The Alewife Fish In the Great Lakes

Who's on the Hook?

The invasive alewife (Alosa pseudoharengus) has profoundly impacted the Great Lakes ecosystem, creating an ecological disaster driven in part by a focus on sports fishing over native species rehabilitation and sound ecosystem management.

🐟 Ecological Disaster Caused by Alewife

The alewife, a small fish native to the Atlantic Ocean, became dominant in lakes Michigan, Huron, and Ontario after the native top predator, the lake trout (Salvelinus namaycush), was decimated by overfishing and the parasitic sea lamprey (Petromyzon marinus).

Impact on Lake Trout: Alewives interfere with lake trout recovery in several ways:

Predation: They prey on the early life stages, such as the fry (newly hatched young), of native lake trout.

Thiamine Deficiency Complex (TDC): Alewives contain high levels of the enzyme thiaminase, which breaks down thiamine (Vitamin B1). When adult lake trout (or other salmonids like Pacific salmon) consume a diet heavily reliant on alewife, it leads to a thiamine deficiency. This causes low survival rates and developmental issues in their eggs and offspring, effectively crippling natural reproduction.

Impact on Herbivorous Fishes: Alewives severely compete with and negatively impact native forage fish that are ecologically similar to herring (which is a general term often used for small, silvery forage fish). These native species were once so abundant that they supported massive commercial fisheries, providing a dietary staple and export opportunities. The most significant examples of these herbivorous native species that declined due to alewife competition and predation on their fry are:

Lake Herring (Coregonus artedi) or Cisco

Bloater (Coregonus hoyi) (one of the deepwater chubs)

The dominance of alewives led to massive die-offs in the 1960s, fouling Great Lakes beaches and creating immense political pressure to manage the invader.

🎣 The Role of Sports Fishing and Outdated Practices

To control the booming alewife population and establish a recreational fishery, state and provincial management agencies introduced Pacific salmon (primarily Chinook and Coho salmon) starting in the mid-1960s. This policy decision was a prime example of an outdated fishery practice that prioritized a quick economic fix—creating a non-native trophy sports fishery—over the difficult, long-term work of restoring native fish and the natural balance of the Great Lakes ecosystem.

Insistence of Sports Fishermen and Industry: The introduction of Pacific salmon was wildly successful, creating a highly lucrative charter fishing and tourism industry. The Chinook salmon, in particular, became the prized target, and its population relies almost exclusively on the alewife as a food source.

As alewife populations naturally declined, recreational fishing interests exerted significant pressure on management agencies to maintain high stocking rates for the popular Chinook salmon, even as the food base was shrinking.

This pressure also led to the elimination of commercial fisheries that harvested alewives by the early 1990s. Commercial alewife harvests competed with the stocked salmon for the same food source, so removing the commercial operations was seen as a way to leave more alewives for the sports fish.

Ecological Consequence: By eliminating the commercial fishery for alewife and maintaining high salmon stocking rates, fishery managers inadvertently exacerbated the ecological imbalance. This action essentially protects the alewife population—the primary driver of the ecological problems (TDC and native fry predation)—to sustain the non-native Chinook salmon sports fishery.

A financially advantaged group—the recreational anglers, charter captains, and associated tourism businesses—have thus indirectly leveraged their economic and political influence to maintain a management strategy that prioritizes their sport over the full restoration of the native, commercially and ecologically vital species like lake trout and cisco. This continues the ecological disaster by impeding the recovery of native