Is COVID-19 Locking Down Underwater Sound?
COVID-19 may be silencing our streets, but it’s also quieting our seas. Around the Port of Vancouver, shipping routes are emptier than usual, cargo-carriers docked as traders weather the economic shock. For us, the virus is a curse, but for marine animals, it could be a blessing in an unexpected way. As this study shows, both inshore and offshore, recording devices show that a hush has fallen even underwater.
The data comes from Ocean Networks Canada with its two ocean observatories. They gather all sorts of information about the changing seas. NEPTUNE, the observatory in the northeast Pacific Ocean, detects noise from the trade routes leading to the Vancouver and Seattle ports. Further inshore, VENUS records sound from the Salish Sea, with nodes very close to major ferry routes. Each observatory has two recording devices, called nodes, mounted on the seabed. They capture the underwater soundscape, which is made up of sounds at different frequencies.
The 100 Hz range is home to most of the humming and thrumming of passing ships, but not the usual ocean ambience. Researchers analyzed the intensities of different frequencies within this range and produced summary figures for weekly noise levels. They focused on 2020’s first three months, comparing NEPTUNE’s data with previous years’, and VENUS’ data with previous weeks.’
One of NEPTUNE’s recording devices detected a ~1.5-decibel drop in shipping-related noise levels compared to averages over the past three years. The other found no significant difference, possibly because it was less sensitive to shipping noise. Replacement issues kept researchers from comparing VENUS’ audio with previous years. Instead, they showed that noise levels decreased week by week since the beginning of January through to the end of March. To be precise, the node directly beneath a well-travelled passage reported, on average, a 0.59-decibel quietening every week. The other, further away, reported a 0.25-decibel drop per week.
Other forms of data support these findings. Statistics Canada compared the first two months of 2020 with 2019. They found a 16% decrease in trade activity across the country. Unsurprisingly, the amount of cargo shipped in and out of the Port of Vancouver decreased by 13% compared to last year. Comparing the first three months of both years, the number of shipping vessels in the area also reduced by over 20%.
In other words, fewer boats and lighter loads are chugging about on Vancouver’s seas. But what kind of effect does this have on marine animals? Human ears wouldn’t register a one-decibel change in noise levels, but would we say the same for underwater ears?
First of all, the changes were detected all the way from the seabed. VENUS’ two nodes were 200 and 150 meters below sea level. NEPTUNE’s were one and two kilometers deep. That’s a long way from the surface. Sea creatures, on the other hand, dwell at all depths of the water column. We can be sure that shipping noises are more disruptive where they are.
What’s more, many marine animals rely on hearing to navigate, so their sense is keener than ours. Among these, orcas and dolphins, seals and countless fishes make their home in the northeast Pacific and the Salish Sea. Background noise can confuse their feeding and breeding habits, stifle their learning ability, and make avoiding predators more difficult.
So, a little hush is not inconsequential after all. Just imagine the rest of the world’s oceans. Imagine all of those watery residents. A little peace and quiet for a lot of fins and flippers – that’s a great deal of respite.