Lake Michigan anglers can expect fewer large Chinook salmon in 2016
Volunteers with the Salmon Ambassadors program found that medium-sized Chinook salmon were relatively scarce last year.
Great Lakes salmon anglers often assume that large Chinook salmon are “four-year-old” fish that are nearing maturity, and that the largest fish they catch are four-year-olds. In fact, most Great Lakes Chinook salmon mature and die before reaching Age 4. Fast-growing fish are particularly likely to mature earlier, so the Age 4 Chinook salmon that anglers do catch usually are not their largest fish, either.
Even so, the length of a salmon can provide a rough idea of the fish’s age. Growth rates vary from year to year, but in recent years the majority of Lake Michigan Chinook salmon over 30 inches long have been Age 3 fish. Chinook salmon from 20 to 30 inches long are most likely Age 2 fish, and those under 20 inches long are typically Age 1 fish. Remember that these are rough approximations, though. There is considerable overlap in length among age groups.
For anglers, the size of the fish is more important than its age anyhow. Anglers might enjoy catching big fish, but normally medium-sized fish are much more abundant in catches. This is a good thing because many small fish die before they get the chance to grow to larger sizes. Very small fish tend to be less common in angler catches — not because they are less abundant, but because anglers use baits and fishing methods that are not geared toward catching the smallest fish.
In 2014, volunteers with the Salmon Ambassadors program found what we would expect in most fisheries. Medium-sized (20- to 30-inch) Chinook salmon were more abundant than larger (and most likely older) salmon. In 2015 they found something very different. Large (30-inch and above) Chinook salmon were more prevalent in 2015 catches than smaller fish (see graph).
It may be tempting to blame this lack of small fish on the 50% stocking reduction that was implemented in 2013. Indeed, the stocking cut was designed to reduce the number of salmon in Lake Michigan and ease predation on declining bait fish (alewife). However, the biggest drop was not of stocked fish, but of wild fish.
In fact, Salmon Ambassadors data show that 53 percent of wild fish caught in 2014 were 20 to 30 inches long and this dropped to 33 percent in 2015. This reduction in medium-sized (mostly Age 2) Chinook salmon could translate to a drop in catches of large Chinook salmon for the 2016 fishing season.
That is bad news for the fishery in the short term, but not necessarily in the long term. Fewer predators in the lake may give open water baitfish a chance to rebuild their populations.
The Salmon Ambassadors program is an angler science project led by Michigan Sea Grant and Michigan State University Extension, and funded in part by Detroit Area Steelheaders. Anglers who volunteer for the program share information on wild and stocked catches with one another—and with biologists.
Volunteers track the length of each Chinook salmon caught over the course of the fishing season and look for a clipped adipose fin that indicates a stocked fish. At the end of the season, volunteers complete a short survey and return their data sheets. Results from 2015 were released in March 2016.
Michigan Sea Grant helps to foster economic growth and protect Michigan’s coastal, Great Lakes resources through education, research and outreach. A collaborative effort of the University of Michigan and Michigan State University and its MSU Extension, Michigan Sea Grant is part of the NOAA-National Sea Grant network of 33 university-based programs.