Whales did this in the Middle Ages too, study finds

In 2011, scientists recorded a previously unknown feeding strategy in whales around the world. Now, researchers in Australia think they may have found evidence of this behaviour being described in historical accounts of sea creatures, including from the Middle Ages. They believe that misunderstandings of these descriptions contributed to myths about medieval sea monsters.

Whales are known to lunge at their prey when feeding, but recently whales have been spotted at the surface of the water with their jaws open at right angles, waiting for shoals of fish to swim into their mouths. A clip of this strategy was captured in 2021 and went viral on Instagram.


This strategy seems to work for the whales because the fish think they have found a place to shelter from predators, not realising they are swimming into danger. It’s not known why this strategy has only recently been identified, but scientists speculate that it’s a result of changing environmental conditions – or that whales are being more closely monitored than ever before by drones and other modern technologies.

Dr John McCarthy, a maritime archaeologist in the College of Humanities, Arts and Social Sciences at Flinders University, first noticed intriguing parallels between marine biology and historical literature while reading about Norse sea monsters.


“It struck me that the Norse description of the hafgufa was very similar to the behaviour shown in videos of trap feeding whales, but I thought it was just an interesting coincidence at first,” says Dr McCarthy. “Once I started looking into it in detail and discussing it with colleagues who specialise in medieval literature, we realised that the oldest versions of these myths do not describe sea monsters at all, but are explicit in describing a type of whale. That’s when we started to get really interested. The more we investigated it, the more interesting the connections became and the marine biologists we spoke to found the idea fascinating.”

Medieval depiction of a whale-like creature with fish jumping into its mouth – Icelandic Physiologus (ca. 1200) depiction of the Apsido feeding (Reykjavík AM 673 a II 4to fol. 3v; Public Domain; color and contrast corrected).

Old Norse manuscripts describing the creature date from the 13th century and name the creature as a ‘hafgufa’. For example, the Konungs skuggsjá, a text composed for the Norwegian King Hákon Hákonarson (1217–1263), gives this overview of the creature

There is one fish yet to be accounted, and I am rather reluctant to tell of it because of its great size, which most people will find unbelievable. Few people can say anything clear about it, for it is seldom near land or in the sights of fishermen, and I do not expect that there are many such fish in the sea. We usually call it the hafgufa in our tongue…. It is said of the nature of this fish that, when it goes to feed, it gives a great belch out of its throat, along with which comes a great deal of food. All sorts of nearby fish gather, both small and large, seeking there to acquire food and good sustenance. But the big fish keeps its mouth open for a time, no more or less wide than a large sound or fjord, and unknowing and unheeding, the fish rush in in their numbers. And when its belly and mouth are full, [the hafgufa] closes its mouth, thus catching and hiding inside it all the prey that had come seeking food.

This creature remained part of Icelandic myths until the 18th century, often included in accounts alongside the more infamous kraken and mermaids.


However, it appears the Norse manuscripts may have drawn on medieval bestiaries, a popular type of text in the medieval period. Bestiaries describe large numbers of real and fantastical animals and often include a description of a creature very similar to the hafgufa, usually named as the ‘aspidochelone’.

Both the hafgufa and aspidochelone are sometimes said to emit a special perfume or scent that helps to draw the fish towards their stationary mouths. Although some whales produce ambergris, which is an ingredient of perfume, this is not true of such rorquals as the humpback. Instead, researchers suggest this element may have been inspired by the ejection of filtered prey by whales, to help attract more prey into a whale’s mouth.

Diagram of humpback engaged in trap feeding; with a jaw either flush with the waterline, or raised to a similar height to the rostrum. Image by John McCarthy, Flinders University

Other descriptions of this behaviour date back as far as 300 BC. Why it has not been seen again until very recently might be because whale populations had fallen greatly in the last few hundred years because of human hunting, and have only now begun to recover. The researchers write:


In this scenario, trap or tread-water feeding behavior would not be an animal kingdom “invention” of the 21st century, but rather an occasional strategy with much deeper roots. The lack of scientific observations prior to the last two decades might be explained by the relative rarity of this feeding strategy, or alternatively because the strategy was not being used. Niche hunting strategies like trap feeding and lobtail feeding may have been rendered largely unnecessary when whale populations crashed and competition for fish reduced. 

Research co-author Dr Erin Sebo, an Associate Professor in Medieval Literature and Language in the College of Humanities, Arts and Social Sciences at Flinders University, says this may be another example of accurate knowledge about the natural environment preserved in forms that pre-date modern science.

“It’s exciting because the question of how long whales have used this technique is key to understanding a range of behavioural and even evolutionary questions,” Dr Sebo says. “Marine biologists had assumed there was no way of recovering this data but, using medieval manuscripts, we’ve been able to answer some of their questions.

“We found that the more fantastical accounts of this sea monster were relatively recent, dating to the 17th and 18th centuries and there has been a lot of speculation amongst scientists about whether these accounts might have been provoked by natural phenomena, such as optical illusions or under water volcanoes. In fact, the behaviour described in medieval texts, which seemed so unlikely, is simply whale behaviour that we had not observed but medieval and ancient people had.”


The article, “Parallels for cetacean trap feeding and tread-water feeding in the historical record across two millennia,” by John McCarthy, Erin Sebo and Matthew Firth, is published in Marine Mammal Science. Click here to read it.

Top Image: A digital reconstruction of a humpback whale trap feeding. Image by John McCarthy, Flinders University