Before starting a large-scale tagging study, it was necessary to show that fish could survive this invasive procedure. I started working on the project in the summer of 2018, right as I came out of my undergrad. As the first fish began running up-river, I scrambled to get all of the necessary equipment ready and set up my research station.
Tagging trials took place at the White Rock fish ladder, which diverts fish around one of NSP's generating station that blocks off the river. The ladder functions as a pool and weir design: fish work their way up by jumping from one pool to the next. There are also resting pools as well, "because it's a long journey for some of the fish" (Terry Toner). As fish exit the ladder, researchers from DFO and the Acadia Centre for Estuarine Research (ACER) are able to count them using video recordings, which provides an estimate of the year's spawning biomass.
Of course, I did not get to the tagging right away - like with human surgeries, animals need to be anesthetized before we can do any work on them, and because every species is physiologically different I first needed to figure out what concentration of anesthetic would work best for my fish. When it comes to fish surgeries, there are many anesthetic options available, including CO2, clove oil and Benzocaine. However, the only method currently approved by the Canadian Council on Animal Care is a chemical called tricaine methanesulfonate (TMS), which is what I will be using for my study. TMS comes as a white crystalline powder that is easily dissolved in water, and can be buffered with household baking soda. There are also some important considerations in regards to administering the anesthetic - with help from DFO scientist Dr. Hardie, I was able to set up a continuous flow-through anesthetic apparatus, designed to wash TMS water over the fish's gills during the surgery process. This keeps the fish sedated, prevents their skin from drying out, and provides oxygen, giving me more time to do my job carefully.
The tags I'll be using for my study are a new development by the acoustic tagging company VEMCO Ltd, called V5-HR tags. V5 refers to the size of tag, while HR is the type of signal the tags emit. Traditional acoustic tags emit an 8-pulse signal at either 69 or 180 kHz frequency, with the time intervals between pulses encoding the tag's unique ID. While really useful in some environments, the long duration of the signal (several seconds) can be problematic in areas like the Bay of Fundy, where current speeds are often faster than the receiver's ability to detect and decode a tag. The HR signal, in contrast, is made up of just one-pulse, increasing the likelihood of detection. Another advantage of these tags is that they are significantly smaller than older versions, which decreases the load on the fish. After tagging, fish were held for up to three days to monitor for behavioral signs of distress .
For these early trials, I used non-transmitting (dummy) models of the HR tags, which replicate the size and weight of real ones but don't have a battery. The results so far are very promising! I observed high survival and fast recovery rates in all tagged fish, with no cases of tag loss (Tsitrin, unpublished data). Within minutes after the surgeries, the fish would recover from anesthesia and regain normal swimming ability (i.e. not visibly different from non-treated fish). After three days, fish were euthanized and dissected in order to ensure no internal damage was caused by the tagging process. This is really exciting news, as small pelagic forage fishes are rarely tracked using acoustics, so this technology opens up numerous new research opportunities. A few more things need to get done before I begin the tracking study, which is set to start mid-May, as the Gaspereau begin the seaward migration. This study is only a first step, but holds a lot of potential for the understanding and management of the species.
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AuthorLiza is a marine biologist, artist and photographer with a passion for ocean conservation. Archives |