Tiger sharks are known for their ferocity. The huge animals, which can grow to more than 16 feet, are ruthless predators and fear absolutely nothing – recent research has found that while other shark species flee coastal waters during strong storms, tiger sharks ‘don’t even flinch’ .
But recently, they have a new role that may help boost their reputation: marine scientists.
In an attempt to measure the extent of seagrass meadows in the Bahamas, researchers attached cameras and trackers to the dorsal fins of tiger sharks to give them access to hours of footage from the ocean floor.
The data they collected revealed what researchers say is the largest known seagrass ecosystem in the world, spanning up to 92,000 sq km (35,000 sq mi) of Caribbean seafloor. This discovery expands the total known global seagrass cover by more than 40%, according to the study published in Nature Communications on November 1.
“This discovery shows how far we are from exploring the oceans not only in the deep, but even in the shallows,” said report co-author Prof. Carlos Duarte of Saudi Arabia’s King Abdullah University of Science and Technology.
Seagrass meadows have long been understudied, with estimates of their total global area ranging from 160,000 sq km to 1.6 million sq km. Mapping is extremely challenging: meadows in deep or murky water cannot always be spotted by aircraft or satellites, while smaller ones can be sparse or intertwined with other marine plants, making them difficult to identify.
This means that seagrass meadows need to be ‘ground tested’ ie. confirmed by someone – or something – on the spot. But sending human divers to photograph vast swathes of the ocean floor is expensive, logistically challenging and very slow.
Tiger sharks are a different story. The highly mobile animals are able to reach considerable depths, have a large range and spend a lot of time in seagrass meadows. They are also unencumbered by ordinary human limitations such as the need for a boat, frequent surfacing, and dependence on calm ocean conditions.
Between 2016 and 2020, researchers attached camera packages equipped with satellite and radio tags to the dorsal fins of seven sharks. They caught the animals using round-hook drum ropes that hook into the animals’ jaws. It’s the “safest way to catch sharks” and causes no lasting damage, said Oliver Shipley, senior research fellow at Beneath the Waves, a marine science nonprofit and co-author of the report.
They reeled the animals in to secure the cameras in an operation Shipley likened to that of a “Nascar pit crew.” It took about 10 minutes to tie each bright orange camera using biodegradable cable ties and a time-release dissolvable swivel. After about six hours, the vortex corrodes in the seawater and the entire package floats to the surface where scientists can retrieve it.
Using marine animals like this opens a “window on the marine world” and can help answer questions about the climate crisis and biodiversity, said Richard Unsworth, associate professor at Swansea University and founder of the charity Project Seagrass. Unsworth, who was not involved in the study, said mapping seagrass is vital. “If we don’t know where it is, we can’t protect it,” he said.
Seagrasses are important nurseries and feeding grounds for many marine species, they support commercial fisheries and provide a buffer against coastal erosion. They are also a significant source of ‘blue carbon’, capturing and storing vast amounts of carbon on the seabed, making them a vital tool in mitigating the climate crisis.
Yet they are threatened by a variety of factors, including boating and shipping, coastal development and increasingly severe weather extremes. It is estimated that around 7% of seagrasses are lost globally each year. The UK has lost 90% of its seagrass meadows over the past few centuries.
The researchers hope their discovery will mean better protections for seagrass in the Bahamas — which is threatened by dredging for coastal development as well as pressure for aragonite mining — but also globally. Seagrass and other coastal ecosystems are “probably one of the best allies and assets we have in terms of natural attempts to mitigate the effects of climate change,” Shipley said.
He predicts that there will be many more projects partnering with marine animals to map ocean habitats. “They’re going to take us to new places we didn’t know existed.