Successes and Failures of Large-Scale Ecosystem Manipulation Using Hatchery Production: The Upper Great Lakes Experience
Gary E. Whelan and James E. Johnson
Abstract.—The upper Great Lakes are the largest water bodies in the world whose ecological balance was and is owed to hatchery recruitment. This situation was caused by the loss of native predator stocks, the overpopulation of invasive alewives, other invasive species introductions, overharvest, physical habitat loss, and water quality degradation. In the 1960s, fish biomass in the Great Lakes was dominated by alewives that truncated the energy flow in the system. Episodic alewife die-offs littered beaches, destroying the shoreline tourist economies. The 1960s and 1970s saw the beginning of rehabilitation programs that included water quality initiatives, commercial fishing restrictions, intensive sea lamprey control, fishway construction, and the extensive stocking of the system with coho salmon Oncorhynchus kisutch, Chinook salmon O. tshawytscha, rainbow trout O. mykiss, lake trout Salvelinus namaycush, and brown trout Salmo trutta. These changes led to ecologically balanced fish communities and recreational and commercial fisheries with an annual value in excess of $2 billion, along with self-sustaining lake trout populations in Lake Superior. This fisheries management effort used 895,865,567 trout and salmon weighing 22,938,911 kg that cost, at minimum, $328,255,820 in 2002 U.S. dollars. In spite of these remarkable successes, critical problems remain, including the lack of lake trout rehabilitation and insufficient overall recruitment of predators in Lake Huron and Lake Michigan. Thus, Lake Huron and Lake Michigan, which are a continuous body of water, constitute the single largest body of freshwater in the world that is dependant upon stocking for ecosystem balance. Without stocking, they would revert to conditions experienced in the 1960s. The reason for reproductive failure of predator species in these lakes appears to be a combination of invasive species, overharvest, and habitat loss. These factors, along with the continued influx of new invasive species have slowed rehabilitation efforts in Lake Huron and Lake Michigan and cast uncertainty over the sustainability of the rehabilitation of Lake Superior. Without massive ecosystem level intervention, large portions of the Great Lakes will likely have to be maintained for the foreseeable future using hatchery recruitment.