Have you ever wondered how far a lake sturgeon travels in a year? Where lake trout spend their winters? Or where lake whitefish go to spawn? If you have, you are not alone. Researchers across the Great Lakes basin have been asking similar questions for decades. More recently, they have had the help of some sophisticated technology to answer those questions. This month, we examine the wonders of acoustic telemetry and how this technology has opened up a world of opportunity when it comes to research on fish movement and behaviour.
Before acoustic telemetry, the main source of information on fish movements in the Great Lakes came from comparing the recapture location of a tagged fish to the location where it was initially released. For example, a fish captured in Lake Erie is marked by researchers with a tag, then released in that same location. Months or years later, that same fish is captured by a recreational angler in Lake Huron. The angler calls the phone number on the tag and provides the researchers with information about the fish, including the unique identifying number on the tag. This provides the researchers with information about the fish’s movements (e.g., it started in Lake Erie and ended up in Lake Huron some time later). While this is fantastic information to have, unfortunately it does not say anything about what the fish did between release and recapture. Enter acoustic telemetry!
Fish Tags
The simplest, most commonly used freshwater fish tags are often referred to as “spaghetti” tags. While their specific designs vary by brand, the basic premise is the same. The tag is made of a piece of tough plastic with one end designed to be inserted below the dorsal fin of the fish and the other end remaining outside of the fish with information printed on it. The printed information is what helps researchers gain information from recaptured fish. Typical information printed on a tag includes a contact phone number, a unique identifier code for that fish, and the name of the ministry or organization that did the tagging.
Example of fish tag inserted in a walleye (MNRF) 
Example of a fish tag inserted in a walleye (A/OFRC)
Caught a fish with a tag? Great! You get to play a part in exciting research. Take down the phone number, unique fish code, and colour of the tag and make note of your location (GPS coordinates are ideal). Do not remove the tag. Certain studies may benefit from having additional information so if it is possible to do so without harming the fish, you may wish to take photos, weigh the fish, and measure its length. Be sure to call in the information when you return to shore. The more times a tagged fish is released and recaptured, the more researchers can learn about it. However, if you decide to keep the fish (and it is legal to do so), still report the information and hang on to the tag. Some researchers ask for tags to be returned, especially those with more sophisticated technology.
Acoustic telemetry and its use in research
As we briefly described in last month’s post on lake sturgeon research, acoustic telemetry involves transmitters, or tags, and receivers. Transmitters are electronic tags that broadcast a series of sound pulses (or pings) into the surrounding water. These tags are either surgically implanted in a fish, or externally attached. Acoustic tags vary in size depending on the species they are intended for and the required battery life. Receivers are small, data-logging computers anchored near the bottom of a lake or river that ‘listen’ for tagged fish, when a signal is identified, the tag’s unique ID code is saved with the date and time. The transmitter usually transmits a signal once every minute or two and can be heard by the receiver anywhere from a few meters to a few kilometers away, depending on bathymetry and other factors. More advanced transmitters incorporate sensors that can also provide information about pressure (to determine depth), temperature, and acceleration (to determine swimming behaviour).
Receiver anchored on lakebed (GLATOS) Tag inserted in a round goby (GLATOS) 
Tag inserted in an adult walleye (GLATOS)
When the data are downloaded from the receiver, researchers can determine when and what fish were detected by the receiver. More receivers mean more data and a better idea of how exactly a fish got from one area to another and how long it took. As a result, receivers are often placed together in ‘arrays’ to provide more details about the movements of fish.
DID YOU KNOW?
Sound travels four times faster in water than in air!Fish Tracking Using Arrays
An array is a series of receivers placed so that their detection ranges overlap. This could take the form of receivers spaced out in a line across an entire body of water (or section of it) to more confidently determine presence or absence of fish. Alternatively, this could be a positional array with receivers located close to one another in order to triangulate a fish’s position more precisely.
White circles denote acoustic receivers. Several extensive arrays maintained by Great Lakes Acoustic Telemetry Observation System projects span Lake Erie (Faust et al., 2018). 
Positional arrays use the difference in time it takes for a signal to be “heard” by three or more receivers in order to triangulate the position and track (movement direction) of a fish (GLATOS).
Great Lakes Acoustic Telemetry Observation System (GLATOS)
Acoustic telemetry is limited by the presence of receivers. Not only does it require some existing knowledge of the movement range of the tagged species, it also requires an effective array of receivers in that area to obtain detailed information. You can tag a fish, but if it does not pass by a receiver, it will go undetected. Fortunately, as acoustic telemetry increases in the Great Lakes and as the cost of the technology comes down, more arrays will be deployed to fill in the gaps.
The Great Lakes Acoustic Telemetry Observation System (GLATOS) was established by the Great Lakes Fishery Commission in 2010. GLATOS is a binational network of researchers who work collaboratively using acoustic telemetry to: (1) understand fish behaviour in relation to Great Lakes ecology; and (2) provide information useful to fish managers in their decision making.
The GLATOS network helps connect acoustic telemetry researchers and their projects, and assists in the sharing of equipment and data within the Great Lakes basin. Researchers in the network can access data from their tagged fish that are detected anywhere within the GLATOS system of receivers deployed throughout the Great Lakes basin. This creates an opportunity to address geographically broad research questions that would not otherwise be possible for a single project. For examples of the types of studies researchers in the GLATOS network are undertaking, visit: https://glatos.glos.us/projects.
At present, Georgian Bay represents a significant gap in the GLATOS system of receivers. Aside from several receivers placed between the Bruce Peninsula and Manitoulin Island, there are currently no receivers in Georgian Bay. It is possible, however, that researchers are undertaking acoustic telemetry studies on an individual basis, rather than connecting with, and capitalizing on, the larger GLATOS network. If there are the resources, there will likely be receivers established here in the future to answer questions about a variety of species.
TAG, you’re it!
While acoustic telemetry may be the cool new technology in the Great Lakes, the good old-fashioned “spaghetti” tags are still widely used and provide extremely important information. This low-tech option is also low-cost and can still give great insights into fish movement. Take this recent Anishinabek/Ontario Fisheries Resource Centre find for example. A walleye tagged by the A/OFRC on the Magnetawan River in spring 2019 was caught in the St. Clair River in spring 2020 – that’s a journey of almost 400km!
UPDATE: Since this story was posted in January 2021, exciting improvements have been made with regard to acoustic receiver coverage in Georgian Bay. The image below shows an updated GLATOS receiver map, current as of August 2021.
