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Yellowknife Lakes

Bluefish Lake, NWT. © Paul Vecsei (3)

The final frontier in exploratory fish biology

For an ichthyologist with a Ph.D., my fall assignment sounded routine: a basic lake-wide survey of fish in a small waterbody above the Northwest Territories Power Corporation (NTPC) Bluefish hydroelectric plant near Yellowknife, as part of ongoing monitoring. Sure, I liked setting nets in the abyss of mystery bound Great Slave Lake.

It looked uneventful to say the least. And by the standards of a big lake aficionado, it was, well, the size of a pond. For this work, I was once again in the company of Damian Panayi, a wildlife biologist and colleague. We went about setting the nets at dusk and waited till early morning for the pull. Our base was the Bluefish construction camp dormitory and it was a bustling place.

At the break of dawn, we were back on the water. Our first deep water station net pull had some small whitefish. But what appeared to be juvenile whitefish were, in fact, mature adults. This could only mean: either they were dwarf forms of the common lake whitefish or similar species, or it was something different. As we rushed back towards shore, I already knew what we had. These were likely pygmy whitefish and we had stumbled upon one of the most significant species range extensions in modern times. Until this capture, there was a 1,000-kilometre gap in pygmy whitefish presence between known populations in Great Bear Lake and Lake Athabasca. I knew this was big news, but in science, there is a lengthy procedure required to make your case to the scientific community before such a claim could go public.

So to the laboratory we went and started on morphometric (proportional/ratio) and meristic (enumeration) measurements. Next, eggs from the females were counted. Female pygmyies have low fecundity and I was stunned but glad to see egg counts in the low 300 range as opposed to 10,000 as seen in round or lake whitefish. We also referred to the literature as to morphological and biological characteristics that are unique to pygmy whitefish and determined if our specimens shared those traits. All good so far. And finally, the low number of scales along the midline sealed the deal.

But that’s not the end of the story. In the same net pull, we caught a kaleidoscope of small ciscoes as well. Ciscoes are those silver fish known as Tulibee but also encountered by dip-netters at Tartan Rapids near town. Now I was really in my element. I deduced that these ciscoes represented unique and likely recent local adaptations and even differed from the species flock of ciscoes in nearby Great Slave Lake. Imagine the post Ice Age lakes around Yellowknife as the Galapagos Islands as seen by Darwin during his famous expedition aboard the Beagle in 1835. Darwin found the different islands occupied by finches of differing beak shapes and sizes. He postulated that a species of finch reached the islands and eventually evolved radically different beak shapes and sizes. This process in which one species gives rise to multiple species that exploit different niches is called adaptive radiation. And that’s exactly what our cisco catch seemed to be. As on various islands where finch species have become adapted for different diets, our little ciscoes displayed differences in head shapes, mouth sizes and, most importantly (and the equivalent of the Darwin finch beak), gillraker counts. Gillrakers are the comb-like food-filtering structures attached to the gill arch inside the mouth of ciscoes. The different niche availabilities have allowed a post-ice age re-colonizing cisco to radiate into a multitude of forms, each best suited for feeding on a particular resource.

So Bluefish Lake offers us a window into a moment in time where evolution is captured in its later phases, finalizing its “new products.” Maybe this process occurred over a greater area and the deep hole in Bluefish Lake is their last refuge under changing and shrinking waterbodies. Indeed, the multitude of lakes around Yellowknife represent the final frontier in exploratory fish biology.

Paul Vecsei
Paul Vecsei (Ph.D.) is a Fisheries Biologist with Golder Associates Ltd. in Yellowknife. Golder has been working for the Northwest Territories Power Corporation (NTPC) in assessing the fish fauna of Bluefish Lake since 2011.