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| December 03, 2019 Post 108 |
| fish update |
A favorite of fishermen is the chinook salmon, a west coast native that grows quickly in Lake Ontario reaching up to 30 pounds in just a few years. Chinook eat almost exclusively alewives, and it’s the alewife supply that is a concern.
In the 1950s and 60s, when for various reasons most of the lake’s top predator fish were scarce, alewife populations exploded throughout the Great Lakes. When they moved inshore in late spring to spawn they suffered shock from abrupt changes in water temperature and died. The resultant masses of rotting “mooneyes” prompted the salmon stocking program that started in the 1970s in part to help clean up the excess a
Recently, fishery managers have become concerned about the population of this once overabundant little bait fish and its relationship to the population of chinook salmon. The salmon showing up in the anglers’ coolers last summer were not as plump or heavy as they used to be. Biologists suspect the salmon are spending more energy to find less food in the form of alewives.
Each year trawl surveys measure the abundance of bait fish throughout the lake and recent surveys suggest the alewife population is declining. Alewife can live up to ten years in the lake. Past surveys showed samples of alewife of various ages. In 2019 many of the larger alewives were all the same age. A single large “year class” of older fish suggests less than healthy growth and survival of younger alewives in
There may be several reasons for this. Alewives winter in the deeper waters of the lake. They prefer temperatures between 52 and 66 F and severe winters can cause a lot of mortality. Cold late springs can also decrease their abundance. A late cold spring delays the movement inshore of spawning alewife. The later they spawn the less time the young fish have to grow before the following winter. The smaller fish are more prone to winter’s stresses.
Yet another factor affecting alewife survival is their own food supply. The little bait fish do well if they have a good supply of nice big zooplankton to eat. Recent changes in the types and abundances of the various water fleas and other microcrustaceans in the lake may be impacting their growth and survival. All else being equal, a chinook salmon ( like the alewife) prefers one large meal to a number of small ones since it takes less energy to snap up a single big juicy prey item than to chase down several little ones. If the planktonic critters get smaller on average because of predation or competition from a new invasive species arrival, the effect might ripple upwards through the food chain.
Many of the diatoms, zooplankton, crustaceans, and other species present in the lake since glaciation are now competing with exotics introduced from east coast estuaries or from the brackish waters of the Caspian, Black, and Azov seas. In some cases our native food web components are either extinct or close to it, replaced by these invaders.
There are some efforts under way to restore the native bait fishes that once supplied lake trout and Atlantic salmon with food. We’ll explore the potential implications for the fishery in a future article. For now, it looks like the hatchery staff will be producing fewer Chinook salmon fingerlings next year in order to give the alewife population a chance to recover.