Millions of sharks in the world's oceans may have fishing hooks stuck inside them with potentially serious health consequences, research indicates.

A team of scientists observed 55 individual tiger sharks for eight years off the coast of Tahiti in the South Pacific, finding that 38 percent of them had been hooked by fishing gear at least once during this period.

Worryingly, the team found that some of the these hooks stayed in place for years, and could potentially remain for the entire lifetime of the shark, according to a study published in the journal Fisheries Research.

"That can have profound consequences for those animals. It can injure or even perhaps kill them because they're unable to feed properly after these interactions," Carl Meyer, an author of the study from the University of Hawaii, said in a statement.

The team said it was common for sharks to have more than one hook embedded in their bodies at any one time. They even observed one shark with seven deeply-wedged hooks, and another with six.

The researchers say many tiger sharks get hooked by fisheries targeting tuna and swordfish using longlines.

"Longlines are lines that have multiple baited hooksfrom tens up to several thousandthat are set either on the seabed or midwater supported by surface floats," Meyer told Newsweek.

"They are typically left in place for several hours and then hauled in to recover the catch. High-seas longline fisheries primarily target high-value tunas and swordfish but also 'bycatch' other non-target species, including sharks.

"In most cases, the fishers do not want to catch sharksthe sharks are simply attracted to the same bait as target species, or to the hooked target species themselves.

"If hooked, sharks often break or bite the line, or are cut loose by fishers without them removing the hook. After these interactions, sharks may swim away with hooks embedded in their stomachs, throats, mouths or externally around the jawsor elsewhere on the bodyand may also be trailing line from those hooks."

For the latest study, Meyer and his team observed the 55 sharks at an ecotourism site off the northwest coast of Tahiti between 2011 and 2019.

"Gear retentionwhen marine animals escape from fishing gear with parts of the gear stuck on their bodieshas been recognized as a potential problem for some time but certain key questions have been very difficult to answer," Meyer said.

"Chief among these are: (1) How long do sharks retain embedded hooks and trailing line? And (2) What are the impacts of embedded hooks and trailing line on shark health?

"We realized that we could answer both of these questions using the tiger shark photo-identification data set where individual sharks, identified from unique characteristicsfor example, scars and natural markingswere photographed on multiple occasions over multiple years."

In the study, the team identified two main types of hooks: Those made from stainless steel and others made of corrodible material. All of the corrodible hooks fell off before a period of two-and-half years. Meanwhile, the stainless steel hooks could stay wedged in the shark for more than seven years.

"Internal hooks can cause internal bleeding," Meyer said. "External hooks can interfere with feeding. Trailing line can interfere with feeding, wrap around fins leading to necrosis (tissue death), and interfere with swimming."

Despite these potential risks, the researchers said that the tiger sharks in the study were relatively healthy even though they had embedded hooks and trailing line.

But Meyer puts this down to tiger sharks being particularly robust, describing them as the "Sherman tank" of the shark world.

They only observed one shark with an internal hook, opening up the possibility that many animals that suffer this fate end up perishing. "We predominantly observed individuals with externally embedded hooks, so the fate of tiger sharks with internal hooks is still unclear," he said.

"Individuals of other shark species with externally embedded hooks and trailing line have been observed in poor condition and struggling to feed normally, so this is a significant conservation concern especially given the millions of shark interactions with fishing gear that occur each year.

"This is a problem that likely affects millions of individual sharks across the world's oceans. Sharks are hooked in a broad variety of fisheries ranging from coastal recreational angling to commercial open-ocean longlining."

The problem is not limited to sharks. A wide variety of hook and line fisheries around the world also inadvertently hook non-target species including fishes, turtles, marine mammals, and birds.

In light of their findings, the team makes several recommendations to fisheries regarding the use of hooks.

"Fishers do not want to catch non-target species and increasingly understand the importance of reducing the impact of fishing on non-target species," Meyer said.

"Switching to the use of non-stainless hooks is not a panacea but will help to reduce impact by decreasing the time required for sharks and other animals to shed embedded hooks."

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Millions of Sharks Around the World May Have Fishing Hooks Stuck Inside Them, Scientists Suggest - Newsweek