The call of a whale has long been immersed in human cultures. It features in Hawaiian traditional songs such as “Gods of the Sea”, is the root of well-known maritime tales (think Moby Dick), and has graced David Attenborough documentaries.
However, as humpback whales migrate along populated coastlines, they’re likely to encounter noise of human origin that can harm their ability to communicate with one another.
An Australian study published in Royal Society Open Science examines how noise from vessels can affect humpback communication networks.
According to author Rebecca Dunlop, from the University of Queensland, vessel activity along Australia’s east coast (and likely other populated coastlines) is increasing due to the growth of tourism.
For humpback whales, interactions with vessels are becoming more of an issue.
Current Australian measures protecting whales from boats include caution zones (within 300 metres of the whale) and exclusion zones (within 100 metres). The assumption, writes Dunlop, is that staying more than 300 metres away “reduces the risk of disturbance to natural behaviours”.
The results of her study suggest otherwise.
There are several natural sources of underwater noise, such as from breaking surface waves during storms. Noise of human origin includes such things as vessel activity, oil and gas exploration or naval sonar.
Though the effects of human-made noise on humpback whale communication and social behaviour were likely to be short-term and localised, an increase in vessel activity due to tourism and coastal population growth may cause more sustained changes along whale migration paths.
Previous studies have found that the communication space of humpback whale “signallers” – the individuals emitting the sound – extends to approximately four kilometres. The distance these social signals extend from the signaller defines its communication space, and therefore communication network (the number of potential receivers).
In increased natural noise, signallers maintained this four kilometres space by strategies such as increasing their vocal level or switching from vocal sounds to surface-generated sounds.
However, in cases of increased vessel noise, there’s no evidence that the whales use either of these anti-masking strategies.
This implies that when vessels are nearby, the communication space of humpback signallers is significantly reduced and that whales near vessels are 50% less likely to communicate.
Dunlop maintains that the full impact of vessel noise on whales and their breeding interactions (if any) is not yet known.
What’s clear, she says, is that the harmful effects of vessels on whales aren’t limited to collisions and increased signal masking. The potential effects on vital behaviours, such as breeding interactions, should also be considered and investigated.