The impact of whale swims in Tonga

The impact of whale swims in Tonga

A couple of days ago an eagerly-awaited piece of research was published about the behavioural effects of whale swims on Humpback Whales in Tonga. It revealed two key findings. 


Average diving time and the proportion of time spent diving in the presence of swimming activities increased significantly for mother-calf pairs

What this means is cows and calves spend less time resting, which means calves spend less time suckling, when in the presence of swimmers. 

A study published in Nature in January in Australia puts this into context (see below). Calves spend a significant amount of time suckling and lactating females spend a lot of time resting. 

Not only can females lose up to a third of their body weight during their six months in the tropics, they are recuperating from giving birth while suckling new born calves that are growing rapidly. The cow’s milk helps the calf put on about 40kg of weight daily (about half the weight of a human adult). In order to survive, the two have to function as a single unit, which means the effect of disturbance is doubled. 

The figure (above) is adapted from Bejdar et al. (2019)
While it’s difficult to gather direct evidence of the relationship between calf weight-gain and its later survival, it’s common sense to presume calves that have less time to feed and weigh less when they leave their breeding grounds will, on average, do less well. 
What we learn from this study confirms what we already know, that cow-calf pairs are more prone to disturbance and will change their behaviour accordingly.
This is why we do not swim with cow-calf pairs in Tonga.  


Avoidance responses of whales towards tour vessels were observed for one third of vessel approaches, significantly affected by the boat approach type. 
Unsurprisingly, avoidance was least when boats approached in parallel than when they drew up in front of whales.
Even with parallel approaches, however, there is always some effect. 
The underwater noise of a boat and its presence can be expected to affect the behaviour of whales. However, it is rarely necessary to approach whales too closely, especially if the intention is to interact with them. Any attempt that makes the whales uncomfortable will result in a worse experience for everyone involved. 
The only way to effectively do this is if the whales choose to approach, which means they have to be in just the right mood and otherwise unoccupied. Whales that are chasing females, resting, singing or otherwise socialising, may not care to be interrupted. 

Consequences for whale swim operators

Of all the 'whales', Humpback Whales are the only species where it's reliably possible to swim in their company, on their terms. Even then, it takes a lot of time to do well.   
The only way to swim without having an impact on calves is in the absence of almost any disturbance. Watching from a distance, taking your time, letting the whales choose to swim (and not the people) results in more sustained and enjoyable encounters.  

Find out more about whale swims at:

The picture at the top is of a pair of whales that definitely wanted to be swim with. When whales become this curious, it's usually long after we've got swimmers out of the water. While this situation is 'ideal', it also needs to be managed carefully to ensure guest safety. It goes to show, the level of expertise needed to do this well requires an intimate knowledge of not only how to handle a boat but also how to read whale behaviour and manage guest expectations and safety.