Michigan anglers wonder why Lake Ontario salmon seem to be doing better: Part 1

Sometimes the grass only seems greener on the other side. Lake Ontario continues to produce big salmon while Lake Michigan fish sizes are down. Chinook salmon catch rates are at all-time highs on both lakes, but this is a sign of trouble on Lake Michigan.

 

Salmon fisheries in Lake Huron and Lake Michigan have seen big changes in the past decade. In Lake Huron, Chinook salmon disappeared from much of the lake after their primary food source, the invasive alewife, crashed in 2004. In Lake Michigan, the abundance of large, old alewife has declined along with their caloric value. Although salmon are still abundant in Lake Michigan, their size has declined.

These changes have hurt coastal communities on Lake Huron and led to concerns that Lake Michigan may follow the same path. In looking for an explanation, two possible explanations have emerged.  Broadly speaking, the ‘bottom-up’ explanation is that invasive quagga mussels have reduced the productivity of open waters while the ‘top-down’ explanation is that salmon are too abundant. Both situations could lead to problems for alewife and ultimately spell disaster for salmon.

This leads into the question – did Lake Ontario’s fishery really escape the problems of the upper lakes?

Reports from New York suggested that 2012 was a banner year for Lake Ontario salmon fishing. The latest data from biologists confirms this. Catch rates were at an all-time high in 2012. But wait – doesn’t this suggest top-down effects? Lake Michigan also recorded all-time high catch rates for charter anglers in 2012 and it was considered a warning sign.

The difference is in the size of the salmon. In general terms, it is possible to have big fish or lots of fish, but not lots of big fish – at least not for an extended period. In Lake Michigan, salmon were small last year. Not a single Chinook salmon was entered in the Michigan DNR’s Master Angler program in 2012.  The minimum entry weight is 27 pounds for a kept fish. 

Contrast that with Lake Ontario, where a 30-pound Chinook was needed to place in the top ten fish caught and entered for each week of the seven-week Great Ontario Salmon Derby. The average angler-caught age 3 Chinook salmon weighed 23 pounds in New York waters last year, and the average age-2 weir-harvested salmon from the Salmon River was comparable in size to fish of similar age taken in 1986.

When over-abundant salmon are causing depletion of alewife, we expect to see older alewife disappear. Large salmon prefer large food and only turn to eating young alewife if older, larger alewife are not available. This has happened on Lake Michigan, but on Lake Ontario, the abundance of large alewife has actually increased over the past couple of years.

Alewife condition is also on the rise in Lake Ontario, which is surprising because this measure of a fish’s weight relative to length fell sharply in Lake Michigan after the arrival of quagga mussels. A basin-wide map of quagga mussels suggests that they are even more problematic in Lake Ontario than in Lake Michigan. Both lakes saw a decline in Diporeia after the quagga invasion, but the loss of this important alewife food seemed to take a greater toll on Lake Michigan alewife.

Part 2 of this article from Michigan State University Extension addresses possible reasons for the differences between Lake Ontario and Lake Michigan fisheries.

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