The danger to whales and other large marine mammals posed by the propellers and bows of ocean-going vessels has long been recognized. And efforts are in place to track and curb these collisions with ships. But a new study published in Frontiers in marine sciences finds that ships also strike a large number of smaller marine animals, which suffer serious injuries or die at higher rates than previously thought.
Researchers sifted through autopsy results, eyewitness reports and other anecdotal data from around the world and found that ships and small craft affected at least 75 species, including dolphins, sharks , sea otters, seals, penguins and sea turtles. Among them are vulnerable species such as the critically endangered Ridley de Kemp sea turtle and the endangered Hector’s dolphin. Young animals are particularly at risk because they are more playful and less experienced and can be left alone while a parent searches for food. Species that spend a lot of time sleeping on the surface, such as otters, also face a higher level of danger. “When we started to study this, I was quite surprised that all of these other species were affected as well,” said Stephanie Plön, lead author of the study and now cetacean biologist at the Bayworld Center for Research and Education, a South African non-profit organization. .
Collisions involving smaller species can be missed because crews are less likely to notice them than a collision with a huge whale, says Plön, who was at Nelson Mandela University in South Africa when she conducted the research. . The bodies of these creatures could also sink or be eaten faster than those of larger marine mammals, which sometimes wash on the coast, where they can undergo an autopsy. And previous research has shown that even strikes with larger animals remain underestimated.
Frazer McGregor, a doctoral student in marine ecology at Murdoch University in Australia and lead scientist in a research collaboration called Project Manta, was not involved in the new study, but says it matches her own findings. An article he published in PLOS ONE Over the past year, many of the wounds inflicted on manta rays in Western Australia’s Ningaloo Coast World Heritage Area, which were originally attributed to predators, were in fact caused by strikes, many of which were likely caused by small pleasure craft. This reassessment was triggered when one of the region’s resident large female mantas suffered obvious propeller injuries: evenly spaced, deep, and slightly curved cuts.
The researchers initially thought that the scars would stay for life. But the following year, they noticed that the animal was healed. This result prompted another look at the images in their database and a reanalysis of manta scars and healing. “We found out it was way higher than we thought it was, so that’s a concern,” McGregor said. “This means a lot more animals are probably affected than what we are recording because they heal quickly, and the next time we see them they heal.”
Even though mantas seem to heal well in a short period of time, he says, such injuries can have long-term negative effects. If one of these animals survives a stroke but loses its tail or parts of its breeding wings or claws, its competitiveness and survival will be threatened. Plön’s study also notes that a stricken animal needs to use energy for “body maintenance” – and that this energy would otherwise have been used for foraging, growth, and reproduction. McGregor says sightings of the area’s manta ray population have declined a bit, perhaps, at least in part, due to animal deaths after being struck by boats.
Other research has shed light on the particular ways in which collisions with ships affect a range of species, including some of those mentioned in Plön’s later work. A 2019 study in the Wildlife Management Journal found that from the mid-1980s to the mid-2010s, the number of loggerhead turtles impacted by boats off the coast of Florida increased with the number of vessels registered in the state. And in the Arctic, Caspian seals were more likely to be affected at night, when ships broke ice in their breeding grounds, a 2017 study in Biological conservation find. The seals only moved away from the ships when they were very close, possibly because the bright lights from the ships might have stunned the animals.
An easy way to reduce strikes is to simply slow down. There is a direct relationship between injuries and boat speed, says Simone Panigada, ship strike coordinator for the International Whaling Commission and president of the nonprofit Tethys Research Institute for Marine Conservation. For example, ship operators have voluntarily reduced their speed in New Zealand’s Hauraki Gulf, home to Bryde’s whales. “The strike rate of ships has dropped by almost 100%,” says Panigada. He adds that whale finder apps are also a useful tool to alert captains to slow down if animals are nearby or to avoid areas where they congregate.
For now, however, in the absence of clear official policies such as speed limits, the increasing development of ports, shipping, and offshore oil and gas development is likely to lead to an increase in large vessel traffic and , therefore, injuries caused by marine animals and marine animals. death, says Plön. And this effect, she notes, will only add to the myriad of pressures on marine animals – including warming ocean waters, pollution and ocean noise – leading to “more and more of these. cumulative impacts “.