It’s a sight divers might hope never to see, but for the first time researchers have recorded images and data of a shark being struck by a boat.
The incident occurred only hours after the 7m female basking shark had been tagged by the scientific team off Ireland, resulting in the attached camera and sensors capturing the full effects of the impact.
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Earlier this year, the government established Ireland’s first National Marine Park on its Atlantic coast, protecting 70,000 acres of land and sea around Co Kerry, where basking sharks gather seasonally to feed and potentially mate.
The researchers were on a field-trip to learn more about how the sharks’ foraging behaviour reflected environmental factors. They had attached the activity-measurement device while the shark was feeding at the surface, and had followed in their boat at a safe distance for several hours before leaving the area.
On retrieving the released tag the next day they discovered that the shark had continued with its normal surface-feeding behaviour, carrying out occasional dives, until it suddenly made a rapid evasive movement. A boat’s keel could be seen cutting across its back, just behind its dorsal fin.
The shark tumbled, its tail immediately beating faster as it headed straight down to the seabed. Video showed paint marks and a red abrasion on its skin but no apparent bleeding or open wound.
For the scientists this was a unique opportunity to learn more about boat-strike, a matter of increasing global concern. The incident occurred in April and the team’s study has just been published.
First direct observation
“This is the first ever direct observation of a ship strike on any marine megafauna, that we’re aware of,” said Taylor Chapple, a shark researcher at Oregon State University (OSU)’s Hatfield Marine Science Centre and the study’s lead author. RScientists from Stanford University, Trinity College Dublin and other institutions were also involved in the study.
“The shark was struck while feeding on the surface of the water and it immediately swam to the seafloor into deeper, offshore waters, a stark contrast to its behaviour prior to the strike. Our findings demonstrate the risk and impact of vessel strikes and the need for measures to reduce this risk.”
The researchers cannot say whether the basking shark survived the strike, because the tag was timed to release itself for retrieval seven hours after it occurred. All they know is that during this time the animal did not resume feeding or other normal behaviour. Even non-lethal injuries can have short- and long-term consequences, they point out.
Basking sharks are IUCN Red-Listed as Endangered globally but continue to aggregate in large numbers off Ireland, where they were protected under the country’s Wildlife Act in 2022. While susceptible to strikes while feeding at the surface, unlike whales they tend to sink after a strike occurs, making it more difficult to gauge their mortality rates.
“This research raises additional questions about whether and how often the sharks are actually occupying such habitats when they are not clearly visible at the surface,” commented co-author Alexandra McInturf, a research associate in Taylor Chapple’s Big Fish Lab at OSU and co-co-ordinator of the Irish Basking Shark Group.
“Given that Ireland is one of the only locations globally where basking sharks are still observed persistently, addressing such questions will be critical to informing not only our ecological understanding of the basking shark, but also the conservation of this globally endangered species,” said McInturf.
The study has now been published in Frontiers in Marine Science.
Also on Divernet: Basking sharks meet to eat – and show off, Robot sheds light on basking sharks, Wanted: Divers’ oceanic & basking shark sightings, Coast-to-coast basking shark
