Researchers studying seabird populations in the Sister Islands have discovered evidence of the devastating impact of discarded plastic in the ocean.
Scientists working on two separate studies have taken gruesome pictures of rare seabirds tangled in fishing line and snagged in the branches of trees around Little Cayman.
The research team, which is currently tagging and tracking frigate birds to find out more about their behaviour and range in the Caribbean, hope their work will help inform international conservation management plans to protect the species.
Abandoned plastics, particularly monofilament fishing line, have long posed a threat to sea creatures. Just last week, a juvenile green sea turtle was found dead, entangled in fishing line off Duck Pond Cay in North Sound. But the findings of the seabird study team show the extent to which the issue is also impacting life in the skies.
Jane Haakonsson, a research officer with the Cayman Islands Department of Environment, said, “We have seen an alarming number of birds hanging in the trees in the Booby Pond area of Little Cayman.”
She said the birds ingested fishing hooks and lines while foraging at sea. When they get back to the roost, they become tangled in the branches and cannot escape.
Haakonsson said the problem illustrated the importance of international cooperation to protect seabirds.
Frigates may roost in the Cayman Islands, but the satellite tags from a previous Department of Environment study show that they roam far and wide, foraging in international waters. One bird tracked by the study team was recorded as far away as New Orleans before returning to Little Cayman.
Haakonsson said discarded fishing line was a major problem in the waters around Cayman and within the bird’s foraging radius.
“We don’t have commercial fisheries in the Cayman Islands,” she said, “but the waters they are fishing in do.
“With species that travel further and wider, we are looking at international collaboration on protection.”
The latest study, led by University of Liverpool researcher Rhiannon Austin, looks specifically at frigate birds.
The Department of Environment is supporting the UK Darwin Initiative-funded project, which will also study frigate colonies in Anguilla and the British Virgin Islands.
Researchers have tagged 26 frigate birds in Little Cayman so far. They aim to examine the behaviour of the species in the three main life cycles – fledglings, juveniles and nesting adults.
While nesting pairs are known to roost permanently in Little Cayman, the study team wants to find out if juveniles move between colonies as they search for a mate.
“We don’t know much about the life stage prior to becoming nesting pairs,” Haakonsson said.
“It would make perfect sense if there was movement between the colonies from a genetics perspective, but it would have implications for management.
“While we have Booby Pond protected, that only goes so far. If the genetic material is coming from another colony, we have to get that protected too.”
An earlier study, also a collaboration with the University of Liverpool, yielded interesting results about all three types of seabirds on the Sister Islands.
The researchers even managed to attach a camera to a frigate bird to get a literal ‘bird’s-eye view’ of its foraging behaviour. Shaky footage shows a bird soaring over Little Cayman and fighting off rivals for its catch.
Haakonsson says this footage is one example of why the birds are known as the “pirates of the sky”. She said they had frequently been observed stealing fish from each other or from the boobies, which run a nightly gauntlet as they return to the roost with their fish.
The earlier study also provided useful information about the population sizes and ranges of brown boobies, red-footed boobies and frigates.
Haakonsson said frigates were sometimes gone from the nest for weeks at a time, flying hundreds of miles.
“None of this was known until we started tagging them,” she added.
It is hoped that the projects’ findings will help inform international cooperation over species protection.
Haakonsson said the new study would also enable scientists to pinpoint key fishing grounds for the frigate birds and work with regional partners to protect them.
One homegrown problem impacting Cayman’s seabirds is not going away. She said the birds continue to be preyed on by feral cats.
The department had hoped to cull the cats, but that process was paused amid a legal challenge and is still delayed pending the appointment of an Animal Welfare Committee.