This past Thursday, Nick Legler, a DNR Great Lakes Fisheries Management Biologist, came in to talk with us about Chinook salmon management in Lake Michigan. Chinook salmon are not native to the Great Lakes, but once the alewife population skyrocketed, different trout and salmon species were brought in to control them. Chinook and alewife are both pelagic feeders, and therefore Chinook did the best in controlling alewife populations. This worked great for a while, but now there are too many predator fish and not enough prey, which causes a lack of nutrition for the salmon.
Many forage surveys were completed, and results show that overall forage biomass is very low – the alewives aren’t reaching their typical size, and the salmon are consuming them at a younger age than normal (1-3 years). This proves to be more energetically costly for the salmon. Since quagga and zebra mussels have moved in, they have removed a lot of the smaller organisms that larval alewife usually eat, causing food shortages for them. This factor, along with the large number of Chinook salmon in the lake, is causing a top-down bottom-up effect and putting too much pressure on the alewife to survive.
Chinook salmon are currently raised in a number of hatcheries in the state that prove to be successful. However, reduced stocking of these fish may be needed in order to get the alewife population back up. It would be pointless to stock even more Chinook salmon, because without a main food source, they would not have a high survival rate.