Freshwater mussels 101: Explaining the “aquatic archaeology” behind mussel relocation
June 03, 2022
Want to adhere to regulations but don’t know much about freshwater mussels? An aquatic biologist dives into the details of surveys and relocations.
The sun hits your back as you dip your trowel into the water. All around you, a team of researchers in wet suits wades through the water, searching for mussels to identify, measure, tag, and relocate. From afar, the whole operation looks like an underwater archaeology dig.
Ah, field work. I’ve always enjoyed working outdoors. As an aquatic biologist with extensive marine and freshwater experience, I’ve spent years studying mussels, and I’ve been involved with numerous projects involving native freshwater mussel species at risk in my home province of Ontario, Canada.
Does your project require a survey or relocation program for freshwater mussels? They are a protected species. If you don’t adhere to federal or provincial regulations, you could face project delays, fines, or even jail time.
If you can’t properly identify a common mussel from a mussel species at risk, you run the risk of contravening federal and provincial species at risk regulations.
If you’re new to the idea of a mussel salvage program, I’ll explain what it’s all about. I’m familiar with both provincial and federal approvals processes for surveys and moves related to mussels. When it comes to these wonderful little organisms, there are a few important things to know.
What are freshwater mussels, and what do they do?
If you know anything about mussels in general, you’re likely aware that they resemble clams and can be used as food (saltwater mussels, not freshwater, are the ones that people eat). Mussels—aka bivalve mollusks from saltwater and freshwater habitats—are comprised of a fleshy interior part and a hard double shell.
Mussels are sedentary, which means that if you don’t move them to accommodate a project, they’ll likely get crushed. Or, if you need to dewater a site before work begins, they’ll dry out.
Mussels sit in substrate under the water, drawing water through themselves, absorbing nutrients, and removing bacteria. They filter the water, improving water quality for humans, fish, and other wildlife. Generally, a large mussel population helps to maintain clean water. Mussels can also produce pearls, and they’ve been used in button making.
There are nearly 300 species of mussels in North America, with over 70% listed as endangered, threatened, or of special concern. Southern Ontario serves as a “hot spot” for at risk mussels in Canada, primarily because the region represents the northern extent of their range.
Professionals move mussels for the City of Ottawa’s Britannia Beach project. Completed under a Species at Risk Act permit, the project was one of the largest mussel relocation efforts in Canada based on area to be searched.
What projects need freshwater mussel surveys or relocations?
My team has participated in numerous mussel detection and relocation surveys to support transportation, oil and gas, water, and wastewater projects, when the project involves work in the water. Perhaps you’re planning a bridge expansion or a pipeline crossing. Maybe you need to dredge a beach. When disturbing the substrate beneath the water—where mussels could be present—you need to ensure you’re abiding by government regulations.
Any work that might disrupt or destroy habit for mussels could trigger a mussel survey or relocation. Different countries and regions have distinct regulations. In Canada, projects that involve working around water need to abide by the federal Fisheries Act as well as the Species at Risk Act, both managed by Fisheries and Oceans Canada. Provincially, in Ontario, we help clients follow the Endangered Species Act, managed by the Ministry of Environment, Conservation and Parks. You can face repercussions like fines, jail time, or project delays if you don’t adhere to these rules.
How do surveys and relocations work?
Put simply, an initial survey is a site visit by an expert that’s knowledgeable enough to know what to look for in the water. The expert may have a sense of what species might be present in an area and if the habitat is suitable for mussels. A project requires a survey if federal and provincial agencies don’t have information about a mussel population on a site or if there is an indication in their background data that mussel species at risk might be present.
The goal of a mussel relocation program is to collect and relocate all juvenile and adult mussels—including species not at risk—from a potentially impacted area. We record measurements of length, height, and width for relocated mussels.
There are nearly 300 species of mussels in North America, with over 70% listed as endangered, threatened, or of special concern.
To relocate, you need to find a similar habitat to the project site. Often, it’s a short distance upstream from the project site. Then, we demarcate our area and systematically scan for mussels. When working in clear water, you can pull out any mussels that you find (they’re often buried with a corner poking out). Often, you’ll need the help of a mussel viewer—a box with clear Lucite at the bottom—that helps you see through cloudiness as you push it down toward the bottom of the sediment. Aside from scanning, we use trowels, trays, and sieves to remove mussels and place them in a retaining bucket that keeps the mussels healthy and cool.
We tag mussels with unique numbered tags so we can return to track individuals to evaluate how well the relocation has worked. As part of a required post-relocation monitoring program, we will remeasure them after a year or two to confirm they are healthy and see if they’ve grown.
Some relocations involve a transponder glued to mussels, so you can track mussels via a radio tag. In smaller areas, you place tent pegs into a river, and use GPS to relocate the pegs and the mussels around them.
Shallow and deep techniques
Mussel relocations can happen in two ways—it all depends on the water depth. For a shallow-water survey, you can use the “raccooning” techniques I mentioned above, where you search by hand or using hand-trowels, with the help of viewing boxes and long-handled clam scoops.
When the depth of the water reaches over three feet, biological divers perform scientific diving surveys. These surveys resemble the shallow water work, except the dive team has an air supply from the surface so they can search the deeper substrate.
To relocate mussels, you need to find a similar habitat—typically, a short distance upstream from the removal site.
The importance of timing and working with the right experts
When it comes to mussel relocation, keep your eye on the calendar. In Ontario, relocations are very timing-specific. You obviously wouldn’t want to delay a project by a year because you missed the window for a relocation.
Warm water temperatures give mussels a better chance to bury themselves into substrate before the onset of winter. The lower temperature threshold for burrowing activity is 16 Celsius (60 Fahrenheit), so the window for working with mussel relocations typically runs from early June until the end of September in Ontario. Of course, temperature windows in other regions can be longer or shorter.
Aside from timing, here’s another important point: you need to make sure that you’re working with an expert that knows the biology of these organisms. To the average person, most mussels look identical. A layperson may even confuse a mussel with a rock. Mussels also need to be placed in a particular way so they can breathe. If you can’t properly identify a common mussel from a mussel species at risk, you run the risk of contravening federal and provincial species at risk regulations. The identification, measuring, tagging, and placement of mussels takes an expert with specialized training.
Aquatic archaeology
Like I said earlier, it feels like we’re performing aquatic archaeology when we’re out in the water. I’m fascinated by mussels, and I’ve handled many species throughout my career, including hickorynuts, creepers, fatmuckets, elktoes, and threehorn wartybacks. I’ve worked on some rewarding projects, including a recent relocation for a beach-dredging project that relocated over 43,000 mussels—a huge number for a single relocation in Ontario. I’m proud that my team helps our clients move projects forward while simultaneously protecting these fascinating organisms.