Seabird Colony Depletes Nearby Fish Stocks

Home Conservation Seabird Colony Depletes Nearby Fish Stocks
Seabird Colony Depletes Nearby Fish Stocks

A vast seabird colony on Ascension Island creates a “halo” in which fewer fish live due to their predation, new research shows.

Ascension, a UK Overseas Territory, is home to tens of thousands of seabirds—of various species—whose prey incudes flying .

The new study, by the University of Exeter and the Ascension Island Government, finds reduced flying fish numbers up to 150km (more than 90 miles) from the island—which could only be explained by the foraging of seabirds.

The findings—which provide rare evidence for a long-standing theory first proposed at Ascension—show how food-limited seabird populations naturally are, and why they are often so sensitive to competition with human fishers.

“This study tells us a lot about large colonies of animals and how their numbers are limited,” said Dr. Sam Weber, of the Centre for Ecology and Conservation on Exeter’s Penryn Campus in Cornwall.

“These birds are concentrated at Ascension Island during the , and the intensity of their foraging is naturally highest near the island.

“As they use up the most accessible prey located near to the island, they have to travel increasingly long distances to feed, causing the ‘halo’ to expand outwards.

“Once individuals can’t find enough food to break even with the energy they expend finding it, the colony stops growing.

“Human impacts such as fisheries can interfere with this natural balance and have on populations of marine top predators like seabirds, even if they don’t directly harm the birds.