Sperm whales use echolocation clicks made up of multiple pulses to navigate, find food and communicate. The time it takes for each pulse to travel from the air sac where it is produced, to the front of the head and back is known as the inter-pulse interval (IPI). This contains information on the length of a sperm whale’s head (i.e. the longer the interval, the longer the head) which can be used to calculate their total body length.
University of Otago researchers studying sperm whales in Kaikoura used acoustic data, specifically the IPI’s to determine the size structure of the population. They found that during recent summers, there has been an increase in the average length of the whales visiting the area but no trend for those in Winter. This increase in summer is likely due to individual whales returning to the area and who are growing in size year on year. This is supported by the already known knowledge that the number of smaller, previously unknown individuals joining the population is decreasing.
This indicates that the whales that are present in Kaikoura summers are an aging population which may have future impacts on the wider ecosystem.