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There’s Something Fishy Going On...

posted Jun 7, 2016, 6:28 AM by Hector Carranco
(the author graciously  acknowledges the assistance of Connie Downes and Noel Alfonso (Canadian Museum of Nature)

It’s not just water that is sliding under your hull as you paddle up-river from the club dock. You are also paddling over lots and lots of fish. A surprising number, both in terms of abundance and diversity. 

Surprising because the stretch of river from Hogs Back to Black Rapids been changed so dramatically by people to suit our needs, not the needs of fish.  First, the river has been transformed from a fast-flowing stream to a still-water pond by the building of the Rideau Canal almost 200 years ago.  Two hundred years is not a long time in terms of ecosystem change, and the Rideau system is still adjusting to this new water regime, which favours some species more than others.  To make matters even more stressful for the fish (yes, fish feel stress), the water level, as you well know, suddenly drops every fall. Surprisingly, studies have shown that few fish are stranded by the rapidly changing water levels, and most survive the winter low water just fine. 

But the biggest change along this stretch of river has been the loss of natural shorelines. The riparian or shoreline zone is that special area where the land meets the water. Shorelines are like the lungs of the river – where water meets land, where different habitats merge, that’s where most of the life is. Baby fish (fry) and minnows shelter here among the aquatic weeds and rushes; bigger fish hunt along the natural shorelines, looking for the little fish hiding there. Aquatic insects, frogs and turtles also congregate at natural shorelines. In this stretch of river, natural shorelines begin with submerged aquatic plants like Common Water Weed, floating aquatic plants like the showy White Water Lily, or the tiny Duckweed, emergent plants, like Cattails and Arrowhead, and finally shoreline herbs and shrubs, like Willows and Dogwoods, or the beautiful Canada Anemone with its showy white flowers blooming in June. 

Common Water weed

 As people moved into homes along the river, more than half of the shoreline has been ‘hardened’ to prevent erosion. Much of the erosion is caused by the wakes from motor-boats. No one likes to see their backyard disappear into the river, so  they have dumped in rocks, concrete blocks, sheets of metal, logs treated with wood preservatives, gabions (wire cages filled with rocks), and other imaginative ways  to stabilize the shore. Land-owners have replaced the natural vegetation growing on the land just back of the water with a monoculture of grass. This is good for creating a nice unobstructed view of the river, but not so good for fish and other creatures that live in the water.  

But just like trying to sprint 1000 m with half your lung capacity, loss of natural shorelines diminishes the capacity of the river to achieve its potential for abundance and diversity of life. Half the shoreline gone; half the life gone, as a rule of thumb. 

To top all this off, the water quality is not, shall we say, pristine. There are too many nutrients in the water, mostly from agricultural fields and run-off from the city streets and storm sewers (that’s why the beach is often closed), which promotes lots of plant growth in the water - sometimes too much, which results in the mats and blobs of algae we see in the summer. The algae we see in river are single-cell ‘primitive ’plants.  The algae mats eventually die and sink to the bottom, where they decompose and use up a lot of oxygen in the water, oxygen that the fish need.  It’s all in the balance. 

Another factor working against the fish is the recent invasion of Zebra Mussels.  Zebra Mussels first appeared in the Rideau in 2000, and they have significantly changed the ecosystem.. Zebra mussels filter single-celled organisms, such as bacteria, algae, and protozoa from the water. The most noticeable result of all this filtering is clearer water. This might look good to us, but its not so good for the fish.  Before zebra mussels were here, baby fish and tiny aquatic invertebrates ate the single-celled organisms, and were in turn eaten by bigger fish. Now all this energy goes into growing zebra mussels, and almost no one eats them (mallard ducks actually do, but no fish in this section of river eats zebra mussels). That means less food for baby fish!

But the Rideau is amazingly resilient.  Scientists have collected more than 20 species of fish from this section of river. There is a healthy population of ‘game fish’ .  Smallmouth Bass are very abundant, and grow to a healthy weight of more than a kilogram. But largemouth bass, a species that is increasing rapidly in abundance in most of the Rideau, is not common here. The weedy shallows they prefer are not present in this section of river. 
 
Smallmouth bass                                                             pickerel

Another sport fish species found here is Pickerel (also called Walleye) . Pickerel are prized as the best-tasting fish in the Rideau. These mostly nocturnal feeders spawn in the fast water below Black Rapids dam.  Northern Pike up to 2 kilograms, and Muskellunge over 12 kilograms (that’s a whopper!) were also recorded here.  Muskellunge are the biggest and most ferocious predator in the river, and are the topic of the next RCC nature blog.  I haven’t seen any ‘muskies’ while paddling here, but  watch for their tails flipping up, or a duckling mysteriously  disappearing under the surface in a big swirl. They are expert ambush hunters, and often lie still in shallow water ready to pounce on their victims. 

All the ‘pan fish’ are found here – Yellow Perch, Rock Bass, Black Crappie, Pumpkinseed Sunfish and Bluegills. These are the most likely fish you will see while paddling, especially bluegills and rock bass. 

The Pumpkinseed Sunfish is the most beautiful fish you will see, with its red spot on the gill cover, and its bright orange belly. They are particularly colourful when they are spawning, in late May and June.  Watch for their circular ‘nests’ in shallow water. 
  
Pumpkinseed                          Sunfish Rock Bass                            Black Crappie

Carp are an introduced species (they are native to eastern Europe, but have been here for at least 100 years, probably released on purpose as they are considered a great delicacy by folks from Asia and Europe. ), For some reason they are not abundant in this section, although they thrive in the canal below Hogs Back – probably  the most abundant fish (by weight at  least) in the canal from Hogs Back to Ottawa Locks.  I did see one in a bathtub in the apartment buildings across from Mooney’s Bay that weighed about 12 kilograms (it's a long story. It wasn’t living there (even a big carp can’t afford to rent a bathtub)  – it was captured in Mooney’s Bay.

Fish that are less familiar are also found here – Red Horse Suckers, which can grow up to more than five kilograms – watch for them along the dock  at night and listen for the distinctive  ‘kissing’ sound they make as they suck snails from the vertical face of the dock.  Brown Bullhead (small catfish up to 30 centimetres long, also known as Barbotte (French term) or Mudpout, and Channel Catfish are also present. 

Interestingly, there are very few minnows – perhaps because of the zebra mussels. But several species of little fish (little in size and little-known to most people) were captured in one study – Killifish, Darters, Sticklebacks, and Sculpins, likely in the tributaries coming into the river. 

What lies in the future for the fish in our little section of the Rideau? The environment is constantly changing and we can only speculate. Zebra mussels are abundant today, but their time will pass – something will find them good to eat! The fish in this section are a mix of cool-water and warm-water species (eg. Pickerel and Northern Pike are cool water fish), so global warming may favour the warm-water species. There are several invasive aquatic  species looming just beyond the horizon – Asian Carp, Snakeheads (yikes – these guys are really scary!), Round Gobies, Eurasian Ruffe, which one day may make us all forget about the Zebra Mussel. 

But one thing is certain...If we take care of the shorelines and the water quality, there will be plenty of fish to catch and watch in the years to come.  And another thing is certain. Rideau paddlers will still be slicing through the water, but they may be just a little more aware of the watery world beneath them.  
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