Taxonomy

Rarity

The sevengill is the largest shark a Southern California diver has a realistic chance of meeting, and meeting one is still an event. It reaches 10 feet, it has a blunt broad head with a mouth that looks too wide for it, and it moves slowly enough that divers who see one usually get a long look. The IUCN listed the species as Vulnerable in February 2020 with a decreasing population, and California sets one of its tightest recreational limits on it: 1 fish per person per day for sixgill and sevengill sharks each, against a general default of 10 for most species. The species has very low resilience, with an estimated minimum population doubling time over 14 years. Nothing about a shark that reaches 49 years old recovers quickly.

Seasonality

Location

Sevengills live on temperate and subtropical continental shelves around the world, everywhere except the North Atlantic and the Mediterranean, and in the eastern Pacific they run from British Columbia south to Chile. Records reach about 1,870 feet, but the sharks a diver meets are in shallow inshore water, usually above 260 feet and often far above it. They use coastal bays heavily, and in California that comes down to 2 places: San Francisco Bay and Humboldt Bay are the primary pupping and nursery grounds on this coast. Pups are born in shallow water in late spring and early summer, and newborns turn up regularly in San Francisco Bay.

They are not drifters. Acoustic tagging in San Francisco Bay detected more than half of tagged sharks in the bay through most of the year, most abundant from spring through fall, with some moving to deeper water in winter, and adults appear to return to the same bays year after year. The range they are capable of covering is far wider than that pattern suggests. Individuals tagged in San Francisco Bay have turned up in Baja California and in Willapa Bay, Washington.

The other thing worth knowing about where sevengills are is that the answer changed. Encounters at La Jolla were not commonly reported before 2007. Divers began reporting them regularly after that, enough that a photo identification project started in 2010 to try to make sense of it. Over 20 encounters were logged in the first year alone. Between 2010 and 2020 that project matched roughly 76 individual sharks in the La Jolla area by their markings. Why the sightings rose is genuinely not established, and the project exists because nobody has the answer.

Deep Dive

Sevengills are old in a way most sharks are not. Nearly every shark alive has 5 pairs of gill slits. This one has 7, and that puts it in a small family whose body plan traces back to a lineage that predates the modern shark groups. It is the only shark in the northeastern Pacific with 7 gill slits, which makes the identification trivial once a diver knows to count. The rest of the animal is broad and heavy: a wide head, a short blunt snout, a single dorsal fin set far back, and a spotted grey-brown body.

The mouth is built for a specific job and it is worth understanding, because it explains the diet. The lower teeth are comb-shaped, a row of points that grips and anchors whatever the shark has hold of. The upper teeth are jagged and cut. Together they work less like a trap than like a saw with a vice attached: the lower jaw holds, the shark rolls or thrashes, and the upper teeth take a piece out. That is a design for eating animals too large to swallow.

The diet reflects it. Sevengills eat other sharks, bat rays, harbor seals, crabs and carrion. In Humboldt and San Francisco Bays the main prey are brown smoothhound sharks and bat rays, and sevengills over about 8.5 feet commonly take harbor seals. The most striking documented behavior is that they do it together. Observers have seen sevengill sharks hunting seals in packs, which is rare enough among sharks to be worth stating plainly rather than dressing up.

Reproduction is the other extreme. A sevengill carries her pups for about 12 months and then gives birth to a litter that FishBase puts at 82 to 95, among the largest of any shark. Pups are 16 to 21 inches at birth and are on their own immediately, which is what the shallow bay nurseries are for.

The question every diver asks about a 10-foot shark deserves a direct answer, and the honest one has 2 parts. First, on unprovoked attacks: the Monterey Bay Aquarium states there is no record of a person being attacked by a sevengill in open water. FishBase is more cautious, classing the species as capable of causing injury, noting it has attacked divers in captivity and saying it may be involved in attacks off California and South Africa. Both statements can stand, because they are answering slightly different questions.

Second, and more useful to anyone carrying fish: there is a documented California incident, and it was about the fish, not the diver. On June 8, 2011, a spearfisherman working near the Children's Pool in La Jolla with 2 companions was approached by a sevengill of about 7 feet. The shark went for a calico bass on his stringer and made 3 contacts on his calf on the way. The teeth left clear gashes in his wetsuit and he was not injured. One of his companions shot at the shark, missed, and lost the spear. San Diego lifeguards did not close the beach.

That incident is the practical lesson and it is not really a shark-attack story. A shark competing for a dead fish tied to a diver's waist is doing something entirely different from a shark hunting a person, and the fix is the same one that applies to every large predator on this coast: a stringer belongs on a float line well away from the body, not on the belt. A sevengill that shows up while fish are on the line is there for the fish.

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.