A small female shark returned to the same Hawaiian waters five times across three years. Researchers recognized her not by a tag or tracking device, but by her face—or rather, the distinctive white pattern splashed across her dorsal fin. And something else: a deformity in her snout, origin unknown.

She had no fishing gear trailing behind her. No signs of pregnancy or mating. Just that bent rostrum and a pattern of persistence.

This individual, given the identifier s228, became one of 383 oceanic whitetip sharks photographed off Hawaii between 2006 and 2024. The resulting dataset—assembled from fishers, tourism operators, and divers willing to share their smartphone images—tells a story about a species in serious trouble and a location that may be keeping it alive.

Witnesses with Cameras

The oceanic whitetip once dominated tropical seas worldwide. Historical accounts describe them as among the most abundant sharks in the open ocean. That abundance is gone. Global populations have collapsed by an estimated 98 percent since the 1950s, driven primarily by industrial fishing. In 2018, the United States listed the species as threatened under the Endangered Species Act.

Despite international protections, massive gaps remain in understanding where these sharks go, how they reproduce, and which places matter most to their survival.

Enter the Hawaii Community Tagging Program. Launched in 2016, the program recruited the very people who encountered oceanic whitetips most frequently: small-boat fishers working around fish-aggregating devices, or FADs, off the island of Hawaii. Tourism operators running shark-watching trips joined in. So did spearfishers and recreational divers. The ask was simple—photograph any oceanic whitetip you see, note the date and location, and send it in.

The species made this possible. Each shark carries a unique pattern of white markings on its dorsal fin, as individual as a fingerprint. By comparing left-side dorsal images across thousands of submissions, researchers could track individuals without ever touching them.

Over 18 years, that citizen science effort produced a dataset unlike any previously assembled for this species in the central Pacific.

A Female-Dominated Hotspot

The numbers skewed heavily female. Out of 383 identified individuals, 241 were female and only 108 male—a ratio of roughly 2:1. Among sharks, sex ratios this lopsided often point toward reproductive significance. The waters might serve as mating grounds, nurseries, or both.

Timing added weight to that hypothesis. Encounters peaked during spring, specifically March through May, when the highest proportion of females appeared. Many bore visible mating scars—bite marks around the gills and pectoral fins left by males during copulation. Others had distended abdomens suggesting pregnancy.

Mating scars appeared most frequently in January and April. Distended abdomens peaked in late winter and spring. Then came the hard evidence: in February 2022, a pregnant female washed ashore on Kauai carrying nine near-full-term pups. In August 2020, a neonate—a newborn shark measuring 77 centimeters—was caught at Cross Seamount with an umbilical scar only partially healed, suggesting birth had occurred days, not weeks, earlier.

Taken together, these observations suggest that winter and spring represent reproductively critical periods for oceanic whitetips around Hawaii. The waters may function as a gathering place for mating and possibly for giving birth, though the exact timing remains difficult to pin down. Pacific oceanic whitetips appear to have flexible reproductive schedules rather than rigid breeding seasons.

Return Visitors

Forty-two sharks were photographed more than once. Ten appeared at least three times. The record holder—that female with the bent snout—showed up six times over three years, always off the west coast of Hawaii Island, always near Kailua-Kona.

Nearly all re-sightings occurred in this same region. One exception: a single shark photographed off the island's eastern shore. Otherwise, the pattern held. These animals were not wandering randomly. They were coming back.

The longest documented re-sighting spanned five years. A female first photographed in January 2019 reappeared in April 2024, her dorsal pattern unchanged.

Site fidelity of this degree is notable for a species capable of crossing ocean basins. Satellite tagging studies elsewhere have recorded oceanic whitetips traveling over 12,000 kilometers before returning to their original tagging location. Around Hawaii, unpublished telemetry data shows similar long-distance movements—sharks spending months in the open Pacific before their tags detach almost exactly where they were first deployed, off the western coast of Hawaii Island.

Why return? Oceanographic features around the main Hawaiian Islands include seamounts, steep underwater slopes, and deep canyons that attract migratory species. The area may offer exceptional foraging after long periods at sea. It may provide thermal refuge or reproductive opportunities. Whatever the draw, the combination of high re-sighting rates and confirmed reproductive activity suggests this region holds biological importance for central Pacific oceanic whitetips.

The Fishing Problem

More than one-quarter of the sharks carried evidence of prior fishing encounters. Hooks embedded in jaws. Trailing line, sometimes exceeding the animal's body length. Scars from hook removal. Broken jaws. Bullet wounds.

Sixteen individuals bore what researchers classified as "deterrence injuries"—deliberate harm inflicted by fishers attempting to drive sharks away from their catch. Eleven had bullet holes. Five were "jugged," a practice where a floating bottle or jug is tied to the shark to exhaust it or mark it for later killing.

The gear told stories. Circle hooks were most common, consistent with both commercial longline fisheries and smaller-scale recreational operations. Three sharks carried wire leaders and weighted swivels—gear configurations matching those used by the U.S. Hawaii deep-set longline fleet before wire leaders were banned in 2023. One of these sharks was photographed in May 2023, suggesting either noncompliance with the new regulation or that gear can remain attached for over a year.

Most fishing interactions, however, appeared to involve Hawaii's small-boat fishery—vessels under 40 feet operating within 20 miles of shore, often around FADs. This fishery is lightly regulated and has no requirement to report shark interactions. As a result, its impact on oceanic whitetip populations has been essentially invisible.

The photo-ID data provides a first look. Roughly 47 percent of sharks were observed within visible range of a FAD. Many carried multiple hooks, indicating repeated encounters.

FADs are anchored buoys designed to attract commercially valuable fish like tuna and mahi-mahi. They work. They also concentrate predators, including oceanic whitetips, which are known to feed on hooked fish—a behavior called depredation. Fishers lose catch. Sharks get hooked, shot, or deliberately injured. The cycle repeats.

Some sharks in the dataset had clearly been through this cycle many times and kept coming back. One female photographed repeatedly between 2022 and 2024 had both her dorsal fin and the lower lobe of her tail removed—finned, likely illegally—yet survived and continued to appear off Kailua-Kona in varying body condition.

Her survival was striking. So was her persistence.

Hidden Associations

Nearly one in five sharks was photographed in association with marine mammals, most often short-finned pilot whales. The relationship likely benefits the shark. Pilot whales are exceptionally skilled at locating squid, a prey item also consumed by oceanic whitetips. Whales share food within their pods, and sharks trailing behind can capitalize on scraps.

Two sharks were observed with whale sharks. Others appeared near dolphins.

These associations hint at a broader ecological picture—oceanic whitetips as opportunistic foragers, reading the ocean for cues about where food concentrates, whether around marine mammals, FADs, or underwater topography.

What Protection Means Here

Avoidance remains the most effective way to reduce fishing mortality for threatened sharks. But around Hawaii's west coast, avoidance is complicated. Fishers target the same waters and often the same structures—FADs, seamounts—that attract oceanic whitetips. Both are following prey.

In 2021, Hawaii passed legislation prohibiting the intentional capture or killing of sharks in state waters. Exceptions exist for incidental catch. Enforcement is difficult. Bullet wounds photographed in 2022 and 2023 suggest compliance is incomplete.

Better handling practices could help. Regulations now require or recommend that fishers cut trailing gear as close to the hook as possible before release. The data shows many sharks still carry significant lengths of line, along with hooks, weights, and leaders. Whether this reflects noncompliance, lack of awareness, or the difficulty of safely handling a large, aggressive shark in rough conditions is unclear.

Future efforts might focus on deterrent technologies—devices that discourage sharks from approaching fishing gear without injuring them. Spatial management could also play a role, though any attempt to separate fishers from sharks would need to account for the seasonal importance of these waters to reproductively active females.

Outreach may be equally critical. Many fishers participating in the photo-ID program have shifted from viewing oceanic whitetips purely as nuisances to recognizing their conservation status. That shift, multiplied across the small-boat fleet, could reduce harm.

A Baseline, Not an Endpoint

This study establishes what was previously unmeasured: population demographics, reproductive timing, site fidelity, and fishery interaction rates for oceanic whitetip sharks around the main Hawaiian Islands. The data come with caveats. Size estimates were visual and coarse. Sampling effort concentrated heavily around Kailua-Kona because encounters there are frequent. Abundance estimates were not attempted.

But the dataset accomplishes something rare. It documents a population of a globally threatened species using a method—photo identification—that requires no capture, no tagging, and no specialized equipment. The images came from people already on the water, doing what they were already doing.

Forty-two re-sighted individuals suggest that the west side of Hawaii Island functions as a hub for central Pacific oceanic whitetips, particularly during winter and spring when reproductive activity peaks.

High fishery interaction rates suggest that hub is also a hazard.

The species has declined 98 percent globally. Recovery depends on identifying and protecting the places that matter most to the animals that remain. This study argues that Hawaiian waters, especially around the island of Hawaii, are one of those places.

What happens next will determine whether those returning sharks—including the small female with the bent snout—continue to find what they need there.

Credit & Disclaimer: This article is a popular science summary written to make peer-reviewed research accessible to a broad audience. All scientific facts, findings, and conclusions presented here are drawn directly and accurately from the original research paper. Readers are strongly encouraged to consult the full research article for complete data, methodologies, and scientific detail. The article can be accessed through https://doi.org/10.3354/meps14835