New research from the Woods Hole Oceanographic Institution (WHOI) and partners reveals that Weddell seals that inhabit the icy waters of Erebus Bay, Antarctica, employ a careful hunting strategy when it comes to diving, timing their dives to balance energy use and foraging efficiency.

The study, published in Communications Biology, shows that the seals perform their longest and deepest dives early in the day, and not during midday when sunlight is at its peak. 

This is because hunting during midday would have required longer recovery periods on the surface, which can in turn adversely affect foraging behaviour. Thus, by diving intensely earlier in the day, the seals maximise their time underwater and reduce the amount of time spent recuperating on the surface.

The scientists came to this conclusion after collecting and studying 8,913 days of dive information from 59 adult Weddell seals in the Ross Sea that were fitted with data loggers. The data provided a detailed look at how the seals balance oxygen conservation with energy gain from prey capture. 

Strategic thinking

Michelle Shero, lead author and WHOI scientist, elaborates on the seals' strategic approach. During peak light hours, most animals (including the seals’ prey) descend deeper to avoid predators. Yet, instead of pursing their prey and diving their deepest dives at midday, the seals actually avoided making such dives during this time. 

“Not conducting extreme dives when prey is most accessible, may actually be the best strategy,” she said. This strategy allows the seals to hunt consistently, balancing their need for oxygen with their search for food.

“These animals are making very strategic decisions about when to make their long dives, so they can best interact with the daily changing environment in the Antarctic, allowing them to maximise their prey,” she added.

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