SOURCE: Scientific American

DATE: July 9, 2020

SNIP: The danger to whales and other large marine mammals from oceangoing vessels’ propellers and bows has long been recognized. And efforts are in place to track and curb such ship strikes. But a new study published in Frontiers in Marine Science finds that ships are also hitting large numbers of smaller marine animals—which are suffering severe injuries or dying at higher rates than previously thought.

The researchers sifted through necropsy results, eyewitness reports, and other anecdotal data from around the world and found that ships and smaller craft hit 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 ridley sea turtle and the endangered Hector’s dolphin. Younger animals are particularly at risk, because they are more playful and less experienced and might be left alone while a parent forages for food. Species that spend a lot of time sleeping at the surface, such as otters, also face a higher level of hazard. “When we started looking into this, I was quite surprised that all these other species are also being affected,” says Stephanie Plön, senior author of the study and now a cetacean biologist at the Bayworld Center for Research and Education, a South African nonprofit.

Strikes involving smaller species may be missed because crews are less likely to notice them than they would a collision with a massive whale, says Plön, who was at Nelson Mandela University in South Africa when she conducted the research. The bodies of such creatures might also sink or be eaten more quickly than those of larger marine mammals, which sometimes wash onshore, where they can undergo a necropsy. And previous research has found that even strikes with larger animals still remain undercounted.

Frazer McGregor, a marine ecology doctoral student at Murdoch University in Australia and lead scientist at a research collaboration called Project Manta, was not involved with the new study but says it matches his own findings. A paper he published in PLOS ONE last year reported that many injuries to manta rays in Western Australia’s Ningaloo Coast World Heritage Area that had originally been attributed to predators were actually caused by strikes, many likely made by small recreational boats. This reassessment was prompted when one of the area’s large resident female mantas suffered obvious propeller injuries: evenly spaced cuts that were deep and slightly curved.