Canada: Low plankton levels boost call for lowering noise levels

Plankton – small animals, algae, and microorganisms floating in the ocean – are the basis of the marine food web and thus of marine wildlife from corals to large whales. Hence, we should be more than alarmed when there’s evidence that human activities cause a dramatic drop in the number of plankton. And that’s exactly what seems to be caused by intensive noise emitted by seismic testing on behalf of the oil and gas industry.

As iPolitics recently reported, data collected by scientists with the Canadian federal Department of Fisheries and Oceans (DFO) have revealed a steady decline over the last five years in phytoplankton and zooplankton in the waters off Newfoundland and Labrador.

“We’re looking at values that are about 50 per cent of what we saw five years ago. That’s a substantial decline. And it’s not only a decline in the overall biomass; we’ve also seen a shift in the composition of the plankton,” iPolitics cites Pierre Pepin, a senior researcher with the department in St. John’s, N.L. There’s been a shift toward smaller species of the plankton.

At the Federation of Independent Sea Harvesters of Newfoundland and Labrador (FISH-NL), President Ryan Cleary says his members don’t need another study to confirm what they experience every day on the water. “Whenever a seismic boat goes past and we drop our gear, the fish aren’t there,” he told iPolitics. Another fisherman compared seismic testing to a snowplough, clearing out everything in its wake.

Seismic surveys produce the loudest human-made sounds in the ocean aside from explosions. The process involves towing air guns behind ships and shooting loud blasts of compressed air through the water and into the seabed to find oil and gas deposits that may be buried there. The guns release at high pressure and can go off every 10 seconds around the clock for months at a time.

In the waters around Newfoundland and Labrador, seismic testing has increased dramatically in recent years, and the same is true for many other regions in the world, from the Mediterranean to Australia. There, a study published in 2017 in the journal Nature found that seismic testing can destroy plankton populations.

The research by the University of Tasmania and Curtin University found that within the 1.2-kilometre range sampled, air-gun signals that are commonly used in marine petroleum exploration can cause a two- to three-fold increase in mortality of adult and larval zooplankton.

In 2018, Lindy Weilgart of Dalhousie University, who has been studying underwater noise for 25 years, produced an extensive report commissioned by OceanCare, a marine conservation organisation working in international fora to reduce ocean noise. The study reviewed 115 primary studies on human-produced underwater noise sources affecting 66 species of fish, 40 species of marine mammals and 36 species of invertebrates. It showed zooplankton suffer high mortality in the presence of noise.

Weilgart told iPolitics that she used to think plankton weren’t affected by sound. “I would not have put plankton in one of the categories that I’d initially have been worried about, but here we are. Plankton supports all life in the ocean. That’s why (what’s happening) is particularly worrisome.”

OceanCare’s report also includes a number of management and mitigation recommendations, from technological alternatives for seismic testing, such as Marine Vibroseis, to protecting acoustic refuges. However, the political will to implement these available remedies is still lacking.

Noise adds to the many stressors humans put on the ocean, from pollution to absorbing most of the carbon dioxide we’re putting in the atmosphere. Evidence that intensive noise may disrupt the basis of the marine food web should make us very careful. And of course there are many other reasons, from oil spills to climate change, that should make us turn away from further exploring oil and gas deposits in the seabed.