The Ottawa River may currently be the best place in Canada to observe the Hickorynut, Obovaria olivaria, a freshwater mussel recently listed as an endangered species. I came to this conclusion based on dives I made starting in the late summer, in a specific area of this river.
In August and September of this year, my team and I picked up on research conducted one year back on the distribution and abundance of Hickorynut populations in the Ottawa River.
We knew from the start that the Hickorynut’s preferred habitat differs from that of other freshwater mussels. This mussel prefers settling in deep areas of major rivers (over 3 m in depth), in strong currents far from riverbanks, and on sandy bottoms.
This time round, however, in addition to accounting for the species’ habitat preferences, we decided to focus our efforts on areas where sturgeons, its host fish, were most abundant in the river.
Lake sturgeons (Acipenser fulvescens) are known to play a major role in the reproductive cycle of the Hickorynut. Biologists believe that it is on the gills of this fish that Hickorynut embryos or larvae, also called glochidia, attach themselves to complete their development. They are then dispersed throughout the river. Lake sturgeon populations have greatly diminished in the Ottawa River, compared to their historical levels. They are still present, however, especially in wild, free-flowing reaches, far from the influence of dams.
To spot the best sturgeon habitats in the Ottawa River, we consulted researcher Tim Haxton’s doctoral thesis as well as an article he jointly published with Scott Findlay. Then, we matched this information with data on the Hickorynut’s preferred habitat. As you will discover further on, this strategy for determining diving sites paid off well beyond our expectations!
During the month of September, we made several dives in an area of the river that was still relatively free-flowing and wild, far from big cities and hydro-electric power stations. We targeted the Finlay Islands area, near the village of Waltham, slightly upstream from Fort-Coulonge, Quebec. This part of the Ottawa River is called “Coulonge Lake”. The Finlay Islands make up a unique ecological reserve in Quebec.
To conduct this fieldwork, I was assisted by other divers, Nancy, Andy, Mark and Tanya, as well as my research assistant Jacquie. Vince, a local resident familiar with navigating in this sector, also helped us out by scouting the area before the dives.
The Finlay Islands area matched all the criteria needed to find Hickorynuts: a long reach where the river is wide, with a medium depth (3 to 6 m) across nearly the entire width. The current is strong, and there is no dam nearby. The bottom is sandy and, above all, the data confirm the presence of an abundant sturgeon population in the area.
Right from the first dives, we hit the jackpot! Indeed, diving to a depth of about 4 meters, far from the island banks and staying well within the current (5 to 10 cm/sec), we were very surprised to come upon a vast population of Hickorynuts in this wide stretch of the river! We used a 1 m2 (1 m x 1 m) quadrat to estimate the average density of this population at 0.8 individuals per square meter, which is high for a rare species.
In fact, our data suggest that in the area south of the Finlay Islands, Hickorynuts often made up over 25% of all mussels found in our quadrats. I had never seen this before! These are very encouraging results for this rare species.
Thanks to other dives around the Finlay Islands, we were able to determine that this Hickorynut population is widely distributed, possibly covering the equivalent of many square kilometres of sandy habitat on the river bottom. We estimate that there are tens (if not hundreds) of thousands of individuals in this area!
Of course, the entire area includes other much more common species of freshwater mussels that are not endangered and can be found in great numbers on the river bottom.
I don’t think it’s a coincidence if “Coulonge Lake” has such great numbers of Hickorynuts—on the contrary. Let’s look at the facts: the reach just further upstream, called “Allumettes Lake” (going towards Pembroke and Petawawa), as well as the reach further downstream, northwest of Grand Calumet Island, are part of a long reach of the Ottawa River that is still relatively wild.
All along this reach, which spans over 70 km, the river flows freely without encountering any dams. It includes several great rapids that are ideal spawning grounds for several fish species, including the sturgeon. Indeed, it is in this large area that sturgeon populations are at their highest numbers in the Ottawa River—in short, an area hardly impacted by humans that includes a rich aquatic biodiversity. This is truly a haven for the Hickorynut and a natural heritage that must be preserved!
Stay tuned for other findings from our fieldwork on freshwater mussels in Canada, including those in the Ottawa River.
Translated from French.