Noisy boats over the Great Barrier Reef are cutting fish lives short

By Christa Lest.

Some young fish that live in coral reefs exposed to motorboat sounds are less likely to survive than fish on quieter reefs because of the noise pollution.

In reefs with motorboat noise, the parents fan their eggs less and seem more agitated.

Any kind of noise can cause a rise in stress. "I think that's what's going on here with the parenting behavior, and that's what I think."

She and her colleagues snorkelled every other day along the Great Barrier Reef in Australia to observe and photograph wild spiny chromis nests. In six experimental sites off the coast of Lizard Island, Australia, the team counted the surviving offspring every four days.

Three of the sites were limited boating zones, in which the scientists requested that motorboat drivers keep at least 100 metres away from reefs or, if necessary, get no closer than 20 metres away with no wake. The three other sites were busy-boating zones, in which the research team drove outboard engine aluminum motorboats within 10 to 30 metres of the reef. The team made these passes in the boats about 180 times a day, for about 90 minutes, to mimic a port harbour or popular tourist area.

She says that they found that breeding pairs in the limited boating sites were twice as likely to still have living offspring by the end of the three-month breeding season.

Read more: Coral reefs have conveyor belts of mucus running across their surface

The team captured spiny chromis adults and put them in a laboratory to study their parenting behavior. They played natural coral reef sound recordings through loud speakers for 12 hours a day for 13 fish pairs, and for another nine pairs, the recordings included 100 minutes of boating noise recorded from the reef.

Nedelec says boat noise didn't change the number of eggs the fish laid. The scientists noted that adults stopped fanning their eggs when they heard motorboat recordings, and they didn't fan more during quiet periods to make up for that. The fish became more active, swimming farther away from the nest, when they heard recordings of normal reef sounds.

21-day-old hatchlings were 4 per cent longer in limited boating conditions than in busy boating conditions. Nedelec says that smaller offspring might be more vulnerable to predator in the wild.

She says the change in parenting behavior affected hatchlings. Without boat noise, the chances of the young fish surviving to 3 weeks old almost doubled.

Nedelec says the findings suggest that fishermen, tourists, recreational boaters, cruise operators and even researchers could help reef-nesting fish populations recover from hurricanes and heat waves by slowing down their boats or avoiding reefs altogether.

Coral reefs go through intense climate shocks, and the populations that live there have to regenerate. It won't save coral reefs because it can't replace action on climate change. It could support their resilience.

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