The Shark That Was Born Before Bach

A female Greenland shark hauled out of a fishing net in the North Atlantic measured 502 centimetres from snout to tail [S1]. When biologists carbon-dated the protein crystals in the nucleus of her eye lens, the number that came back was 392 ± 120 years [S1]. The confidence interval is wide for a reason — the upper bound is 512 — but even the floor puts her birth before the founding of the United States [S1].

The eye-lens trick, published by Nielsen and colleagues in Science in 2016, is the only thing that works on this animal [S1]. The embryonic nucleus of a vertebrate eye lens is laid down before birth out of crystalline proteins that are metabolically inert: the cell stops swapping them out, and they preserve the atmospheric ¹⁴C signature of the year the animal was conceived [S1]. For 28 female sharks landed as bycatch, that signature is a birth certificate written in carbon [S1].

You need the trick because every conventional method fails. Greenland sharks are cartilaginous, so they have no otoliths — the ear-stones whose growth bands fish biologists usually count — and their vertebrae are too soft to read like tree rings [S1]. They grow roughly half a centimetre to a centimetre a year [S1]. A four-metre adult is just a slow accumulation of millimetres.

Only the smallest sharks in the study, those 220 cm or under, carried the diagnostic bomb-pulse spike from atmospheric nuclear testing in the early 1960s, which is the one fixed point in the marine ¹⁴C record [S1]. Everything older is extrapolation from a calibration model, which is why the 392-year number comes with a ±120 envelope [S1]. The headline "400-year-old shark" is real, but it is not the tight measurement people think it is.

What the dating does pin down is when these animals start reproducing. Females reach sexual maturity at a total length of about 4.19 metres, which corresponds to roughly 150 years old [S1]. A Greenland shark spends its first century and a half as a juvenile.

Now the chemistry. The shark's flesh is loaded with trimethylamine N-oxide, an osmolyte that stabilises cellular proteins against the pressure and near-freezing temperatures of deep water, at concentrations far higher than in other sharks [S4]. The problem is what TMAO becomes on digestion: trimethylamine, the molecule that produces the smell of spoiled fish [S4]. Sled dogs fed raw Greenland shark meat develop what Greenlanders call shark drunkenness — disorientation, stumbling, convulsions — and Anthoni and colleagues identified TMA as the toxic principle in 1991 [S4].

This is why hákarl exists. The Icelandic dish detoxifies the meat by burying or boxing it for six to twelve weeks while bacteria convert TMAO into TMA and dimethylamine; TMAO falls below detectable levels in about five weeks, after which the flesh is air-dried for several months so the volatile amines and ammonia evaporate [S4]. The taste is famously unpleasant. The chemistry is a fish solving a pressure problem with a molecule that happens to be neurotoxic at the surface.

Then the eyes. A copepod called Ommatokoita elongata — pinkish-white, about 30 millimetres long — anchors itself to the cornea of an estimated 99% of adult Greenland sharks [S2]. Borucinska and colleagues sectioned the eyes of six infected animals in 1998 and documented corneal ulceration, keratitis, mineralisation of Bowman's and Descemet's membranes, fibrosis of the corneal substantia propria, and anterior uveitis [S2]. Their conclusion was that the infestation could produce "severe vision impairment (possibly including blindness)" [S2].

The shark does not appear to mind. Olfactory bulbs account for roughly 33% of its brain mass, and it hunts by smell and lateral line in water deep enough and dark enough that vision is largely redundant [S6]. A romantic theory dating to Berland in 1961 held that the copepod might be bioluminescent and lure prey toward the shark's mouth in a mutualistic arrangement; nobody has ever observed light coming off Ommatokoita, and specialist reviews now treat the idea as unlikely [S6].

Even the way the animal moves is strange. Watanabe and colleagues tagged six free-swimming sharks weighing 204 to 343 kilograms off Svalbard and recorded a mean cruising speed of 0.34 metres per second and a tail-beat frequency of 0.15 Hz — both the lowest values ever measured for a fish of that size [S3]. The maximum burst was about 0.74 m/s [S3]. Seals turn up regularly in Greenland-shark stomachs, but seals swim faster than 0.74 m/s, so the leading hypothesis is that the sharks are ambushing sleeping individuals [S3]. The hypothesis is untested.

Put it together. A near-blind, slower-than-its-food predator that takes 150 years to make its first baby is being hauled out of the North Atlantic by trawlers, longliners and gillnetters at a rate of roughly 3,500 individuals a year as bycatch [S5]. The IUCN reclassified the species from Near Threatened to Vulnerable in 2020 and estimates a population decline of about 60% over the past 420 years — roughly one Greenland-shark lifetime [S5]. The Northwest Atlantic Fisheries Organization only prohibited retention in international waters in September 2022, and post-release mortality from bottom trawls is unmeasured [S5].

The replacement arithmetic is unforgiving. If your first reproduction is at age 150 and the average individual is hauled up well before then, your contribution to the next generation is zero. The species evolved its biology for a world in which 400 years was a survivable timescale. Industrial fishing operates on a timescale of weeks.

The 502-centimetre female whose lens was carbon-dated to 392 years was born somewhere around 1620, give or take a century in either direction [S1]. Bach was not yet born; Newton was about to be. Some shark of that cohort, somewhere under the ice right now, is older than every nation along its migration route — and on present trends, may outlive the conditions its species needs to grow up at all.