REMINISCENCES | How do sperm whales locate giant squid?

REMINISCENCES | How do sperm whales locate giant squid?

Photo: National Museum of Nature and Science of Japan/Tsunemi Kubodera

My hypothesis (theory) on how sperm whales locate giant squid is that, in addition to using their biosonar, sperm whales locate giant squid by listening for sounds made by squid as they pulse their funnels when moving fast or making quick changes in directions.

This episode is different than all other episodes in this memoir because it is a short version of a formal scientific paper on sperm whales vs giant squid that I submitted to two scholarly journals in 2011. Both the Journal of the American Society of Acoustics and the Journal of Marine Mammal Science rejected it, although one reviewer thought “it was an interesting idea”.

The main comment made by three reviewers was that the paper was essentially speculative. “The manuscript is too long given the lack of solid information on the topic,” said one reviewer. Another said if the paper was drastically shortened it might be publishable.

“I applaud the author for putting the ideas together in one place,” another said. “Perhaps it could be published in a magazine or on-line.”

“The hypothesis (theory) that sperm whales hunt by passive listening is not too outlandish,” said another.

Technically speaking, my paper was rejected because of the lack of evidence and my missing several relevant citations. My reaction to the rejections was to put my paper aside and revise and shorten it later when time permits. I therefore put the paper in my LBW file (Let the Blighter Wait) and turned my attention to researching and writing on the mental health of seafarers, which in many cases is not very good. This effort was part of a seafarer’s mental health project of the Rotary Club of Melbourne South (Australia), of which I am a member.

“I think this episode could easily be turned into a magazine article on sperm whales using passive listening to locate giant squid.”

It has been almost nine years since I wrote my long sperm whale vs giant squid paper and started writing this memoir. When I had completed 75 per cent of the memoir, it occurred to me that one way to get my theory of sperm whales listening for sounds made by giant squid before a different audience would be to turn my formal paper into a memoir episode.

I realise doing this may not go down very well with some sperm whale vs giant squid researchers, but at age 92, I am not concerned about that. As suggested, I think this episode could easily be turned into a magazine article on sperm whales using passive listening to locate giant squid.

I was prompted to study sperm whales vs giant squid by two separate events. One was that I recorded sounds made by three small squid (45, 45- and 65-mm mantle length) during a cruise by the research vessel Hugh M. Smith in 1957 on the equator south of Hawaii (How these squid were captured is described in another memoir episode). These sounds were subsequently published in a paper in the journal Nature by me and two US Navy Chief Sonar Technicians. It contained a spectrogram of a burst of the sounds thought to have been made by the small squid. The frequencies of the burst were from 1,500 to 2,400 cycles per second (hz).

The second event involved the findings of three Japanese scientists on the of wild hunting behaviour and bioluminescence of a large eight-armed squid and published in 2005 in the Journal of the Acoustical Society of America and in 2007 in the Proceedings of the Royal Society B (United Kingdom). They used a newly developed underwater high definition video camera system to take the first live images of adults from the large squid Taningia danae photographed at depths of 240 and 940 metres off the Ogasawara Islands in the Western North Pacific. They also photographed two species of the giant squid Archituethis.  These remarkable photos show the giant squid Taningia danae attacking the bait and manoeuvring its body to grasp the bait. One of the Archituethis squid lost an arm when it impaled itself on the hook holding the bait.

Sounds produced by giant squid should be more intense (louder) than those of small squids. I base this on the fact that their funnels, also called siphons, are huge compared to the funnels of small squid. But their function is the same in both giant squid and little squids – they are used for jet propulsion.

“The ability of sperm whales to listen for sounds made by giant squid or other prey should improve their searching behaviour.”

How powerful are giant squids and other large squids? Anecdotal and circumstantial reports have shown these deep-sea squid are very powerful! Lane reported they are capable digging trenches in beaches when stranded. He cites an 1879 account by Yale University professor of zoology A. E. Verrill, who discovered that a 45-foot-long giant squid (Architeuthis species) that was stranded at Trinity Bay (Connecticut, USA) struggled violently in an attempt to escape. “The squid ploughed a deep trench in the beach about 30 feet long,” Verrill is quoted saying. I think this means the giant squid was stranded in a few inches of water.

Lane also cites a report by John Manning, who fished for large Humboldt Current squids (Omamastrephes gigas) for the Lerner Marine Laboratory, as saying “The discharge from the funnels of these squids is about like the blast from a fire hose.”

How fast can giant squid swim? Lane cites another unusual account published in 1946 in the journal Natuten of the Bergen Museum in Norway that described the swimming speed with which giant squid swam alongside while “attacking” the 15,000-ton tanker Brunswick sailing between Hawaii and Samoa. Commander Arne Groenningsaefer of the Royal Norwegian Navy was the executive officer of Brunswick and viewed the giant squids from his vantage point on the ship’s bridge about 15 metres above the sea surface. He is quoted as saying, “the Brunswick’s speed was 12 knots, so the squids speed was probably 20 miles per hour.”

Commander Groenningsaefer is also quoted as saying, “This happened on three occasions during the years 1930 and 1933 by giant squids, each time between Hawaii and Samoa.” As far as I’m concerned, to maintain such a speed, the water ejected from the squid’s funnel would have to be very powerful.

Could sperm whales hear sounds made giant squid? The lack of data on hearing thresholds in sperm whales is firstly due to the size of sperm whales – thus far no one has kept them in condition suitable for to testing, and secondly the general lack of any specific information on sperm whale hearing ability – other than the assumption that sperm whales can hear whatever frequency they use for echolocation when the signal is reflected back to them. Future research to record and describe the frequency of any sounds made by giant squid as well as the presence, or absence, of sperm whale phonations in areas where giant squids are lacking, could help prove or disprove whether giant squid produce sounds that sperm whales might hear and/or listen for them.

From an evolutionary standpoint, the ability of sperm whales to listen for sounds made by giant squid or other prey should improve their searching behaviour. Research describing the frequencies and intensities of sounds made by giant squid should help understand the possible use of squid sounds by sperms whales to capture giant squid. I recommend that future attempts to photograph giant squid in situ include equipment to record any sounds made by giant squid. Because the hypothesis that giant squid make low frequency sounds is, inter alia, based on circumstantial and anecdotal evidence, this report should be considered speculative.

The above article is an excerpt from Swimming with Fishes, Dr Bob Iversen’s memoir detailing his experiences as a fishery biologist. It is reposted here on Baird Maritime with the author’s permission.

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Bob Iversen

Bob Iversen is a retired Hawaii fishery biologist who spent 40 years studying tuna and other fish in the tropical Pacific Ocean. He is a former officer in the US Navy, and initiated the “mental health of seafarers” movement that has now taken off worldwide.