Tarpon is one of the most iconic and prized salt-water fish in the Southeastern and Gulf states of the U.S.
Known to anglers as the "Silver King," these fish can grow up to 200 pounds and fight fiercely, often leaping out of the water in their efforts to shake a hook.
But despite their legendary toughness, tarpons are also vulnerable to various threats, such as fishing, habitat loss, and degraded water quality.
To better understand and conserve these fish, researchers from the University of Massachusetts Amherst have used a novel technique to track their movements and behavior over five years.
Tarpon Biology: An Ancient and Unique Fish
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Tarpons belong to an ancient genus of fish that dates back to the Cretaceous period, about 113 million years ago.
They are among the most primitive species classified under 30 orders of bony fish. They have several unique features that make them adaptable to various environments.
For example, they have a modified swim bladder that allows them to gulp air from the surface when oxygen levels are low in the water.
This ability enables them to survive in hypoxic or anoxic conditions, such as mangrove lagoons or rivers with dams.
Tarpons are also thermophilic, meaning they prefer warm water temperatures between 72 and 82 degrees Fahrenheit.
They can tolerate salinity changes from fresh to salt water, but they tend to avoid cold water2. Tarpons are carnivorous predators that feed on fish and large invertebrates2. They have large mouths with protruding lower jaws that can engulf their prey whole2.
Acoustic Telemetry: A High-Tech Tool for Fish Tracking
The researchers, led by Lucas Griffin, a postdoctoral researcher in environmental conservation, and Andy Danylchuk, a professor of fish conservation, used acoustic telemetry to monitor the migration patterns of 200 tarpons across thousands of kilometers.
Acoustic telemetry involves two devices: a small acoustic transmitter, surgically implanted in the fish, and an acoustic receiver, anchored in place for years at a time.
Every time a tagged fish swims within the detection range of a receiver, the receiver records the date, time, and ID of that specific fish.
Acoustic telemetry has several advantages over other methods of fish tracking, such as satellite tags. The transmitters are small and do not hinder the fish's movement, they work continuously for at least five years and they cannot be lost.
The receivers are also part of a larger network of acoustic arrays that span the entire coastlines of the U.S., Canada, and the Caribbean, allowing researchers to track fish movements across vast distances.
Danylchuk explained that acoustic telemetry was the only way to get such a detailed understanding of where and when tarpon were migrating, and over so many years.
Two Distinct Subgroups of Tarpon: Implications for Conservation
The researchers analyzed the data from the acoustic telemetry network and found that there are two distinct subgroups of tarpon: one that migrates along the Atlantic coast from Florida to North Carolina, and another that migrates along the Gulf coast from Florida to Texas.
These subgroups have different timing and spatial extent of migration, as well as different exposure to environmental conditions and human impacts.
The researchers also found that tarpon uses both coastal and estuarine habitats during their migration and that they exhibit high site fidelity, meaning they return to the same locations year after year.
These findings have important implications for the conservation and management of tarpon, as they suggest that different subgroups may require different strategies to protect their habitats and reduce their threats.
Griffin said that every fish told a story and that by using acoustic telemetry, they could listen to those stories and learn more about how to conserve these amazing fish.
