By George Whitman, who is dressed as Dr. John Watson this Halloween
While this Sherlockian mystery is fictional, it is inspired by a real event in which a Walleye was illegally introduced into Lake Cascade, Idaho. The events described below parallel the actual research conducted to uncover its origins.
Looking back over the notes of my many adventures with Sherlock Holmes, I cannot but reflect upon the remarkable variety of his methods. Some drew upon his intimate acquaintance with the whole annals of crime in London, while others depended on obscure knowledge such as the distinctions in ash produced by different varieties of cigar. Yet of all the cases solved through that extraordinary range of expertise, I can recall none in which he relied more wholly upon his mastery of the tools of science than in The Adventure of the Walleye Mystery.
My companion and I had taken a brief holiday upon the picturesque shores of Lake Cascade, in the distant state of Idaho. You may well wonder what chance or circumstance carried us to so remote a corner of the world, so far removed from the familiar comforts of our rooms at Baker Street. The explanation is a simple one: we were, at that time, still recovering from the exertions of a recent investigation commissioned by the Idaho State Board of Health which can be read in a soon to be published article under the title of The Adventure of the Poisoned Potato.
My colleague and I had heard much of Lake Cascade’s celebrated yellow perch fishery, and accordingly decided to rent rod, tackle, and boat, in the hope of securing a worthy specimen. The entire morning had passed without the slightest indication of a bite, and we were beginning to fear that the prime angling hour had already slipped away, when Holmes turned to me and, with his customary dry composure, remarked, “My dear Watson, I fear that our efforts today are…” Before he could finish, however, his line went taut and writhed with extraordinary violence.
My old friend instantly sprang into action and sharply pulled the rod with all his considerable strength, setting the hook. His quarry responded in kind, darting forth with such ferocity that the slender pole bowed alarmingly, as though it would snap in twain beneath the strain. The struggle that ensued resembled a duel of seasoned fencers; each furious lunge was met by a deft parry or a cautious retreat, the combatants evenly matched in skill and cunning. Minute by minute, the contest wore on. I noted with some concern the furrow that deepened upon Holmes’s brow. “Curious, most curious,” he murmured beneath his breath, his eyes never leaving the churning water. At last, the bout reached its conclusion. The considerable vigor of the beast had been spent, and it was reeled in. Holmes secured the creature within the net, encountering little resistance from his exhausted opponent, and carefully lifted it into the boat.
Holmes examined his prize with intense disquiet. “This fish should not be here,” he observed gravely.
“By what do you mean? Surely, where else would a fish be but in the water?” I exclaimed.
Holmes emitted a sigh of long-suffering and replied with his customary coolness, “My dear fellow, while your conjecture is correct that fish belong in the water, you fail to grasp the situation in its entirety. We set out today to catch Yellow Perch, but this specimen is a Walleye, scientific name Sander vitreus. You can tell by its large reflective eyes, long toothy jaws, olive and yellow coloration, and its slender but muscular frame.”
“It is renowned for the ferocity of its struggle on the line, which I may add, was my first indication that something was amiss. It is common enough across the upper reaches of North America, but here in Lake Cascade it is most assuredly an intruder and a threat to all that swim in this lake.”
“If some foolhardy soul has seen fit to transplant the creature from afar, that alone would be troubling enough. But should this scaly denizen have been born in these waters, should it be the fruit of a yet unknown breeding population, then we face a calamity. If allowed to multiply unchecked Walleye would quickly dominate the native stock here and devastate the entire fishery. I must get to the very roots of the matter without delay!”
In an instant and with a single, deft movement of his arm, he whirled the interloper into the side of the boat, dispatching it with a hangman’s efficiency, causing me to repress my shock at the suddenness of the act. He reached into the inner pocket of his ever-reliable overcoat and produced a slender case containing his investigative implements, because even at leisure, the extraordinary detective remained prepared to confront any puzzle, anomaly, or crime that might present itself. Amongst his tools he selected a set of fine tipped tweezers and inserted them between the gills and into the head of the now inert trespasser. From within the head he extracted a small white stone, no bigger than a child’s button.
“What the devil is that? A fish bone?” I enquired.
Holmes held up his find to the morning sun, examining it. “No, no, no,” he remonstrated. “It is something much better. This, my dear Watson, is the clue that will crack the case wide open! Quickly, I must return to shore and start work at once.”
Upon setting foot on dry land, Holmes turned to me with that air of brisk resolve. “I must beg your pardon, my old friend,” said he, with a trace of regret in his voice, “but we must, for the present, part company. The proper authorities must be apprised of this affair, and I have certain instruments to procure before the investigation can proceed. Once these matters are set in order, we shall resume our holiday forthwith.”
I heard nothing further of the affair of the Walleye after that moment. The matter seemed to have slipped entirely from Holmes’s conversation, and indeed from his thoughts, or so I believed. Some weeks later, when we had long since returned to London and our quarters at Baker Street, I found my companion seated before the hearth, lost in thought and wreathed in the familiar haze of pipe tobacco.
Unable to repress my curiosity a moment’s longer I interrupted his meditation, “My dear fellow, whatever became of that business of the Walleye?”
“Ah yes, that matter,” he mused, setting down his pipe. “As luck would have it, that particular individual was not a resident by birth of Lake Cascade, so there is no need to worry about exploding populations and a ruined habitat at this moment. It was, rather, conveyed by some misguided hand from a nearby reservoir two years past, when the creature itself was in the second year of life. The perpetrator, in all probability, acted in the desire to furnish the lake with their preferred sport.”
I could scarcely hide my astonishment. “How could you possibly know all that? Did it have something to do with that curious bone you pulled out of the creature’s head?”
Holmes donned the mischievous grin that often comes with his explanations. “What you are so quick to call a mere fish bone is in truth an otolith or, as the Greeks would have it, an ‘ear stone.’ It’s like a bone, but its composition is more akin to a coral or clam shell. For its original owner, it imparts a sense of orientation and movement, but to a trained scientist it tells a far deeper tale.”
“You see Watson, just as a tree grows one layer at a time and forms a pattern of rings, so too does an otolith. In fact, were I to show you a magnification of an otolith’s cross section you could scarcely tell the difference. And like a tree you can count these rings to derive its age. Our guest had exactly four such rings in its otolith, meaning it was precisely four years old.”
“That appears to be in perfect order,” I ventured, “but pray, Holmes, how did you deduce its source and the year of its passage?”
Holmes replied with a wry smile, “Any student of geology can tell you that a river or lake will take on a unique elemental signature depending on the surrounding minerals. What is less appreciated is that fish are inscribing this signature into the crystalline matrix of their otoliths every day. It is, if you will permit the analogy, as though each of them carries within their own bodies a waterproof diary, in which they faithfully record the story of their days beneath the surface. One only requires the means to read it.”
I confess that I was at a complete loss. “Read a fish’s diary?” I cried in astonishment. “My dear Holmes, how in the world does one even begin to go about such a thing?”
“It is simplicity itself, my dear Watson,” said Holmes. “One must first extract minute quantities of the otolith’s substance, whether by a lilliputian drill bit or by the precision of a laser beam. This material is then submitted to the examination of a mass spectrometer, which reveals the elemental composition within.”
“By comparing the elemental signature found in the otolith with that of the surrounding waters near the point of its capture, I could deduce the locality in which the creature sojourned at any given period of its existence. With this data in hand, I observed a marked alteration in its chemical character between the second and third annular rings. From that evidence, it was perfectly clear that this clandestine transport occurred during the second year of life. Unfortunately the evidence, though most illuminating, does not extend to the identity of the culprit who wanted to introduce a species where it does not belong.”
I turned his words over in my mind for a moment before remarking, “Once explained, it seems absurdly simple.”
“Quite so,” Holmes replied, with a faint smile. “The simplicity of a matter, my dear Watson, is rarely apparent until all the facts are before oneself. The true difficulty, I fear, now rests with the game managers of Idaho. There is currently no evidence that Walleye are gaining a foothold in Lake Cascade, but that doesn’t mean it will remain so in perpetuity. It will fall to them to see that any future intrusions are quickly removed.”
“But for our part, it was all quite… elementary.”
As It Happened, Without Embellishment: The Singular Case of the Real Walleye Mystery
Chris Weber and Mike Thomas caught the real Walleye with hook and line then brought it to the Idaho Department of Fish and Game where its otoliths were removed. One of those otoliths was sent to the Center for Watershed Sciences at UC Davis where it was thin sectioned in preparation for isotopic analysis and its age was determined. The otolith was analyzed for strontium isotopes at the UC Davis Interdisciplinary Center for Plasma Mass Spectrometry using a multi-collector ionically coupled plasma mass spectrometer.
Like in the Sherlock Holmes version of this tale, the analysis revealed that the Walleye had been transplanted from outside of Lake Cascade roughly two years before its capture. In neither case, real nor imagined, was the perpetrator of the introduction ever identified.
Legal
All copyrights of the original Sherlock Holmes stories by Sir Arthur Conan Doyle have expired as of January 2023 and are in the public domain pursuant to 17 U.S.C. § 302.
About the Author
George Whitman is a researcher at the Center for Watershed Sciences and longtime otolith aficionado. He can be contracted at gewhitman@ucdavis.edu. George Whitman is also the illustrator of the Sherlock-walleye figure in this post.
Further reading
Read the original published journal article about the Walleye mystery:
Whitman, G., Messner, J., Johnson, R.C., Willmes, M., Kennedy, B.P. and Jeffres, C., 2024. Forensic geochemistry identifies the illegal introduction of Walleye into Lake Cascade, Idaho. North American Journal of Fisheries Management, 44(2), pp.407-414. https://doi.org/10.1002/nafm.10985
Learn more about otoliths and the research tools that involve them:
Reis-Santos, P., Gillanders, B.M., Sturrock, A.M., Izzo, C., Oxman, D.S., Lueders-Dumont, J.A., Hüssy, K., Tanner, S.E., Rogers, T., Doubleday, Z.A. and Andrews, A.H., 2023. Reading the biomineralized book of life: expanding otolith biogeochemical research and applications for fisheries and ecosystem-based management. Reviews in Fish Biology and Fisheries, 33(2), pp.411-449. https://doi.org/10.1007/s11160-022-09720-z
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