This Whale’s Meal Plan? Over 70,000 Squid A Year, And It’ll Dive Incredible Depths To Get Them

How much do you need to eat to stay alive and healthy? It's an interesting question and one that is crucial to protecting a lot of Earth’s species. For short-finned pilot whales, the answer is somewhere between 82 and 202 squid per day, which scales up to as many as 73,730 squid per year, and for the entire 8,000-strong population, more than 589 million squid in total.

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Short-finned pilot whales (Globicephala macrorhynchus) are an understudied species of oceanic dolphin that have a population that lives in the waters around Hawaii. To learn more about their behaviors, dietary habits, and energy requirements, the team used suction cup tags deployed onto the short-finned pilot whales to collect data.

"Ideally, we attached the tag right behind the blowhole facing the head, so we could see any foraging at depth," said study author William Gough from the University of Hawaiʻi at Mānoa in a statement.

The pilot whales can dive to depths of 1,700 meters (5,577 feet) as they forage, something that is incredibly energetically demanding. As mammals, they then have to return to the surface to breathe. The team learnt from the tag data that the whales were diving as many as 39 times a day. These dives lasted between 8-16 minutes and were of an average depth of 400-800 meters (1,312-2,625 feet). 

Using whale tail beats as a proxy for their energy consumption, the team found out that they use 73.8 kilojoules per minute (kJ/min) of energy while diving and around 44.4 kJ/min of energy at the surface of the water. They then translated this into the number of squid that needed to be consumed per whale to meet these energy costs. 

Using hydrophone recordings, the team could tell when the pilot whales intercepted a squid on a dive; they worked out that roughly four squid were consumed per dive, and each squid provided 560kJ of energy to the whale. Knowing this and the energy expenditure, the team then calculated that each whale must eat between 82-202 squid per day and around 73,730 squid per year. This also means that the total population of pilot whales in this area consumes around 88,000 tonnes of squid per year. Fortunately, the squid population in Hawaii is well able to support this. 

"These results show that short-finned pilot whales are in relatively good shape in Hawaiʻi, having found an abundant and reliable source of food," said Gough.

The study is published in the Journal of Experimental Biology.