Monthly Archives

August 2021

USEPA Survey Reaffirms that an Extraordinarily Abundant Exotic Invasive Quagga Mussel Population Continues to Dominate Lake Michigan’s Aquatic Ecosystem

Reporting that quagga mussels continue to be “major drivers and stressors” within the lake’s aquatic ecosystem, aquatic scientists assigned to the United States Environmental Protection Agency’s (USEPA) 180-foot Lake Guardian research vessel who recently completed their once every five-year survey of Lake Michigan have concluded that although the population of the exotic invasive mussels appears to have leveled off, the rapidly reproducing member of the Dreissena mussel family is becoming larger, and is occupying deeper areas of the lake’s basin. Enabled by the capacity to attach themselves to hard surfaces ranging from water intake pipes to the hulls of shipwrecks as well as to soft sediments, the filter feeding mussel, a native of the waters of Eastern Europe, now occupies more than one half of Lake Michigan’s 22, 406 square mile basin. According to scientists working aboard the vessel, the recently completed survey of the lake’s basin reaffirms that exotic invasive quagga mussels (scientific name: Dreissena bugensis) have become the dominant factor in Lake Michigan’ aquatic ecosystem.

First discovered in the Laurentian Great Lakes region in Lake St. Clair in 1988, quagga mussels represent one of two species of Dreissena mussels, the other being the now widespread zebra mussel (Dreissena polymorpha), that each entered the region via the ballast water discharges of trans-oceanic freighters navigating into the region through the St. Lawrence Seaway. Since their initial discovery over thirty years ago, quagga mussels have spread rapidly throughout Great Lakes and Mississippi River Basin states, and several other watersheds located throughout the eastern, central, and western United States, including the Colorado River, and Lake Mead, located in Nevada and Arizona. Both quagga and zebra mussels are capable of being introduced to other water bodies via microscopic larvae that are easily transported in ballast water, bilges, live wells, and other on-board equipment that holds water.

Although quagga mussels are capable of tolerating salinities of up to five parts per thousand, they have evolved to prefer the calcium carbonate rich freshwaters found in all of the Laurentian Great Lakes except Lake Superior. Unlike zebra mussels that prefer water temperatures ranging from 68° to 77° F (20° to 25° C), quagga mussels have evolved to prefer significantly cooler water temperatures ranging from 59° to 68° F (15° to 20° C). It is also known that water temperatures of 82° F (28°C), or greater begin to produce high mortality rates in quagga mussels. In contrast to zebra mussels that are more likely to be found thriving in near shore shallow water areas hosting higher water temperatures, quagga mussels are more likely to be found occupying off shore areas of the basin hosting water depths of up to 500 feet (152 meters), and inherently colder water temperatures.

Although the long term ecological effects of trillions of quagga mussels feeding upon the microscopic aquatic plants and animals that form the basis of the food chain in most lakes and rivers are not yet well understood, scientists working aboard the R/V Lake Guardian are concerned that an astronomical population of filter feeding quagga mussels are in fact gradually depleting a once abundant aquatic food chain that has a long history of supporting a robust Laurentian Great Lakes fishing industry. Moreover, the economic cost of managing the steadily escalating harmful influences of an extraordinary abundant population of exotic invasive Dreissena mussels is $500 million per year. Exotic invasive Dreissena mussels reduce the operational efficiency of power and waste water treatment plants by clogging water intake pipes, and are having an increasing negative influence upon the Great Lakes region’s lucrative recreation boating and sport fishing industries by completely covering docks, breakwalls, buoys, boats, and beaches. Littering beaches with millions of sharp edge shells, removing dead mussels from public beaches has also become a significant expense for municipal governments.

Scrappy Bluegill Thriving in Most of Michigan’s Inland Lakes

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For those of us who were lucky enough to spend our childhood living on or near one of Michigan’s thousands of inland lakes, the scrappy bluegill, also sometimes referred to as bream or sun perch, was often the first fish that many of us ever caught while dangling a hook, worm, sinker, and bobber from the end of a flimsy cane pole. Native to the eastern half of the United States, due to the fact that the rapidly reproducing member of the sunfish family gradually became one of North America’s most popular sport fish, and have therefore been intentionally introduced to many regions where they are not indigenous, bluegill now commonly inhabit the waters of lakes, lagoons, reservoirs, ponds, quarries, and rivers extending from Canada to northern Mexico.

Capable of growing to 9½ inches (.24 meter) in length, and achieving a weight of up to 12 ounces (340 grams), bluegill (scientific name: Lepomis macrochirus) may be differentiated from other commonly occurring members of the sunfish family by the six to eight dark vertical bars that adorns both sides of their compressed body, a namesake pale blue spot on the upper most lobe of their gill cover, a relatively small head and mouth, a dorsal fin that features nine to eleven spines, and by an anal fin defined by three spines. Bluegill possess an upper body that is dark olive-green in color that gradually blends to colors ranging from lavender, brown, copper, or orange on the sides, and a reddish-orange or yellow belly. It is interesting to note that adult male bluegills may be distinguished from the females of the species by the presence of brighter, more tense coloration patterns.

Preferring quiet waters found in small to mid-sized inland lakes or ponds, bluegills are most often observed in large numbers within habitats ranging from dense submerged aquatic plant stands located near the drop-off in water depths of up to ten feet to areas hosting shade induced cooler waters located under docks, swimming rafts, or overhanging tree branches. In addition to habitats defined by complex vegetative or woody structure that provide protection from predation, bluegills prefer habitats that are capable of supporting their voracious, non-stop foraging upon insects, insect larvae, small crustaceans, and worms.

Reaching sexual maturity within their first two years of life, bluegills are capable of achieving and sustaining prolific rates of reproduction. Responding to the arrival of late spring or early summer, bluegill begin their annual reproductive cycle as water temperatures reach 70° F (21° C). The process begins as male bluegills use their tail to create a sediment free dish shaped nest lined with gravel and stone in water depths ranging from 1.5 to 4 feet (.45 – 1.21 meter). Given the fact that bluegills are colonial nesters, areas of inland lakes characterized by ideal breeding habitat comprised of flat or gradually sloping areas of shallow water interspersed with dense aquatic plant growth, and/or woody debris will often host hundreds of the saucer shaped nests. Depositing their eggs within the stone and gravel lined areas of several adjacent nests, mature female bluegills are capable of producing up to 80,000 eggs per year. The survival of each nest’s offspring is promoted by the fact that females and males make genetic contributions to multiple nests. Following the creation of nests, and the deposition and fertilization of eggs, male bluegills aggressively guard their respective nests from predators, and help promote the viability of the fertilized eggs by preventing sediment from accumulating within the nest. Following a brief incubation period the eggs hatch, and the male of the species guards the hatchlings until they are mature enough to venture out of the confines of the nest, and into open water.