How Much do Pilot Whales Eat?

Researchers recently tagged eight shortfin pilot whales around the islands of Hawaii and followed them into the deep depths of the ocean where they feed, and what they found is truly unbelievable. Welcome back to Tea of the Sea, and found all around the world's tropic and subtropical oceans, the shortfin pilot whale is one of the largest oceanic dolphin species in the world. They are collectively part of the unofficial group of cetaceans known as the blackfish, which include orcas, both pilot whales, melon-headed whales, pygmy killer whales, and false killer whales. Like other dolphin species, shortfin pilot whales are incredibly social animals living in complex hierarchical family groups led by a female, and they are split into several distinct genetic populations around the world. And around the islands of Hawaii, there are an estimated 8,000 or so individual shortfin pilot whales split into three different population segments based on the areas around the islands that they're often found in. These seem to prefer certain regions, but like the rest of their species, they all have one thing in common in that they generally feed on squid, and they dive incredibly deep. There are a couple dozen cetacean species that will dive incredibly deep to feed on squid and deep-sea fish. Notably, these include the sperm whales and the beaked whales. But for oceanic dolphins, not a lot of them really do a whole lot of extreme deep dives for foraging purposes. Most oceanic dolphins will feed relatively close to the surface on large schools of fish. Shortfin pilot whales are one of the few oceanic dolphin species that will make extremely deep dives up to a thousand meters or more to hunt for food. This foraging strategy allows pilot whales to exploit a food resource that not a lot of the dolphins are utilizing, but it comes at a cost. For one, just the act of diving that deep comes with risks. Any scuba diver knows that there's a risk of decompression sickness when surfacing and a whole bunch of other problems that could arise. But the biggest risk for them is just the amount of energy needed to do those dives versus the amount of energy that they get from the dive. It's a high-risk strategy of foraging that requires a very delicate balance of the amount of energy used for the amount of energy that you get per successful hunt. And a new study by the Hawaii Institute of Marine Biology's Marine Mammal Research Program is the first step in quantifying that exchange of energy for this population of pilot whales. The study's lead author William Go along with the rest of his team tagged eight individual pilot whales with a special camera tracker that could visually record the dives as well as monitor movement, depth, speed, and sound to determine how much these whales were feeding. The team then used drone footage to measure the whales that were tagged to determine how much energy they were using as they swam around and made those deep foraging dives. And the study that comes out of this is the first of its kind to look at this energy usage for this population. So they could figure out how much energy the whales were putting into their daily activities and they could also use the data to figure out how much energy they're getting from each squid that they fed on to determine how much squid the population needed. Using all this data and plugging it into a computer, the team was able to determine that each adult pilot whale was on average feeding on anywhere between 80 to about 200 individual squid every single day. And since there's about 8,000 individual pilot whales in the Hawaiian population, the team was able to determine that the population needs to eat anywhere between 240 to 590 million squid every year. Now this information is incredibly important not just for the population but for the ocean and pilot whales and other cetaceans as a whole. If we're able to understand how much food a population or a species of cetaceans requires every year to survive, then that gives us a better understanding of what we can do to protect the populations in a changing world driven by human activity. Deep diving cetaceans like shortfin pilot whales can be especially vulnerable to human activities, specifically shipping noise and ocean heating brought on by human accelerated climate change. Boat noise can affect their ability to echolocate and hear where their prey is in the dark depths of the ocean and a warming ocean can disrupt food stocks forcing the whales to spend more time looking for food than they actually do eating that food. And of course if they are spending more energy looking for food than they are getting energy from the food, it's going to affect the population as they're not going to be as healthy, they're not going to be as fit, and they're not going to be able to effectively reproduce to sustain the population. This study is incredibly important because of those reasons and hopefully with this understanding we can do more to better protect the Hawaiian population shortfin pilot whales, the rest of their species worldwide, and the rest of the oceans as a whole in the near future.