Scientists have found the Weddell seal uses a dive timing strategy to optimize its foraging options.
The study found that seals opt to conduct more extreme, deeper dives earlier in the day when there is less light and fewer prey around.
The strategy is straightforward: Since longer, deeper dives require more recovery, the seals perform them earlier in the day and when there is less prey around. This means they are not wasting prime feeding time recovering. Later in the day, when there is more light and more abundant prey, they conduct shallower, easier dives that can repeated frequently to optimize feeding opportunities.
According to Woods Hole Oceanographic Institution assistant scientist in Biology and study lead author Michelle Shero:
“These extreme dives require longer recuperation times once the seals return to the surface. So, if the seals make extreme dives in the middle of the day when it is maximum light — there may be lots of prey around that are easy to see, but the seals would still ‘miss out’ because they’d have to spend a lot of time recuperating. Not conducting extreme dives when prey is most accessible, may actually be the best strategy.
“We are seeing these animals through a whole year when it’s daylight 24/7, a combination of daytime and nighttime, and then dark 24/7, providing a ‘natural experiment’ to better understand how the seals’ feeding strategies change with a range of light conditions. During peak daylight hours, almost all animals including the seal’s prey will descend deep into the water column to avoid predation. We expected that the seals would follow their food and that their deepest, longest dives might occur at midday when the sun is overhead. But what we surprisingly found was that the seals appeared to actually avoid making their most extreme dives during midday…allowing the seals to keep diving over and over without having to pause for long.”
Check out the research at nature.com.
