The research, published recently in the journal Proceedings of the Royal Society B, assessed how underwater visibility affects the ability of seabirds to forage for fish and other prey – making it one of the first studies to examine the impact of ocean clarity on the diving abilities of birds.
For the study, scientists, including those from the University College Cork (UCC), attached tiny trackers to the feathers of the seabird Manx shearwater (Puffinus puffinus) in Little Saltee, a small island off the coast of Ireland.
They analysed the diving patterns of the black and white Manx shearwater birds in relation to local environmental conditions like cloud cover and water clarity.
Over 5,000 different dives were recorded and data on a wide range of factors like weather patterns and ocean conditions like water turbidity, cloud cover and solar angle with the help of publicly available databases was collected.
The study found the birds dove deeper when sunlight could penetrate further underwater, suggesting visibility is key to their ability to dive for food.
Less than one per cent of the bird’s dives occurred when the sun was over 6 degrees below the horizon.
Based on this observation, scientists said the dives were preceded by visual detection of either prey or indicators of prey, such as other predators by the birds.
Researchers also found cloud cover had a negative effect on the depth to which the birds dove.
“Our findings support the idea that the birds needed sufficient sunlight to be able to forage at depth,” Jamie Darby, a marine ecologist at UCC, and lead author of the study, said in a statement.
However, scientists pointed out that global warming was causing the oceans to become cloudier.
“Large marine areas have become more turbid in recent decades, driven by increased wave action and seabed shear stress associated with climate change,” they wrote in the study.
Researchers warned the climate crisis is altering the location, timing and intensity of plankton blooms in oceans that can severely limit visibility “for months at a time over vast areas”.
Such plankton blooms, with the potential to turn the waters turbid, “have resulted in mass die-offs due to starvation” when they occur in important seabird habitats, scientists said.
“The chemical and physical properties of the planet’s oceans are changing at an unnatural rate, bringing about challenges for marine life. One consequence of climate change is that large areas of our oceans are becoming cloudier,” Dr Darby said.
While the research examined only one particular seabird, scientists said the results can be extended to other animals.
“Many visually-dependent predators could find themselves struggling to find food as human activities continue to make the oceans murkier,” Dr Darby added.
“Our data indicate that climate change could negatively impact seabird populations by making prey more difficult to detect, compounded by the widely reported effects of reduced prey populations,” scientists concluded in the study.