What’s killing Ottawa River sturgeons?
On the weekend of Aug. 23, a large fish washed up dead on the sandy shores of Constance Bay, overturned on its thin white belly, strange little whiskers pointing to the sky.
It was a sturgeon — more properly, a lake sturgeon — about four feet long and likely weighing in excess of 30 pounds. Neighbours, beach-walkers, began to chatter. Not only was it a rare sight, but it wasn’t the first one this summer.
“I’ve had confirmation of five dead sturgeon found between the Lighthouse and the Point Beach in the past seven weeks,” Gerry Blyth later wrote, in describing a stretch of about two kilometres of the Ottawa River west of the city.
A resident of the shoreline for 31 years, he’d never seen a single dead sturgeon before. The question leapt to mind: Was something killing the most monstrous thing in the river, prehistoric fish that live for decades and can grow to six feet or even longer?
Well, no one is sure, and it is possible this is a strange clustering that has a perfectly sound explanation, like a natural die-off or mortality due to an angling misadventure.
Or not. The Ottawa, because of the scorching summer — July was the second hottest on record — is unusually warm right now and a quick call to a biologist reveals sturgeon are under stress if the water gets cooking. So begins the detective work. The City of Ottawa, it turns out, carefully tracks the temperature of the river at its two drinking-water intakes. (The precise reading actually affects the water treatment process.)
In July, the average temperature of the river at Britannia was 24.9 C, a full 1.5 degrees higher than the 10-year average of 23.4. August was higher as well, with average readings so far this month of 24.6 C, versus the historic average of 23.6 C.
And something else: In three of the past 12 years, the temperature of the river never rose above 25 C. Not for one day. This year, it has exceeded 25 C on 26 days, the highest number since at least 2009.
(The flip side of this is that the number of days that represent prime spawning temperature w— an important trigger for egg laying/fertilizing — was vastly reduced. There were only eight days in 2020 when the temperature was between 11 and 15 C. Last year, the number was 34.)
The Ottawa Riverkeeper was keenly interested in all this.
In-house biologist Katy Alambo has canvassed some sturgeon experts and discovered that, indeed, the giant bottom-feeding fish are under stress when the water gets too warm, as warmer water contains less dissolved oxygen.
“Fish are very susceptible to rapid changes in temperatures,” she said Friday. “They can cause physiological stress to fish, lead to changes in the immune system and make them vulnerable to pathogens or viruses.”
She wondered, too, about periods of torrential rain this summer and whether the run-off was pumping in extra nutrients.
There is likely no cause for alarm. Neither the Ministry of Natural Resources and Forestry nor the Riverkeeper have had any reports about large fish dieoffs on the Ottawa this summer, sturgeon or otherwise.
Blyth, meanwhile, said the discovery of the dead sturgeon sent him on an online dive about possible causes. There are, in fact, a good number of scholarly articles about lake sturgeon in eastern North America, including in the Ottawa.
Among the findings? They like flowing watercourses and the damming of major rivers has had a detrimental effect on populations just about everywhere, including here. Not only that, adds Blyth, but the way some dams practise “peaking” — or alternating between still and rushing water — can also negatively affect the spawning period.
There is a lot of lore about sturgeon on the Ottawa. Some of it is even true.
In March 1931, the Globe and Mail reported a specimen weighing 216 pounds was caught in the Ottawa near Montebello. In 1952, a fisherman near Davidson, Que., was in disbelief after a 35-pounder jumped right in his boat.
The Ottawa once had a thriving commercial fishery and, in 1898, more than 65,000 pounds were harvested. The Pembroke Observer, in the 1950s, carried a photo of sturgeon stacked on shore like cordwood: all to be used as fertilizer, which seems a horrible waste.
With their outer plates and spiky ridges, they are both distinct-looking and exceedingly long-lived, some lasting more than 100 years. Their life cycle is unusual, only becoming sexually mature after 15 to 18 years, while females only spawn every second or third year.
Should any more dead sturgeon show up, the Riverkeeper would like to know. Alambo asked that residents record the time and place, take photos and note anything unusual about the circumstances.
And be not afraid. Sturgeon, who would have thought, have no teeth.