be swimming right in front of us.