Short-finned pilot whales (Globicephala macrorhynchus ) off the coast of Hawaiʻi require substantial daily squid intake to survive, but new research confirms that current squid populations can sustainably support them. This finding is critical for conservation efforts, as understanding food needs is fundamental to protecting vulnerable marine species.
The Challenge of Quantifying Food Intake
Determining how much food an animal consumes daily is essential for assessing its risk when food supplies dwindle. Pilot whales, known for deep dives reaching 1,700 meters in pursuit of squid, presented a particular challenge due to the difficulty of observing their feeding behavior in the wild.
Innovative Tracking Methods
Researchers from the U.S., Spain, Australia, and Denmark collaborated to solve this riddle. Led by William Gough (University of Hawaiʻi at Mānoa), the team deployed data-collecting tags with suction cups onto eight short-finned pilot whales. These tags included motion sensors, underwater cameras, hydrophones to record echolocation clicks, and GPS trackers.
The team also used drones, hovering 25 meters above the whales, to determine their size. Retrieving the tags, which sometimes drifted up to 50 miles after detaching, revealed that the whales made an average of 118 deep dives per day, reaching depths of 864 meters.
Energy Expenditure and Squid Consumption
By analyzing the whales’ tail beats during dives, the researchers calculated that they expend 73.8 kJ/min underwater, compared to 44.4 kJ/min at the surface. Listening for the distinct echolocation clicks that signal squid capture, they estimated that each whale consumes approximately four squid per dive.
Each squid provides around 560 kJ of energy when digested, leading to the calculation that individual whales must consume between 82 and 202 squid daily, totaling 73,730 squid per year.
Population-Level Impact
With an estimated population of 8,000 short-finned pilot whales around Hawaiʻi, the team calculated that the entire population consumes approximately 88,000 tons of squid annually. Fortunately, this represents a sustainable level of consumption for the local squid population.
Implications for Conservation
“These results demonstrate that short-finned pilot whales are in relatively good shape in Hawaiʻi, with access to an abundant and reliable food source,” says Gough. This finding suggests that the species is currently thriving in these waters, but continued monitoring is essential to ensure long-term sustainability.
The study underscores the importance of understanding predator-prey dynamics in marine ecosystems, particularly as environmental changes and human activities increasingly impact food availability. Sustained research and conservation efforts will be crucial to maintaining the health of pilot whale populations and the ecosystems they inhabit
