WHITE SHARKS IN CANADA
Following the seasonal journeys of the North Atlantic’s most iconic predator.PART 3Following the Migration
How scientists follow a white shark across an ocean
A shark disappears beneath the surface. From the boat, the ocean closes behind it almost immediately. No wake remains. No path is visible. Yet months later, a receiver on the seafloor may record its identity, a satellite may receive a position, or a photograph may prove that the same animal has returned.
Scientists do not follow a white shark across the Atlantic by watching it continuously. They assemble a journey from signals—each technology recording a different part of the animal’s life, each with its own blind spots.
A coded sound becomes evidence of presence.
An acoustic transmitter gives an individual shark a coded identity. When the shark swims within range of a compatible underwater receiver, the station records the tag number, date, and time. The receiver does not continuously map the shark. It documents a confirmed encounter at one place.
One detection can establish presence. Repeated detections can reveal arrival, departure, local residency, route choice, and return in a later year. Networks matter because a shark tagged in one country can be heard by receivers operated by partners elsewhere.
Canada’s Ocean Tracking Network has deployed acoustic infrastructure since 2008. Its Northwest Atlantic arrays collect movement and habitat-use data from tagged sharks and many other marine animals. The result is less like a live video and more like a constellation: scattered points that become meaningful when connected across time.
SHARK
RECEIVER
Identity + date + time + receiver location
Some tags describe the water the shark moved through.
Satellite-linked tags answer questions that fixed receivers cannot. Position-reporting tags can transmit when an antenna breaks the surface. Pop-up satellite archival tags record measurements such as depth, temperature, and light over a programmed interval, then detach, float upward, and transmit summarized data.
These records reveal the three-dimensional migration: not only where a shark travelled, but how it used the water column. In a western North Atlantic study, tagged white sharks used depths from the surface to 872 metres and experienced temperatures from −0.9°C to 30.5°C across residency and migration phases.
That range is a reminder that a line drawn on a map is only the horizontal shadow of the journey. The shark is also moving vertically—sometimes through hundreds of metres of ocean.
TAG
A photograph can be a mark–recapture record.
White sharks carry visible individuality: the shape and trailing edge of the dorsal fin, scars, pigmentation, and other markings can distinguish one animal from another. When researchers match a new photograph to an existing catalogue, they document that individual without needing a new tag.
Photo-identification can reveal survival, return, site fidelity, growth, and movement between photographed areas. The Atlantic White Shark Conservancy and Massachusetts Division of Marine Fisheries maintain a Northwest Atlantic catalogue containing hundreds of tagged and untagged individuals, expanded through collaboration along the coast from Florida to Nova Scotia.
This method depends on image quality, angle, and search effort. A shark that is not photographed has not necessarily left. Absence of evidence is not evidence of absence.
- Dorsal-fin profile
- Pigmentation
- Scars and injuries
- Body proportions
MATCH → INDIVIDUAL HISTORY
Every track contains gaps—and every method contains bias.
An acoustic tag is silent to the dataset when the shark is outside receiver range. A satellite tag may fail to report, detach early, or provide estimated rather than exact positions. A photographed shark may be misidentified or never photographed again. Tagging locations can also bias the sample toward animals already using a well-studied hotspot.
The 2022 Canadian analysis combined a decade of collaborative acoustic and satellite data. Its authors were explicit about representativeness: most tags had been deployed off Cape Cod, and sharks connected to that aggregation might not represent the whole Northwest Atlantic population.
Good science does not hide these limitations. It measures them, reports them, and avoids making a confident migration map out of incomplete points.
The migration emerges when methods overlap.
Acoustic detections provide precise encounters. Satellite tags reveal broad movement and vertical behaviour. Photo-identification extends individual histories beyond tag life. Fisheries records, sightings, environmental data, genetics, and field observations add further context.
Together, these methods show seasonal northward movement, concentrated use of continental-shelf habitat, individual variation, and return. They also reveal what remains unknown: how many sharks use Canada, which habitats matter most, how movement changes with age and sex, and what happens between detections.
Following a white shark across an ocean is therefore not a matter of watching one bright dot move across a screen. It is the patient reconstruction of a life from evidence collected by many people, instruments, and institutions—often across borders and over many years.