By Erling Friis-Baastad
It’s a lovely summer evening somewhere in the Liard Watershed of the southeastern Yukon. You’ve just landed a hard-fighting, plump, arctic char. Or maybe it’s a Dolly Varden. Or even a bull trout. Well, what the heck, you decide, supper by any other name…
The fact is that even scientists have been struggling to tell these fish apart. And not all scientists agree as to whether all populations of Salvelinus alpinus (arctic char), Salvelinus malma (Dolly Varden) and Salvelinus confluentus (bull trout) have been definitively and correctly identified.
“The three species look very similar. In some cases you can’t even tell them apart just by looking at them,” says Nathan Millar, senior fisheries biologist with Environment Yukon.
The species can look alike, but there are populations of fish within a species that can appear quite different from one another. “It depends on what they’re eating, where they’re living, what time of year it is,” says Millar. Dolly Varden are famous for their gorgeous colouration and markings; in fact, they got their name from the beautiful, plump, and beribboned daughter of the stalwart London locksmith in Charles Dickens’ novel Barnaby Rudge. But these fish are not capable of producing the bright orange and red colours all on their own. They ingest the pigmentation along with their food, says Millar.
Meanwhile, recent research on Yukon fish has identified two genetically distinct forms of Dolly Varden here: a northern form on the North Slope of the territory and in the Peel drainages, and a southern form in the Pacific drainage to the southwest. And then there are lacustrine (lake-dwelling forms), river-dwelling forms, sea-run (anadromous) forms, and even “sneakers,” male freshwater char that sneak in among the eggs of spawning sea-run females to add their own genetic signatures to the mix.
With the similarities between species and the great differences within species, no wonder people have been confusing Dolly Varden, arctic char and bull trout for decades. But does it matter? If they’re so similar, why expend all the effort to tell them apart?
It’s not a matter of simple scientific curiosity. The three species, long important food sources for northern people, are among the many wild creatures that are threatened by drastic changes to climate, and by encroaching industrialization and attendant habitat destruction. If we’re to effectively manage the remaining populations, says Millar, we have to be able to tell them apart.
And it’s not enough to tell species apart. Scientists must be able to differentiate the populations within a species. “This is the way we manage salmon,” he says, “by population, not just by overall numbers. At least that’s the goal.” Populations are studied as “conservation units” or “evolutionary significant units,” the building blocks of the species. “Each block would differ genetically so that you would want to preserve those blocks into the future, Millar explains. “If you didn’t pay attention to the blocks and you lost some of them, you’re losing biodiversity.”
So how do Millar and his colleagues establish a block?
Meristics, the study of body parts and segments, provides them with a number of related tools. These measure morphological aspects of the fish: length and width, number of spines, ratio of eye size to head size, and so forth. The number of folds in the pyloric caeca, a section of the digestive tract, can provide a clue to identity. And counting gill rakers, bony structures used to filter food out of the water, can prove very helpful. A fish with many gill rakers feeds primarily on smaller organisms, using the rakers to filter them from the water, while a fish with few gill rakers is likely one that subsists primarily on other fish.
Researchers are employing one of biology’s most effective new tools, genetic analysis. “You can use that kind of information to look at the history of how closely related two species are, how much of their genetic makeup do they share, whether a species arrived from two separate species combining,” says Millar.
“The other thing you can learn from that is where the fish were during the last ice age and how ice and glaciers have shaped the colonization and distribution of these fish today. For example, why do you find bull trout in the Liard and not Dolly Varden?
“Now that we know where different species are, we can use geography. If you are in the Liard (watershed) and catch a fish and you don’t know whether it’s a bull trout or a Dolly Varden, well, I can tell you it’s a bull trout because it’s the Liard.”
Bull trout are actually doing quite well in the Yukon, compared with others of their species further to the south, where there’s greater habitat loss and fishing pressure, says Millar. But some populations of Dolly Varden are of more pressing concern in the territory. Understanding how species behave within specific landscapes helps scientists make predictions, and issue suggestions and warnings when development restrictions and harvesting quotas are being considered.
This column is co-ordinated by the Northern Research Institute at Yukon College with financial support from Environment Yukon and Yukon
College. The articles are archived at www.taiga.net/yourYukon/archives.htm