A STUDY by a European research team, including scientists at the University of St Andrews, has shown man-made noise pollution is sensed by whales similarly to how they sense predators.
It explains why some species are particularly sensitive to man-made underwater disturbances.
The report was led by a team of behavioural ecology experts including professor Patrick Miller and Dr Saana Isojuunno from the university’s Sea Mammal Research Unit (SMRU).
The report says cetaceans – whales, dolphins and porpoises – have to face choosing “life over dinner.”
Their responses to sounds from man-made noise such as military sonar systems are shaped by how they evolved to respond to natural predators like killer whales.
Underwater noise disturbances created by humans are also causing them to stop foraging and therefore become more vulnerable by impacting their energy budgets.
The findings were part of a project involving European colleagues including oceanographer Dr Frans-Peter Lam of acoustics and sonar at the TNO in the Netherlands.
Dr Petter Kvadsheim, principal scientist in sensor and surveillance systems at the Norwegian Defence Research Establishment contributed along with Charlotte Cure of the Joint Research Unit in Environment Acoustics.
SMRU PhD student Eilidh Siegal as part of the S3 (sea mammals, sonar and safety) team was also involved in the study.
The S3 research team found that navy sonar caused cessation of foraging in all four species of whale they studied – beaked northern bottlenose, humpback, sperm and long-finned pilot whales.
All four whale species rely on acoustic signals to assess predation risk as well as to find food and themselves.
Professor Miller, co-lead author of the report with Dr Isojunno said: “The fact that whales and dolphins can be negatively affected by sonar sounds came to the attention of the public due to high profile stranding events in which large numbers of whales stranded in association with military sonar activities.
“In the early-to-mid 2000s, several different research groups, including our 3S group which authored this most recent work, established novel procedures to directly study how the behaviour of free-ranging whales is affected by exposure to sonar sounds.”
Since 2006 the team has documented the behavioural responses of six species of cetaceans off the coast of Norway while other species have been studied by groups working primarily in the USA.
He explained that data for the latest study showed that when marine mammals tagged with temporary transmitters were played naval sonar or killer whale sounds the amount of time they spent foraging decreased.
Data varied between species with beaked northern bottlenose stopping foraging completely while sperm whales showed just a 50% reduction in foraging time.
Professor Miller added: “As human activities impact virtually every animal habitat on the planet, identifying species at risk from disturbance is a priority.
“Measuring reduction in intense feeding activities during playbacks of killer whale sounds showed a strong correlation across species close to a 1:1 line.
“In our study, matched responses of naval sonar and predatory killer whale sound playbacks indicate that whales who are both predators and prey but rely on hearing to both find food and detect dangers have not adjusted their threat response by learning to tell the difference between noise that does not represent a predation risk from that which does.
“Effectively they are having to choose life over dinner when they hear a potential threat in the sea.
“This is a particular concern for Arctic cetaceans, with both killer whales and humans increasingly able to access Arctic waters due to melting sea ice.
“Several Arctic marine mammals use crypsis and flight to avoid falling victim to killer whales and similar responses have been reported to ice-breaker noise and airguns used in oil and gas exploration.
“Our findings show that these Arctic marine mammals face a looming ‘double whammy’ impact of increased number of real predators as well as perceived threats from increasing human noise under the sea.”
The full paper can be found at https://doi.org/10.1073/pnas.2114932119
