Research and Conservation

Why Do We Tag Fish?

Fish tagging has been gaining popularity for decades, with biotelemetry now being the primary method used to study animal movements. But what is this technology, and why do we use it?

Steelhead Trout tagged with a spaghetti tag in the Russian River basin; Photo Credit: Des Colhoun

Most of what we know about animal migrations today comes from tagging programs. The practice is way older than you might think: the first recorded attempts to mark an animal occurred sometime between 218 and 201 B.C., when a Roman officer tied a note describing plans for military action to the leg of a swallow, which carried it to its nest positioned in close proximity to a military outpost in need of the information. In one of the earliest reports of tracking, dating to 1653, Isaak Walton described how individuals tied ribbons to the tails of juvenile Atlantic salmon and ultimately determined that these fish returned to their natal rivers for spawning. Since the late 1800s, numerous fish tagging experiments have been conducted, with large-scale programs taking off all over the world in an effort to study the biology and ecology of fish populations. These types of studies are generally known as mark-recapture, because it is essential that marked individuals be caught at some point after being released so that the distance travelled by that individual can be estimated. While still used today, recent advancements in technology have allowed tagging studies to move away from needing to physically re-capture animals, instead using transmitter tags to record movement.

In plain terms, transmitter tags emit some kind of signal, which can be detected by a receiver. The earliest used were radio transmitter tags, which scientists could locate using an antenna and receiver from a plane, vehicle, or on foot, or by setting up radio towers in an area of interest. Radio transmitters used to be fairly large and were only used on larger animals, but improvements in technology lead to tags becoming smaller, eventually becoming so small they could be used to tag insects, swallowed, or placed under the skin of an animal! The development of the Global Positioning System (GPS) in the 20th century opened up a new era of animal tracking using satellites. Satellite tracking is similar to VHF radio tracking, but instead of radio waves the tag sends signals to a network of satellites, allowing scientists to get positioning data and track the animal remotely using a computer. Satellite networks have tracked the migration of caribou, sea turtles, whales, great white sharks, seals, elephants, tunas and countless other species, and have quickly become a popular (albeit expensive) technology to use. GPS tracking is the newest, shiny player in the field of wildlife tracking; in GPS tracking, a receiver, not a transmitter, is placed on the animal, which picks up signals from satellites to calculate its location and map the movement of the animal. The data gathered by the receiver is then sent to another set of satellites, which in turn sends the data to the scientist’s computer. This method is popular for both terrestrial and aquatic species, and there are now GPS receivers that are solar powered and small enough to attach to songbirds!

But when in comes to tracking fish in the ocean, GPS and satellite tracking are not always viable. Instead, scientist often use smaller passive integrated transponders (PIT tags), or acoustic telemetry. PIT tags are the smallest and cheapest of tags available, consisting of an integrated circuit chip, capacitor, and antenna coil encased in glass. They are called passive transponders as they do not have an internal battery and therefore cannot emit their own signal. Instead, PITs are activated when a fish swims past an array of scanning devices that generate a close-range electromagnetic field. The tag is briefly activated and sends back a unique alpha-numeric code, which serves as a lifetime barcode for an individual animal. This technology is useful in enclosed watershed and narrow rivers, but cannot track large-scale oceanic movement. This is where acoustic tags come in – acoustic transmitters are attached to animals, generally via internal implantation, and programmed to send a unique signal that can be detected by acoustic receivers. The signal encodes a unique ID for the tag, and a careful placement of receivers can provide accurate positioning in space and time! These tags are more useful for large-scale movement studies, but are limited by size (the smaller the animal the shorter the tag’s battery life), as well as the positioning of receivers, which have a limited detection range that also changes with environmental conditions.

Acoustically tagged tiger shark passes one of OTN’s bottom-moored acoustic receivers; Photo by Jim Abernethy

Every year, hundreds of researchers around the world tag and release thousands of fish – everything from Bass to Great White sharks! We’ve seen species travel farther and faster than we ever thought possible. We can even look at fine-scale movement, behaviour, and interactions with predators or prey. Today, tracking is used to monitor and manage many commercial fish populations. On a larger scale, tracking can be used to map-out where certain species travel throughout the year, how they interact with people and man-made structures, improve fisheries, study the impacts of climate change on species distributions, and so much more!

For my own research, I will be using acoustic tags to monitor the movements of Alewife (locally known as Gaspereau or Sawbellies) through the Gaspereau River and Minas Basin. The Gaspereau Tagging Project will be part of an ongoing, multi-species research project done at the Coastal Ecology Lab at Acadia University and funded by the Offshore Energy Research Association of Nova Scotia to investigate movements of migratory fish species, particularly in an area of tidal turbine development in Minas Passage.

Cape Sharp Tidal wast the first of 5 patent-holders to test turbines in Minas Passage, with the potential to generate 2.5 GW of energy. Photo Credit: Marc Semail, VEVC

In-stream turbines are free-standing, underwater turbines that generate electricity from moving currents, i.e. without the need for additional infrastructure like barrage or dams to force water flow. The Bay of Fundy is an important potential source for tidal power development in Canada, due to its large tidal amplitudes and fast current speeds that generate a lot of energy. In 2009, the Fundy Ocean Research Centre for Energy (FORCE) establishes a designated site for the demonstration and testing of industrial-scale, in-stream tidal energy devices in Minas Passage – a narrow channel that connect Minas Basin to the larger Bay of Fundy. Although the FORCE site represents a small area of the Minas Passage (<20% of the passage width), there is a concern that these turbines might affect the numerous species of fish that move into Minas Basin every summer for feeding and spawning, such as Atlantic Sturgeon, Striped Bass, American shad, etc. These seasonal migrants occur in large numbers during summer/fall, and many support important commercial fisheries in the area, as well as providing a food source for marine mammals such as seals, porpoises, and small whales. It’s been shown in the past that turbine blades can be damaging to fish, causing injury or even death, however most previous studies have looked at river dams, which are very different from in-stream turbines. We want to know whether species could be affected by the types of turbines being tested at FORCE. This question can be examined on several levels: a) do fish move through areas where turbines are present?, b) do fish actually pass through the turbine blades, or are they able to avoid them?, and c) does interaction with turbine blades result in serious injury or death? 

The Offshore Energy Research Association (OERA) of Nova Scotia has provided funding for several projects run by Dr. Mike Stokesbury’s Coastal Ecology Lab at Acadia University, with the common goal of addressing that first question: do fish commonly use the area in Minas Passage where tidal turbines are being tested?  Studied species include Atlantic Sturgeon, Striped Bass, American Eel, Tomcod and, of course, the Gaspereau (read all about it at the CEL website 

My species of interest is the Alewife (Alosa pseudoharengus): an anadromous forage fish in the family Clupeidae, that is widely distributed along the Atlantic coast of North America, from the Gulf of St. Lawrence to North Carolina. During spawning runs, Alewives are the dominant species in many rivers of Maritime Canada, and support lucrative commercial fisheries throughout the region. Fisheries target adult Alewife as they migrate upstream through the estuary and river, and those fish that make it past the nets proceed upstream to spawn in the Gaspereau Lake.

White Rock fish ladder

To get there, fish must first pass by two hydroelectric dams at White Rock and Lanes Mills, where fish ladders have been set up to facilitate passage (the effectiveness of these passages is another topic of great interest to our lab, and future research is looking at addressing this question). To investigate where fish go after they’ve spawned, they will be fitted with newly developed HR acoustic tags during their seaward migration. Receivers scattered around Minas Basin and the FORCE site will allow me to track the temporal (seasonal and diel) movements of tagged fishes within Minas Passage, and quantify residency at the FORCE test site to assess the potential risks of fish-turbine interactions.


Marine biologist, nature enthusiast, and artist on a mission to promote ocean education and conservation 🌊

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