A Colony of Seabird Creates "Halo" to Mark Areas with Fewer Fish Population

According to a new study, a large seabird population on Ascension Island creates a "halo" in areas which fewer fish thrive. Tens of thousands of seabirds of various kinds live on Ascension, a UK Overseas Territory, and their food includes flying fish.

The University of Exeter and the Ascension Island Government have discovered lower flying fish populations up to 150 kilometers (about 90 miles) away from the island, which can only be explained by seabird feeding.

Initial Idea

The findings, which give rare confirmation for a long-standing idea initially suggested at Ascension, demonstrate how food-limited seabird populations are in the wild and why they are often vulnerable to human fishing.

"This study reveals a lot about big animal colonies and how their numbers are constrained," said Dr. Sam Weber of Exeter's Penryn Campus in Cornwall.

Halo

During the mating season, these birds congregate on Ascension Island, and the intensity of their foraging is naturally strongest near the island.

As they consume the most readily available prey close to the island, they must travel long distances to eat, causing the 'halo' to extend outwards.

The colony stops expanding when individuals can't locate enough food to break even on the energy they waste in obtaining it.

Human Influences

Human influences such as fisheries can disrupt this natural equilibrium and have severe consequences for populations of top marine predators such as seabirds, even if the birds are not directly harmed.

"The size of the footprint we discovered was really striking.

It demonstrates that certain predators rely on food populations across a vast region. Therefore Marine Protected Areas may need to be quite large.

The study's pattern of prey depletion is known as "Ashmole's halo," after British naturalist Philip Ashmole, who originally postulated it following a visit to Ascension Island some 60 years ago.

The researchers counted flying fish, followed the foraging journeys of seabirds, and studied their regurgitated food for the study.

Frigatebirds, masked boobies, and brown boobies are among the breeding seabird species on Ascension that feed on flying fish.

Seabirds

Seabirds (sometimes referred to as marine birds) are birds adapted to live in the sea. While seabirds have a wide range of lifestyles, behaviors, and physiology, they often show dramatic convergent evolution due to similar environmental challenges and food niches. The earliest seabirds appeared during the Cretaceous, while contemporary seabird groups emerged during the Paleogene.

Diet and Physiology

Seabirds, on average, live longer, reproduce later, and have fewer young than other birds, but they devote a lot of time to their offspring. Most species lay their eggs in colonies that range from a few dozen to millions of birds. Many species are known for their extensive yearly migrations, including crossing the equator or even circumnavigating the globe. They eat both above and below the water's surface, and they even eat each other. Seabirds can be highly pelagic, coastal, or spend part of the year totally away from the water.

Living with Humans

These marine birds and humans have a long history together: they have fed hunters, guided fisherman to fishing grounds, and guided sailors to shore. Unfortunately, many species are presently endangered due to human actions, such as oil spills, getting caught in nets, climate change, and extreme weather. The creation of animal refuges and changes to fishing practices are examples of conservation initiatives.

Also Read: Jays Might Be Responsible for Planting Half the Tree Population in England's Woodlands

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Tags Seabird, marine life, Marine Ecosystems