Every morning the birds sing in chorus. But if you were to stick your head below the waves, you might just be able to pick up on another sonorous sound, and we’re not talking about whales. It turns out that Atlantic cod are fairly vocal creatures that even seem to have regional accents.
Cod use their swim bladders to create a kind of grunting sound, to communicate with other cod. They do this to establish territory, raise alarm, and attract mates, with the males having to vocalize in order to get the females to release her eggs before he can fertilize them. But they don't all "speak" the same.
“Recordings of American cod are very different to those from their European cousins, so there is a precedent,” explains the University of Exeter’s Professor Steve Simpson, who will be presenting his research at the Into The Blue science showcase in the UK. “This species is highly vocal with traditional breeding grounds established over hundreds or even thousands of years, so the potential for regionalism is there.”
Above, American cod as recorded by the researchers
But with climate change, the regional difference between fish accents could start posing a problem. Cod typically live in colder waters, and as the oceans warm their populations have begun to shift north, following the colder water. This means that populations that have previously been reproductively isolated could be pushed together, and so the researchers suggest that they may find it difficult to understand each other as they establish territories, warn for danger, and attract mates.
The fish may also be at risk of being simply drowned out, too. With all the extra noise from shipping and industrial activities going on in the oceans, the cod may be finding it difficult being heard above the din.
It’s already well established that this can impact whales and dolphins with serious consequences, but it seems that it may also be having effects on the fishes too, particularly as the fish need to be vocal in order to reproduce. If they can’t hear each other, it may impact their breeding.
And here's the European cod
“We may find that the ‘gossip’ essential to their society is being drowned out,” said Simpson. “If we value our fish stocks – or our Friday night fish supper – we need to understand this.”
While solving the issues surrounding the warming of the oceans is a little more complicated and going to take a fairly long time, there are things that can be done to limit the noise pollution, argue the researchers.
Most research boats are now being built to specifically have quieter engines, and this could be extended to other commercial vessels. Another possibility would be to create no-go zones for boats over important breeding grounds when the fish are doing the dirty below the waves.