In 1983, two scientists, one from California and one from Denmark, co-authored a research paper titled "Can odontocetes debilitate prey with sound?" Odontocete is a fancy term for toothed whales (the group that includes sperm whales, orcas, and dolphins) and so the question could be written thus: Can toothed whales stun their prey with loud noises?

The idea is a fascinating one, and not too surprisingly, it has caught the public imagination. Sometimes, however, the all-important question mark is omitted, and the statement is taken as fact. It is important to bear in mind the first paragraph of the article:

In this paper we discuss an hypothesis. We marshall scattered supportive evidence, outline its problems, and explore its ramifications and suggest tests. We do not prove it.

Norris and Mohl, the authors of this paper, are also clear that they are not the first to suggest the hypothesis. Their contribution is to synthesize the evidence and suggest future directions. They stress that:

The major problem for the hypothesis is the lack of recordings of such very intense odontocete sounds at sea.

That means they don't know whether toothed whales do, in fact, make loud noises. That's one problem. The other major problem for the hypothesis is that they also don't know whether loud noises can, in fact, stun squid.

That was almost almost thirty years ago, and those seem like pretty basic questions. Surely we have some answers by now?

To find out whether or not toothed whales make loud noises, scientists have done a lot of whale eavesdropping. They've heard whales make a lot of sounds, and they've described those sounds (biologists are very good at describing things), and made some educated guesses about what purposes the sounds serve. But it's astonishingly difficult to make any confident statements about exactly how the sounds relate to hunting behavior.

I'm going to focus on sperm whales now, quoting from the introduction of a paper published by Miller et al. in 2004:

It is widely accepted that sperm whales forage during deep dives that routinely exceed a depth of 400 m and 30 min duration, but many different hypotheses exist concerning the precise mechanisms by which sperm whales locate and capture prey.

The authors go on to say that there is "increasingly strong" evidence that sperm whales use echolocation to find prey. This is the same technique made famous by bats and dolphins, and consists of emitting regular sounds and listening for the echoes bouncing back. From the echo, they can determine the type of object it bounced off of (rock, fish, squid) and how far away it is.

That's all well and good, but what about capturing prey? What about stunning squid with sonic blasts? Any progress on that?

In a word, no.

The closest I can find is a 2003 paper by Mohl (one of the authors of that original 1983 paper) and colleagues, in which they present recordings of sperm whale clicks that are

by far the loudest of sounds recorded from any biological source.

Well! That sounds promising! Except . . . they don't mention the Norris and Mohl theory of stunning prey with loud noises. They don't even cite that paper. So maybe that theory has fallen out of favor? Maybe Mohl forgot about it (unlikely)? Maybe I'm missing something?

Anyway, that's the best I can do with Problem #1: Do toothed whales make loud noises? On to Problem #2: Can loud noises stun squid?

This was a tremendous black box in 1983, as the "deaf cephalopods" debate hadn't even gotten started yet. I've mentioned this before, but just to sum up:

In 1985 a fellow named Moynihan wrote an article called “Why are Cephalopods Deaf?” in which he argues that the sophisticated visual communication system of cephalopods provides all the benefits you’d expect from acoustic communication, rendering hearing unnecessary. Moynihand went on to suggest that deafness is actually selected for, as protection from the physically damaging sounds that can be produced by hunting cetaceans (citing the Norris and Mohl theory).

The follow-up, of course, is Hanlon's “Why Cephalopods are Probably Not Deaf” published a couple of years later, in which he summarizes the evidence that cephalopods can, in fact, detect and respond to underwater vibration.

In the intervening years, there's been a good deal less research into cephalopod hearing than there has into cetacean vocalization. But what research there has been is much more to the point.

In fact, a 2007 study from Wilson (with our pal Hanlon as co-author) precisely addresses our Problem #2. The title is "Intense ultrasonic clicks from echolocating toothed whales do not elicit anti-predator responses or debilitate the squid Loligo pealii" and that is pretty much all we need to know.

Well, okay, a little more information. They exposed squid to clicks as loud as those reported by Mohl et al. (that "loudest of sounds" paper), and after seeing no effect whatsoever on the squid, concluded that whales use these loud clicks only to detect squid, not to stun or debilitate them.

Pretty compelling. But . . . it's only one species of squid. And it's near-shore Loligo, which is a rather different kind of squid than open-ocean species like Dosidicus (Humboldt squid) or Architeuthis (giant squid).

So do I think the case is closed? Not really. Frustrating? You bet! Norris and Mohl's paper came out the year I was born, and now I have a PhD, and I still can't say definitively one way or the other.

Welcome to ocean sciences, where progress is slow and patience is a virtue.


Citations
Norris, K.,&Mohl, B. (1983). Can Odontocetes Debilitate Prey with Sound? The American Naturalist, 122 (1) DOI: 10.1086/284120
Miller, P., Johnson, M., & Tyack, P. (2004). Sperm whale behaviour indicates the use of echolocation click buzzes 'creaks' in prey capture Proceedings of the Royal Society B: Biological Sciences, 271 (1554), 2239-2247 DOI: 10.1098/rspb.2004.2863
Møhl, B., Wahlberg, M., Madsen, P., Heerfordt, A., & Lund, A. (2003). The monopulsed nature of sperm whale clicks The Journal of the Acoustical Society of America, 114 (2) DOI: 10.1121/1.1586258
Wilson, M., Hanlon, R., Tyack, P., & Madsen, P. (2007). Intense ultrasonic clicks from echolocating toothed whales do not elicit anti-predator responses or debilitate the squid Loligo pealeii Biology Letters, 3 (3), 225-227 DOI: 10.1098/rsbl.2007.0005