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New research finds that large numbers of small marine animals are seriously injured or killed at higher rates than previously thought.
The danger to whales and other large marine mammals from the propellers and bows of ocean vessels has long been recognized. And efforts are underway to track and stop such ship attacks. But a new study published inFrontiers in Marine Science finds that ships are also hitting large numbers of smaller marine animals, seriously injured or killed at higher rates than previously thought.
Researchers analyzed necropsy results, eyewitness reports and other anecdotal data from around the world and found that boats and smaller vessels struck at least 75 species, including dolphins, sharks, sea otters, seals, penguins. and sea turtles. Among them are vulnerable species such as the critically endangered Kemp's sea turtle and the endangered Hector's dolphin.
Younger animals are at particular risk because they are more playful and less experienced and may be left alone while a parent forages 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 researching this, I was quite surprised that all these other species are affected as well," says Stephanie Plön.
Attacks involving smaller species can be overlooked because crews are less likely to notice them than they would in a collision with a massive whale, says Plön, who was at Nelson Mandela University in South Africa when he conducted the research. .
The bodies of such creatures can also sink or eat more quickly than those of larger marine mammals, which are sometimes washed ashore, where they can be necropsied. And previous research has found that even attacks with larger animals remain uncounted.
Frazer McGregor, a doctoral student in marine ecology at Murdoch University in Australia and the lead scientist for a research collaboration called Project Manta, was not involved in the new study, but says it agrees with his own findings.
An article you published onPLOS ONE reported last year that many manta ray injuries in the Ningaloo Coast World Heritage Area of Western Australia, which were originally attributed to predators, were actually caused by small pleasure boats.
This reassessment was decided upon when one of the area's large resident blankets sustained obvious helix injuries: evenly spaced cuts that were deep and slightly curved.
Researchers initially thought that the scars would remain for life. But the following year they noticed that the animal had healed. This result prompted another look at the images in their database and a new analysis of scarring and healing of the blankets. "We realized that it is much higher than we thought, so that's a concern," says McGregor. "It means that they are likely to hit a lot more animals than we are recording, because they heal quickly and the next time we see them, they are cured."
Even though the blankets seem to heal well in a short time, he says, such injuries can have long-term negative effects. If one of these animals survives a hit but loses its tail or parts of its wings or reproductive claws, its competitiveness and continued survival will be at risk.
Plön's study also points out that a beaten animal needs to use energy for “body maintenance,” and that the energy would otherwise have been used to search for food, grow and reproduce. McGregor says that sightings of the area's stingray population have declined somewhat, possibly at least in part due to the death of animals after being hit by boats.
Other research has illuminated the particular ways that ship attacks affect a variety of species, including some of those mentioned in Plön's latest work. A 2019 study in theJournal of Wildlife Management found that from the mid-1980s to mid-2010, the number of loggerhead turtles struck by boats off the coast of Florida increased with the number of boats registered in the state.
And in the Arctic, Caspian seals were more likely to be struck at night, when ships broke through ice in their breeding grounds, according to a 2017 study inBiological Conservation, the seals did not move away from the boats until they were very close, possibly because the bright lights from the boats may have stunned the animals.
An easy way to reduce strikes is to simply slow down. There is a direct relationship between injuries and vessel speed, says Simone Panigada, co-coordinator of vessel attack for the International Whaling Commission and president of the Tethys Research Institute, a non-profit marine conservation organization. For example, boat operators voluntarily slowed down in New Zealand's Hauraki Gulf, where Bryde's whales live. "The attack rate of the ships decreased by almost 100 percent," says Panigada. He adds that whale detection apps are also a useful tool for alerting 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 will likely mean an increase in the traffic of large vessels and therefore, Marine animal injuries and deaths related to the vessel, Plön says. And he notes that that effect will only add to the myriad pressures on marine animals, including warming ocean waters, ocean pollution and noise, leading to "more and more of these cumulative impacts."
By Danielle Beurteaux. Article in English
