Spearfishing Stats

Taxonomy

Rarity

The bigeye thresher is the second thresher shark in this Ichthyopedia and the one almost nobody can name.

The International Union for Conservation of Nature assessed it in 2018 and lists it as Vulnerable, meaning a high risk of extinction in the wild, and it sits on Appendix II of the international wildlife trade treaty. That is a step worse than the common thresher's own status when the United States Pacific stock is considered, which NOAA finds neither overfished nor subject to overfishing.

California allows 2 thresher sharks per person per day with no size limit, under a regulation that says simply "Thresher" and does not name a species. Read plainly, that covers this shark as well as the common thresher. No California source read for this entry breaks the rule down by thresher species, so a diver should assume the 2-fish limit applies and that the state does not distinguish.

Regulations

CDFW rules verified 2026-09-08

Seasonality

Edibility

Location

Bigeye threshers live in tropical and temperate seas worldwide and are highly migratory. They occur in coastal water over continental shelves, sometimes close inshore in shallow water, and on the high seas far from land. The usual band is the top 328 feet, with records down to about 2,395 feet.

That is where the honest limits of this entry sit. No California-specific occurrence, abundance or seasonality figure was found from a source read for this page. The species is circumglobal and is recorded in the eastern Pacific, and it is included here because a thresher taken or seen off southern California is not automatically the common one and a diver should know that a second species exists.

Telling them apart is straightforward once the marks are known, and there is one that settles it. A common thresher has a conspicuous white patch that extends from the belly up over the bases of the pectoral fins. On a bigeye thresher the light color of the belly does not wrap over the pectoral fin bases. Beyond that, the bigeye has very large eyes and a distinctly indented forehead, its pectoral fins are curved with broad tips rather than narrow ones, its tail tip is broad, and its first dorsal fin sits further back on the body than in any other thresher. The color above is purplish gray rather than the common thresher's brown to blue-gray.

The diet is open-ocean fish and squid: lancetfishes, herring, mackerel and small billfishes, along with bottom fish such as hake. Like the rest of its family it stuns prey with its long tail.

Spearfishing Brief

The bigeye thresher is legal in California at 2 a day under the same rule as the common thresher, and it is a rarer animal than that one.

Finding one rates a 5. This is a thinly spread, highly migratory, largely offshore shark with no established California season and no local abundance figure. An encounter is chance.

The shot rates a 3, which is lower than the common thresher's 4, and the reason is size. A bigeye thresher reaches 16 feet and 802 pounds against the common thresher's 18.8 feet and 767 pounds, and a typical adult is 11.5 feet rather than about 15. It is still a large animal requiring the bluewater rig, a big gun with a detachable point and a breakaway float line. FishBase rates the species harmless to people, the same rating the common thresher carries, and unlike the mako, blue shark, hammerhead, white shark and basking shark, which are all classed as capable of causing injury.

The tail remains the thing to respect. FishBase records that this species stuns its prey with its long caudal fin, which on a thresher is almost as long as the rest of the animal. The filmed evidence for how a thresher uses its tail comes from 2 studies, and neither one is about this species: the southern California footage is of common threshers and the widely shared Philippine footage is of pelagic threshers. What the record supports for the bigeye thresher is the plain statement that it does the same thing.

On the table it is good and the scientific record is unusually specific about how to cook it. The meat is marketed fresh and may be broiled, baked or grilled, but is described as unsuitable for steaming, boiling or frying. As with every shark, the handling matters more than the recipe: bleed the animal immediately, wash it in seawater and ice it, because the urea sharks carry in their tissue turns to ammonia after death.

Deep Dive

The name is the animal. The species name comes from Latin words meaning above and having a raised eyebrow, given for the enormous upward-looking eyes set high on the head and the marked groove that runs over them.

Those eyes are the largest of any thresher and they point up. A shark whose eyes are angled toward the surface is a shark looking at whatever is between it and the light, which is the direction prey appears from when a predator is hunting below it. The species also ranges from the surface down to about 2,395 feet, deeper than either of its relatives usually goes, and large eyes gather more light in water that has very little of it. Those 2 facts sit together comfortably. This entry does not claim the eyes evolved for deep hunting, because no source read for it makes that claim, but the anatomy and the depth range are both on the record.

The rest of the family resemblance holds. The upper lobe of the tail is very long and strap-like, almost or quite as long as the whole rest of the shark, and it is used to stun prey rather than only to swim. Reproduction follows the mackerel shark pattern: the eggs hatch inside the mother and the pups feed on unfertilized eggs she produces for them, then are born live. Litters are 2 to 4 pups and usually just 2, which is as small as any litter in this Ichthyopedia. The published figures for size at birth disagree, ranging from 2.1 to 3.5 feet in one source and 3.3 to 4.6 feet in another, but either way a newborn bigeye thresher is a substantial animal.

The reproductive detail that matters most is a negative one: there is no fixed mating or birthing season. Most sharks in this corpus breed on a calendar, and the seasonal closures and gear rules that protect them are built around that predictability. A species that breeds year-round offers management nothing to work with. Combine that with a usual litter of 2 pups, a maximum age of 20 years, and maturity at 8.3 feet, and the Vulnerable listing stops being surprising.

Where to Find Them

Beaches whose habitats match this species

Matched by habitat: a beach is listed when its biome tags overlap this species' biomes.