Pollution, Habitat Degradation, Parasitic Sea Lamprey,
and Trillions of Quagga Mussels Exact a Heavy
Toll on Once Abundant Prized Lake Whitefish
by Scott Brown
MWA e-Newsletter Editor
A multi-faceted array of harmful manmade influences that have manifested over the course of the past one hundred years have taken a heavy toll on once thriving populations of Laurentian Great Lakes region lake whitefish. Known to have provided an important source of readily available protein that helped sustain native Americans living in the Laurentian Great Lakes region for thousands of years as well as for the first European explorers and settlers to the freshwater inundated region, abundant populations of native lake whitefish that once thrived within the waters of Lake Huron and Lake Michigan are now in steady decline.
Lake whitefish, scientific name Coregonus clupeaformis, are distributed throughout much of Canada and parts of the northern United States including Alaska and the Great Lakes region. Capable of growing to a weight of up to four pounds, and to a length of up to 22 inches, lake whitefish are related to salmon, trout, and char, and are members of the Salmonidae family. The high demand for lake whitefish is associated with the exceptional flavor of its flesh and commensurate popularity with fish markets and restaurants. Introduced to the savory flavor of lake whitefish in 1695 on his first venture into the Great Lakes region, the renown French explorer Antoine de la Mothe Cadillac commented that a “better fish cannot be eaten.” Representing 25% of the total annual catch of the commercial fishing industry in the upper Great Lakes region, highly profitable lake whitefish are perceived by many as the “unsung heroes” of a gradually declining regional fishing industry.
Lake whitefish are a bottom dwelling freshwater species that feed en masse on a shrimp-like creature called Diporeia as well as upon a variety of other aquatic invertebrates and small fish. Existing during the daylight hours in the cold dimly lit waters found at depths of between 100 and 300 feet, lake whitefish are known to migrate into more biologically productive shallower waters at night to feast upon emerging mayflies and midges. While larval stage and juvenile lake whitefish depend almost entirely upon tiny zooplankton for sustenance, lake whitefish that grow to lengths of three to four inches begin feeding upon bottom-dwelling animals such as snails, insect larvae, zebra mussels and fingernail clams which they continue to consume for the remainder of their adult lives.
Lake whitefish populations began their gradual decline in the Great Lakes in the early years of the 20th century as their vital near shore spawning grounds became severely polluted by the sheer volume of the waste created by hundreds of saw mills operated by the booming timber industry of the period. The successful introduction of exotic sea lamprey to the Great Lakes region also contributed to declining lake whitefish populations. In Lake Michigan, for example, rapidly reproducing and highly invasive populations of parasitic sea lamprey began to decimate native fish populations including high value species such as lake whitefish and other salmonids on a large scale beginning in the 1930s and 1940s.
Abundant populations of lake whitefish that once thrived in Lake Michigan and Lake Huron have also significantly declined in recent decades due to the presence of trillions of exotic invasive quagga mussels. Exotic quagga mussels are considered powerful aquatic ecosystem engineers due to their collective capacity to dramatically alter host ecosystem aquatic food webs by filtering out and effectively removing the phytoplankton that serves as a vital source of food for the zooplankton that larval stage and post-larval stage lake whitefish depend upon for food. In addition to an almost total collapse of juvenile lake whitefish supporting zooplankton populations in many areas, the near total absence of water clarity limiting phytoplankton in many areas of Lake Huron and Lake Michigan is effectively illustrated by the fact that water clarity now frequently exceeds the water clarity of Lake Superior. Scuba divers often report being able to clearly observe their dive partners exploring a ship wreck from the surface in water depths of up to two hundred feet. It is important to note that at the peak of lake whitefish abundance within both Lake Huron and Lake Michigan, each liter of lake water often supported between 100 and 700 lake whitefish sustaining zooplankton.
In addition to the harmful compounding influences presented by timber industry pollution and habitat destruction, the introduction of parasitic sea lamprey, and significant changes that have occurred to the otherwise moderately productive aquatic ecosystems of Lake Michigan and Lake Huron due to the presence and overall ecological influence of trillions of exotic invasive quagga mussels, lake whitefish populations have also dwindled in recent decades because they often swim in schools comprised of tens of thousands of fish – a fact that has made them a relatively easy target for well-equipped commercial fishermen.