Lake Sturgeon: Separating Fact from Fiction

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In response to drastic declines in Lake Sturgeon abundance, a considerable amount of effort has been allocated to improving the understanding of species biology and population status, as well as stocking to replenish stocks in areas where their appeared to be essentially no Lake Sturgeon left. Provincial and Federal governments, the hydroelectric industry, various academic institutions and resource user boards such as the Nelson River Sturgeon Board and the Saskatchewan River Sturgeon Management Board have all contributed over the past 20 years. As it turns out, many of the commonly accepted facts about Lake Sturgeon biology and the factors attributed to historical declines in abundance appear to be over-simplifications, or in some cases outright fiction. It is time for a little myth-busting!

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Myth #1: Lake Sturgeon require vast expanses of barrier-free lake/river habitat to support self-sustaining populations.

In some systems (e.g. Great Lakes and their small tributaries), adult Lake Sturgeon historically migrated hundreds or even thousands of kilometres between feeding and/or overwintering areas to spawning locations at the base of falls or rapids. The construction of dams on many Great Lakes tributaries (generally low-gradient or slope) undoubtedly blocked spawning migrations of Lake Sturgeon. However, physical characteristics of aquatic ecosystems that Lake Sturgeon live in vary considerably across the species range, and we know now that the generality of Lake Sturgeon undertaking lengthy migrations does not hold in every type of system.

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In rivers that flow through the Canadian Shield like the Winnipeg and Nelson, Lake Sturgeon do not move (or need to move) nearly as much. Winnipeg River telemetry studies have revealed small home ranges for juvenile and subadult Lake Sturgeon; essentially, the vast majority remain within deepwater basins as small as two kilometres in length (e.g. Pointe du Bois GS to Eight Foot Falls), year-round, for years on end! Young Lake Sturgeon seem to rarely move through the river narrows that subdivide the river (e.g. Old Slave Falls, Scots Rapids, Sturgeon Falls, The Barrier, Otter Falls). Even adults, which have the capability to move great distances (based on observations in the Great Lakes area), rarely utilize all the habitat available to them between the upstream and downstream dams that represent true barriers to movement. This makes sense when you think about the habitat and the biology of the species.  Lake Sturgeon lack the burst swimming capability of salmon, and even prior to construction of dams, the numerous falls/rapids would have restricted how far Lake Sturgeon could move – going too far downstream, over a set of falls, would mean a fish could not make it back to its “home-range” section of river, where it had spent the vast majority of its life.

Another interesting thing we have also learned is that Lake Sturgeon located in different sections of Shield rivers are genetically distinct from each other, which provides strong evidence to suggest two-way gene flow (upstream and downstream) did not occur past various falls/rapids, likely since glacial recession ~7,500 years ago!

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Myth #2: Lake Sturgeon are extremely slow growing.

In the past people (biologists included) have erroneously declared that Lake Sturgeon are slow growing, but that is not really true.

Lake Sturgeon often grow faster than most freshwater species. What biologists should have said is that Lake Sturgeon are generally fast growing, but take a long time to reach maturity and spawn for the first time.  Males generally mature at 12 – 20 years of age, and females at 15 – 30. By the time a female spawns for the first time, she might weigh close to 40 lbs! However, we know now that there are exceptions to the generalities associated with size- and age-at-maturity; at Pointe du Bois on the Winnipeg River, male Lake Sturgeon as young as 6 years old (and ~3 – 4 lbs) as well as ~10 lb females (ages unknown) have been observed in spawning condition.

Myth #3: Lake Sturgeon growth is determined by temperature/latitude. Southern populations grow faster than northern populations.

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Previous studies attributed differences in Lake Sturgeon growth rates to temperature/latitude/length of growing season, but there is strong new evidence to suggest that other factors are equally if not more important.  Growth rate data from across the province of Manitoba were recently synthesized. The fastest growing lake sturgeon (which reached 90 centimetres by age 12) came from a section of the Nelson River located just downstream of Sipiwesk Lake, and the slowest growing Lake Sturgeon (~52 cm by age 12) came from Numao Lake on the Winnipeg River.  Most of the variation in Lake Sturgeon growth was attributed to differences in fish density (more fish = slower growth) and water velocity (faster moving water = slower growth).

Myth #4: The Lake Sturgeon is an endangered species.

The Committee on the Status of Endangered Species in Canada assessed several Lake Sturgeon “Designatable Units” (groups of populations that are geographically proximal, and presumably genetically similar) as “endangered” in their 2006 and 2017 assessments. However, deliberation by the Federal Government on whether to officially list the species under the Species At Risk Act is ongoing. It should also be noted that various organizations around the world also prescribe status of a species. The IUCN Red List of Threatened Species, which operates on a global scale, currently denotes Lake Sturgeon as “least concern”. Different Canadian provinces have assigned various designations and protections to Lake Sturgeon populations in their respective jurisdictions, and in some cases to individual rivers.  For example, a Conservation Closure was invoked on the Manitoba portion of the Winnipeg River (Ontario border downstream to Pine Falls) during the mid- 1990s that technically precluded all targeting of Lake Sturgeon by both subsistence fisherman and recreational anglers (by the letter of the law, catch and release angling has been illegal ever since the closure was invoked).

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Myth #5: Stocking is responsible for the recovery of Winnipeg River Lake Sturgeon populations.

While Lake Sturgeon stocking was conducted in the Winnipeg River during the 1990s and early 2000s, a growing body of evidence suggests that survival of the fish stocked was probably poor. There is little doubt that natural spawning and recruitment have been primarily responsible for populations having trended positively, some to the point where Lake Sturgeon density currently appears to be limiting growth rates (see Myth #3). The biologists and managers responsible for invoking the Winnipeg River Conservation Closure, as well as a similar closure on the upper Nelson River, deserve great recognition for helping restore the populations.

While stocking has been minimally influential on the Winnipeg River, it is quite the opposite on the upper Nelson River where the various reaches had been so depleted of Lake Sturgeon that natural recovery would have been, at best, a very slow process. Since it became standard practise to rear Lake Sturgeon to age-1 prior to release into the wild, the survival rate has increased dramatically. The road to recovery in the upper Nelson River is long, but Lake Sturgeon abundance is increasing, and the Nelson River Sturgeon Board (comprised of people from the communities surrounding the Nelson River) deserves a huge amount of credit for helping to facilitate the recovery!

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Myth #6: Lake Sturgeon can live to be 150 years old.

While young lake sturgeon can be aged relatively accurately via the examination of pectoral fin ray sections, a great deal of uncertainty surrounds estimates of age for larger Lake Sturgeon due to potential deposition of false annuli (tree-ring type growth), and compression of true annuli. Historical reports of “154 year old” Lake Sturgeon need to be taken with a grain of salt, because annuli counts for large fish have now been shown to bias age estimates considerably, and extrapolations are problematic.  In Lake Winnebago, Wisconsin (perhaps the best studied Lake Sturgeon population in North America) males and females are thought to rarely attain 40 and 80 years of age, respectively.

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Craig McDougall is a fisheries biologist, tech-savvy angler, and President of Angler’s Edge Mapping.

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