Michigan anglers wonder why Lake Ontario salmon seem to be doing better: Part 2
Baitfish in both lakes face problems related to food web changes and invasive species, but salmon in Lake Ontario have an easier time filling their bellies. Several hypotheses as to why were presented at a recent meeting in Niagara Falls.
A look at long-term data sets shows that Lake Ontario has experienced many of the same lower food web changes seen in Lake Michigan. Total phosphorus available in offshore waters has declined in both lakes, indicating reduced productivity. Zooplankton communities have changed, not only due to reduced productivity but also because of invasive spiny and fishhook water fleas that prey on smaller native zooplankton. Alewife can prey on these invasive water fleas, but in doing so they add a link to the food chain, leading to less efficient flow of energy from plankton to predatory salmon.
A small opossum shrimp called Mysis became a more important food resource for alewife in both lakes after expansion of invasive quagga mussels and water fleas. The Mysis shrimp declined in both lakes as fish began to prey upon them, but subtle differences in habitat and behavior may make Lake Ontario Mysis more accessible to alewife.
The complex relationship among spiny water fleas, native zooplankton, and alewife has been called the ‘trophic triangle’, and with Mysis in the mix, this becomes a ‘trophic quadrangle’. At a presentation entitled, “Towards an Increased Understanding of Lake Huron Ecosystem Function”, Tom Stewart of Ontario Ministry of Natural Resources explained how changes in one part of the trophic triangle influence the whole food web. He also discussed possible reasons for differences between Lake Ontario and the upper lakes. One reason that makes intuitive sense is that nutrient-rich water flowing in from Lake Erie has provided a buffer from the worst of the ‘bottom-up’ effects seen in Lake Huron and Lake Michigan.
Each of the five Great Lakes has a unique mixture of habitat types and watershed characteristics that influence fish within the lake. It should come as no surprise that fishing opportunities vary from lake to lake. Long-term data on weir-returning Chinook salmon demonstrates that Lake Ontario salmon are consistently bigger. Age 3 females have averaged between 15 and 23 pounds since the mid-80s in Lake Ontario’s Salmon River, while similar fish have averaged between about 11 and 22 pounds at Lake Michigan’s Strawberry Creek weir.
Although differences in weir placement and operation make this an imperfect comparison, it is striking that the average Lake Michigan fish has weighed less than 15 pounds (the lowest recorded weight of Lake Ontario fish) for eight of the past nine years. The one exception was 2011, when returning age 3 females weighed over 16 pounds at Strawberry Creek due to a strong 2010 alewife year-class.
While 2011 proved to be a banner year for Lake Michigan, in terms of both Chinook salmon size and numbers, it appeared to be an exception to the norm. On Lake Ontario, 2012 was a banner year and only time will tell if such quality fishing is sustainable.
This two-part Michigan State University Extension article was based on information presented at the Great Lakes Fishery Commission’s Lower Lakes Meeting, which took place March 26-28 in Niagara Falls, New York.