When whales were fish

Taxonomy in the 18th century struggled with how to define whales and dolphins. But even after science had reached a consensus, popular imagination continued to wonder: is a whale a fish?

 Illustration by Ruby Farukee

Illustration by Ruby Farukee

On December 31, 1818, lawyer William Sampson walked into the New York courtroom with the confidence of one ready to fight the elite. He had already experienced imprisonment and violence in his native land of Ireland, before he was exiled to the continent and eventually moved to the United States. His partner Mr Anthon gave the opening statements: “It is fortunate…that this statute is not to be interpreted according to the refined and learned opinions of naturalists…but [is] to receive an interpretation according to their common and popular usage.”

While scientists quibbled over terms, functions, and definitions, laypeople had the common sense to know: a whale was a fish.

Sampson and Anthon represented the fish oil inspector James Maurice against a whale oil businessman named Samuel Judd. A recent shipment had arrived of new sperm whale oil. Candlemaker and oil merchant Samuel Judd had purchased three barrels of oil, but inspector Maurice claimed Judd owed fines on the oil in accordance with fish oil law. Since Judd had avoided the inspection, he owed the city a $75 fine. But Judd claimed that whales were not fish, and he did not need to pay the fee. When he still refused to pay, Maurice brought Judd to court.

As the largest creature of the water, common sense would probably lead most 18th century laypeople to conclude that whales were fish. Whales, dolphins, and fish all share a similar torpedo-like shape, smooth skin, and thick fins. They swim deep under the water and only surface for moments, shooting streams of water into the air. They dive, jump, and leap through the water. They are the kings of the oceans.

The entire court case hinged on a single question: is a whale a fish? Each side would parade a litany of names in front of the jury. But for the star expert witness, a medical doctor and natural historian named Dr Samuel Mitchell, the answer was simple: “As a man of science, I can say positively that a whale is no more a fish, than a man; nobody pretends to the contrary now-a-days, but lawyers and politicians.”

  Whales have fascinated human onlookers since antiquity, but as this 1617 painting shows, misconceptions about whale anatomy persisted for centuries .  Esaias van de Velde/Wikimedia Commons  (public domain

Whales have fascinated human onlookers since antiquity, but as this 1617 painting shows, misconceptions about whale anatomy persisted for centuries. Esaias van de Velde/Wikimedia Commons (public domain


Nevertheless, science has not always been so confident about the nature of classification. When Pliny divided animals into three major categories, terrestrial, aquatic, and insect, he classified animals according to their environment; and the deep oceans held mysterious creatures. He wrote, “In the seas, spread out as they are far and wide, forming an element at once so delicate and so vivifying, and receiving the generating principles from the regions of the air, as they are ever produced by Nature, many animals are to be found, and indeed, most of those that are of monstrous form.”

These monsters included the “balenae”, dolphins, and orcas — which breathed with lungs, whereas other fish used gills. Roman polymath Pliny the Elder described whales as such: “Balænæ have the mouths in the forehead; and hence it is that, as they swim on the surface of the water, they discharge vast showers of water in the air. It is universally agreed, however, that they respire, as do a very few other animals in the sea, which have lungs among the internal viscera; for without lungs it is generally supposed that no animal can breathe.”

  This wood engraving of “seventeen fishes” includes a “whale” and a “sea unicorn” or narwhal.   I. Taylor/Wellcome Collection  (public domain)

This wood engraving of “seventeen fishes” includes a “whale” and a “sea unicorn” or narwhal. I. Taylor/Wellcome Collection (public domain)

Despite their habit of respiring air, whales and other large creatures of the sea remained a mysterious fish for ancient writers.

It was not until the 18th century that scientists began to systematically investigate how to classify the animal kingdom. The shape of the animal came to matter less, and scientists judged categories based on organ interaction and structure. The great taxonomist Carolus Linnaeus embarked on this transformation with his publication System of Nature. “I have submitted with patience to the scoffs of the ignorant and the malicious, who have either contemned the objects, or envied the success, of my laborious pursuits.”

He first published the method in 1735 and explained that his method required naming. To name something was to investigate its nature. Just as streams lead to rivers and lakes and larger bodies of water, so too did names organise the various parts of the world. He said, “The framer of a systematic arrangement begins his study by the investigation of small details.” To accomplish this process, Linnaeus examined the animal as a machine. The parts of the animal could then be divided into systems, like an engine, where each group was composed of its functioning parts, or in biological nomenclature, the organs.

And what were these particulars? As Linnaeus visited museums and collections around Sweden, he studied individual specimens and divided animals into six classes: Mammals, Birds, Amphibians, Fishes, Insects, and Worms. Mammals and birds were grouped together since they both had a four-chambered heart and warm blood. Amphibians and fishes were next grouped together since they were cold-blooded and had a heart composed of a single auricle and ventricle. Finally, insects and worms formed the final set, because they had a single auricle and ventricle and were cold-blooded.

Additional criteria based on functions defined the classes. For instance, mammals gave birth to live young, meaning mammals were viviparous, and the birds gave birth by eggs, making them oviparous. Linnaeus also pointed out that mammals milked their young, walked on four legs, and were mostly covered in fur.

Whales, however, were not so easily categorised. When Linnaeus introduced this group, he wrote, “All the animals of this order more readily bring to mind the Quadrupeds than the Fish, when we consider their internal structure: lungs, respiration, breasts, feet, appendages, live birth, etc. all indicate as much. We attach them, nevertheless to the Fishes by reason of their habitus, their medium, their swimming, etc. in order not to fall from Charybdis into Scylla.”

Thus, despite all the anatomical evidence showing that whales ought to be organised with mammals, Linnaeus felt common-sense forced him to class them with fish.

  Many folktales, such as that of St. Brendan, conflated whales with very large fish. This illustration of a whale from circa 1621 clearly shows a beast with scales.   Chet Van Duzer/Wikimedia Commons  (public domain)

Many folktales, such as that of St. Brendan, conflated whales with very large fish. This illustration of a whale from circa 1621 clearly shows a beast with scales. Chet Van Duzer/Wikimedia Commons (public domain)


Over in France, naturalist Mathurin-Jacques Brisson was less convinced. Brisson was also interested in organising the animal kingdom in a systematic method that drew on empirical investigation of animal systems and organs. Working in the backrooms of the 18th century French “Cabinets”, the forerunners of museum collections, Brisson examined natural history specimens “which have daily set before my eyes the richest collections of nature’s production.”

Analogy helped Brisson categorise the animals. He thus defined creatures in terms of their relationship to the human body and divided them according to their blood, lungs, ventricles, reproduction, hair or fur, and number of appendages. By subtracting the number of similar analogies to human anatomy, Brisson identified nine classes: quadrupeds, cetaceans, birds, cartilaginous fish, fish, reptiles, crustaceans, insects, and worms.

Anatomy helped Brisson differentiate between similar animals. For instance, instead of including all marine creatures under the fish class, Brisson distinguished sharks and other cartilaginous fish compared to other fish. He followed the same strategy with whales. “Like the Quadrupeds, Cetaceans have two ventricles in the heart; breath with lungs; couple, give birth to live young, and milk their young,” he wrote. “They also resemble the Quadrupeds by their structure and use of their internal organs.”

Why then were they not classed with the other mammals? Again, the reason was their environment. “All the animals of this class always live in the water, and they never leave, without risking their lives,” Brisson wrote.

Museum “cabinets”, however, could only offer so much to natural scientists. Brisson was only able to examine a few cetaceans in the natural history collections. It would not be until 1787 when the whaling industry began to take off that natural history had more direct information on whales.

Before kerosene and the discovery of petroleum, whale oil lit the world and was the engine of industrialisation. Although a dangerous enterprise, hunting blubbery whales could yield huge profits.

Natural scientists like John Hunter commissioned other “scientific minds,” to help them collect specimens for dissection and further investigation, for “the animals which inhabit the sea are much less known to us than those found upon the land.” Hunter commissioned one surgeon on a whale ship to Greenland to bring back a specimen. The surgeon had difficulty, and “the only return I received for this expense was a piece of whale’s skin, with some small animals sticking upon it.” His protégé Edward Jenner, who would go on to become a vaccine pioneer, sent him another sample which originated off the coast of England.

  Mathurin-Jacques Brisson was one of the first naturalists to emphatically argue that whales were not fish .  Wikimedia Commons  (public domain)

Mathurin-Jacques Brisson was one of the first naturalists to emphatically argue that whales were not fish. Wikimedia Commons (public domain)

After Brisson published his book, Linnaeus was inspired. He opted to go one step further: “This order of Cete [which includes whales and dolphins] ought...to have been arranged with the class of Fishes; but … employing the circumstance of suckling their young as a characteristic mark for a number of animals, [I have included] these [as mammals].” Linnaeus then became the first to claim that whales were indeed mammals in his ninth edition.

Brisson felt cheated. Published soon after Linnaeus’ 1756 edition, Brisson wrote in his new volume on birds, “Following my example, [Linnaeus] replaced Cetaceans under the Quadrupeds, by reason that they suckle their young; but so as to appear he did not copy me, he placed them in the same class [as mammals], a fact which I do not find tenable.” Even as organ structure and biological systems came to replace classical differences, whales challenged scientists’ judgments. The environment must have played a factor, to make whales either related to fish or as a separate marine animal. How could they be mammals?

For scientists, the answer came with access to more specimens. The medical doctor John Hunter was able to justify Linnaeus claims that the whale and its relatives were mammals. He conducted 12 dissections on the various whale specimens collected from around the world. He even had examples of that rare white whale: the balaena mysticetus, or the Sperm Whale.

Because some of the whales were used for oil, he was unable to dissect every animal in its entirety, thus only some were examined “with accuracy” while others were only “superficial.” Nevertheless, Hunter concluded, “This order of animals has nothing peculiar to fish, except living in the same element, and being endowed with the same powers of progressive motion as those fish that are intended to move with a considerable velocity…Although inhabitants of the waters, they belong to the same class as quadrupeds, breathing air, being furnished with lungs, and all the other parts peculiar to the economy of that class, and having warm blood.”

By the 19th century, the scientific community had largely reached a consensus: whales were mammals and not fish. Other studies continued to substantiate the evidence. Yet, the question needed to be repeated, because the answer was not so intuitive to those not absorbed in the pursuit of scientific study.

  In the early 19th century, the northeastern United States was home to a thriving whaling industry, which produced enormous amounts of ‘fish oil’ .  Elmo Paul Hohman/Wikimedia Commons  (public domain)

In the early 19th century, the northeastern United States was home to a thriving whaling industry, which produced enormous amounts of ‘fish oil’. Elmo Paul Hohman/Wikimedia Commons (public domain)


Back in the New York courtroom, the defense called physician and naturalist Dr Mitchell to the stand as an expert witness. Arriving a little after five o’clock, Dr Mitchell explained that fish oil and whale oil were treated differently by businessmen. While artisans and manufacturers distinguished them based on the nature or character of their oil, “as far as human discoveries have gone, and human research penetrated, it is received as an incontestable fact in zoology, that a whale is no fish.” And with that, the defense said, “No further questions your honor.”

Nevertheless, the question before the jury was a legal one and not a scientific question. Other witnesses pointed out the flexible use of the term ‘fish’. One stated, “Fish oil means all sorts of marine oil…and I have known of deceptions and frauds in whale oil. I think it requires inspection to put an end to them.” Losee Van Ostrand, a leather dealer and currier, said. “I consider the word, fish oil, as meaning every kind of marine oil. If there is no liver to be had, we use the others, whale and all mixed together. Strained oil is called fish oil; there is a difference made between cod liver oil, and fish oil of other fishes' livers, but the general word, fish oil, embraces all.”

William Sampson and his team representing the fish oil inspector admitted that science held that whales were mammals. But, they argued, “such a construction of a statute would be in opposition to the well-established rules of the common law.” The lawyers explained, “applying this plain rule to this case, all refined theories are at once put to flight, and the words ‘fish oils’ must be considered as embracing the oil of the whale, as well as that of any other fish.”

“Common sense” won the day. After closing statements, the jury retired. In fifteen minutes, they returned with their verdict in favour of the plaintiff and demanded the defendant pay the penalties. Even after all the debates over how to classify cetaceans, in 1818, a whale could still be a fish.

Edited by Diana Crow