Last week, an excellent article in the Milwaukee Journal Sentinel covered some great news – lake whitefish are migrating inland to spawn and, in many cases, fish were running up into tributaries where they hadn’t been seen for 100 years.
One of the scientists featured in that article is Solomon David, a post doctoral researcher working jointly with Chicago’s Shedd Aquarium and the Center for Limnology’s Pete McIntyre on Great Lakes migratory fish. We asked Solomon a few questions about the migration and what the expanding ranges mean about the state of Wisconsin rivers.
Most people think of fish migrations as springtime phenomena – why winter? Is there an ecological advantage to end-of-year migrations?
Solomon David (SD): Many people think of spring migrations for fish like Northern pike and suckers, which are other focal migratory groups in our research in the McIntyre Lab. But Chinook salmon spawn in the fall, and lake whitefish spawn a bit later in the fall and early winter. There are advantages to spawning when it’s cold…for example, there are less hungry fishes around looking to eat the eggs. Many warm- (and even cool-) water fish slow their metabolism quite a bit in winter, and in many cases are not feeding or only feeding minimally, therefore there are less predators around to eat the eggs. Furthermore, when whitefish eggs hatch in early spring, other fishes are often more involved with spawning, so their young of the year (YOY) can outmigrate downstream and to lake habitats. In short, spawning in the winter can be somewhat safer than spawning in spring or summer, but there are of course ecological trade-offs to any given strategy.
Why do you think we’re seeing an increase in whitefish migrations? It’s a good sign, right?
SD: That is one of the key questions of our study. This sort of life history change is a big deal in fishes. Lake whitefish used to have numerous river-spawning migrations throughout the Great Lakes until around 100 years ago, then they dropped off. Spawning habitat loss is believed to be the main culprit, particularly pollution due to sawmills. Since then, there have been some positive improvements for the species such as sea lamprey control and the Clean Water Act. We believe that habitat improvement (since the major sawmill pollution) has greatly contributed to the reemergence of the whitefish river-spawning migrations. There are probably several other factors at work, such as population size and food availability, and we are looking into those too. Right now we are focusing on distinguishing different characteristics of river and lake spawners.
Overall we think this is a good sign; if it’s mainly related to habitat improvement, then that’s a positive result. Often times fishes and other organisms can serve as better indicators of habitat quality than human-made tests, so if the fishes are back, then that’s a good indication that something has changed (and we are hoping that it’s a change for the better).
What pressures did or are whitefish populations facing? What’s being done to address them?
SD: Lake whitefish have faced numerous pressures both in the past and presently. Spawning habitat loss due to sawmill and other pollution likely ended their river-spawning runs over a century ago. Invasive sea lamprey decimated populations, however eventual sea lamprey control helped the lake whitefish rebound. The loss (or near-loss in some areas) of diporeia, a major invertebrate food of the whitefish, due to invasive species impacts has also affected lake whitefish condition and diet composition. In terms of addressing these issues and other pressures, we have seen improved habitat thanks to restoration efforts in former lake whitefish river-spawning habitats. Multiple invasive species controls and regulations have also had positive impacts on lake whitefish populations and will hopefully continue to do so.
For our research, understanding why these migrations have come back, and more specifically, what the differences are between river and lake spawners will shed more light on how we can better conserve and sustain both the fishery as a whole and these migratory populations.
Are there places anyone interested could go to catch a glimpse of whitefish migration, or is it not as stellar viewing as other fish species?
SD: It’s tough to catch these migrations without a boat…and it’s really COLD when they are running! We were just out a couple weeks ago, and they were migrating up toward the dam on the Menominee River (they obviously couldn’t get any further than the dam). It was windy and snowing and our nets even froze on occasion, but the whitefish were indeed running. Without a boat there is not much to see, although later in the winter anglers have been successfully catching them while ice fishing (migrations are generally over by this time, however). On smaller rivers, with a boat, or potentially from a downstream dam one may be able to catch a glimpse, but they are more elusive and fewer in numbers than their salmonid cousins.
To see a Journal Sentinel slideshow on white fish migrations, go here. To read about what other research Solomon is up to, visit his website. And, of course, check out the Shedd Aquarium’s Great Lakes Program!