57. How do whales navigate: part 2

When I last wrote on this subject (see blog #4) I focussed on the possible role of geomagnetism in helping humpback whales to navigate across oceans with remarkable precision.

Recently I came across an article (dating from 2020) that raises another possibility.

Perhaps migratory fish - which are known to be sensitive to infrasound (very low frequency sound below the threshold of human hearing) - make use of it to orient themselves?

The idea is that turbulence caused by ocean currents or seismic activity in the ocean floor (eg along mid-ocean ridges or around submarine volcanoes) gives rise to characteristic infrasound signals that are capable of travelling over great distances. Breaking waves along a coast are another infrasound source.

Any marine animal that can detect such sounds could in principle extract useful navigational information from them.

We know that many animals other than fish (including eg birds and elephants) can detect infrasound, so the possibility that whales may do so too seems plausible.

To the best of my knowledge, this idea remains speculative (it’s hard to experiment on whales!) but it’s not a big leap to imagine that whales (as well as migratory fish) may navigate with the help of infrasound.

Of course that wouldn’t conflict with the possibility that they may use geomagnetism. The two systems would complement each other well.

31.Joshua Slocum on the joys of celestial navigation

One of the things that bothers me about our ever-increasing reliance on technology is the way it distances us from the natural world.  Yes, yes – it makes life easier in all sorts of ways and it would make no sense to turn our backs on it, but all that convenience does come at a cost.

This is especially true of GPS.  Have you ever had had the slightly weird experience of allowing the in-car ‘satnav’ to lead you astray on a journey to a place you knew perfectly well how to find?  We’re so beguiled by its extraordinary accuracy and reliability that we daren’t challenge its authority.  GPS can be disabling – reducing us to a state of child-like dependence and making us behave like complete idiots.  In fact it actually weakens our ability to navigate naturally, as recent research has confirmed (see earlier post).

The Inuit peoples of Northern Canada worry that young people who have become reliant on GPS can’t safely find their way around in the Arctic wilderness and easily get lost – which is no joke up there.  Their elders, by contrast, just using natural cues like the sun and stars, landmarks of all kinds, the wind, the shapes of snow drifts, and the behaviour of the wildlife, can find their way in almost any weather.  Apparently they never get lost even if they sometimes have sit tight for a while when there’s a complete ‘white out’.

Over the last 20 years GPS has come to dominate marine navigation almost completely.  Integrated electronic navigation systems based on GPS are now installed even on small boats.  Basically they offer a ‘moving map’ display on which the vessel is represented by a little boat-shaped icon.  

Linked to the GPS – and maybe also to radar and other instruments – these ‘Electronic Chart Display and Information Systems’ (ECDIS) have taken all the hard work out of navigation.  With a click of a mouse you can find out how far you have to go to reach your destination, what the best course is, how long it’ll take to get there, how much current is against you and much else besides.  

It’s quite brilliant but it’s also totally infantilising.  You’re turned into a mere consumer of navigational information with no part at all in the complex business of generating it.  A glance at the display tells you exactly where you are – and  you don’t even have to raise your head to look at the world outside.

Maybe that’s fair enough if you’re a professional seaman who just needs to get safely from A to B by the fastest route, but there’s something a bit sad about recreational sailors relying on GPS and ECDIS – as they increasingly do.  After all, what’s the point of going sailing, if not to be experience the wonders of the natural world?   (I leave aside the point that exclusive reliance on electronic navigation aids is actually very risky - a subject I might come back to one of these days.)

The sea is the last great wilderness and there are few things more rewarding than to find your way across it with a sextant in your hand.  To fix your position in mid-ocean by taking sights of unimaginably distant stars is a truly sublime experience.  

As the first single-handed round-the-world yachtsman, Joshua Slocum (1844-1908), said after finding the Marquesa Islands just where he expected (using the old lunar distance method for finding longitude):

To cross the Pacific Ocean … brings you for many days close to nature, and you realize the vastness of the sea. Slowly but surely the mark of my little ship’s course on the track-chart reached out on the ocean and across it, while at her utmost speed she marked with her keel still slowly the sea that carried her. On the forty-third day from land,… the sky being beautifully clear and the moon being ‘in distance’ with the sun, I threw up my sextant for sights. I found from the result of three observations, … that her longitude by observation agreed within five miles of that by dead-reckoning.

28.Green turtles aren’t perfect navigators - but they don’t have to be

Charles Darwin was one of the first scientists to speculate about how sea turtles navigate on the open ocean. It’s a fascinating question and two whole chapters of Incredible Journeys are devoted to it.

One of the experts I interviewed was Paolo Luschi whom I visited at the University of Pisa. Paolo has spent many years doing experiments on turtles in the field, and he warned me to be sceptical of claims that these animals - remarkable though they are - are brilliant navigators.

A fascinating new piece of research reinforces his point.

Graeme Hays and his colleagues (including Paolo) tracked 33 green turtles migrating from their nesting beaches on the remote Indian Ocean island of Diego Garcia to their habitual feeding grounds dotted around the western part of that vast expanse of sea. The turtles travelled anything from a few tens of kilometers to more than 4,000.

Several interesting things emerge from the analysis of their data.

Firstly, the animals very seldom went directly to their destination - sometimes they massively overshot and they often strayed wildly off track. Nevertheless, they were still able eventually to locate their targets.

Secondly, the turtles were mostly swimming in such deep water that they had no chance of seeing the seafloor beneath them (they don’t normally dive deeper than 50m). In these circumstances it would be hard for them to make use of underwater topography to guide them. However, when they got close to their destinations and entered shallower water, they were able to head fairly directly towards them. This suggests that they were making use of ‘landmark’ information - possibly acquired on previous trips.

This study also compared what the real turtles did with what they might have done based two different assumptions about how they navigate.

The first, stringent assumption was that the turtles are true ‘map and compass’ navigators - able, that is, both to work out where they currently are and where they need to go to reach their goal.

The second, much simpler one was that the turtles only had access to a compass of some kind that would enable them to maintain a steady course. This would of course give them no positional information.

When the actual tracks followed by the turtles were compared with the ‘virtual tracks’ that emerged from the simulations, it became clear that the turtles were not perfect map and compass navigators. They lacked ‘the ability to always locate small isolated targets with pinpoint accuracy’.

But, since they were still able to find their targets, it looks as if the turtles must have access to some kind of ‘map’, though plainly not a very detailed or precise one.

Such a map is very likely to involve geomagnetic cues, though other factors might also be involved. (Ken Lohmann’s studies of captive loggerhead turtle hatchlings have already shown their acute sensitivity to geomagnetic information - see Incredible Journeys chapter 22 for a summary.)

It’s also clear that the turtles don’t rely on following a single, fixed compass course. This makes very good sense as such a crude mechanism would make them vulnerable to the disturbing effects of ocean currents that deflected them from their proper course..

The researchers found no evidence that, in the final stages of their journeys, turtles were making use of olfactory information - either smells in the air or tastes in the water - carried to them from their target. This is quite surprising, especially as hints of such an ability have emerged from earlier research.

This new study illustrates an important principle. Evolution doesn’t favour the emergence of perfect systems of navigation (or anything else), when merely adequate ones will enable animals to survive and reproduce successfully.

Good enough is good enough!