Wisconsin Muskellunge Waters: Life History of Musky

Distribution - The original muskellunge range in Wisconsin was generally confined to lakes and rivers in the drainage of the Chippewa River above Chippewa Falls, the Wisconsin River above Hat Rapids near Rhinelander, and the Amnicon River in Douglas County. The distribution has been extended, particularly to the south, by stocking. Wisconsin currently has no active program for hybrid muskellunge management. Some residual populations still exist, however. (See map).

Currently, fishable populations of muskellunge are found in 711 lakes and 83 streams in 48 counties. The heaviest concentration of lakes containing muskellunge is found in the head water regions of the Chippewa, Flambeau, and Wisconsin Rivers.

Ecology

Like all predators at the top of the food chain, muskellunge are rarely abundant. An average muskellunge lake has one muskellunge greater than 30 inches for every two to three surface acres of water. Using this average it is possible to estimate the total number of adult muskellunge in Wisconsin waters at about 200,000.

Muskellunge are found in a wide variety of habitats but seem to thrive best in larger lakes and flowages. Some good muskellunge lakes are fertile and shallow and have an abundance of submersed vegetation. Rivers contain muskellunge also, especially in areas of deep water and slow currents.

Typical muskellunge lakes in the native range usually have thriving beds of submersed aquatic vegetation. The broad-leafed pond weed (also called musky weed) is an excellent indicator of muskellunge habitat. Large lakes which have both extensive deep and shallow basins and tributary streams are preferred waters and are well suited to meet muskellunge food and cover requirements.

Muskellunge are lone, sedentary fish that usually lurk concealed among vegetation near channels, bars or rocky ledges and shoals. Muskellunge in some waters, however, will move offshore and remain suspended over deep water. Such behavior is usually associated with prey populations such as cisco. Individual muskellunge have home ranges that overlap with each other. They move very little during the winter when water temperatures are near freezing, but their range increases a great deal in spring when they move to spawning areas. During the summer their movements are intermediate, usually covering an area less than 20 Acres, but if water temperatures exceed 80 degrees Fahrenheit, their movement declines. Changes in food and cover, as well as temperature, affect movement patterns. Preferred summer temperatures are in the 70's degrees Fahrenheit.

Muskellunge are opportunistic predators, feeding on whatever is generally available. Adults eat fish primarily, but occasionally consume small muskrats, ducks and other live food. Certain soft-finned prey fishes such as suckers or cisco may be preferred. Young muskellunge begin feeding on live zooplankton a few days after they hatch. After four or five days of feeding, they switch to live fish, if available, but can continue eating zooplankton for about a month. After the muskellunge are 1 1/2 inches long, live fish are essential.

Reproduction

Sexual maturity depends upon size and age. Stunted fish tend to mature when they are younger and smaller. The majority of females mature when they are 32-33 inches and 6 or 7 years old, although some females mature when only 25 inches long. Likewise, most males mature when they are 28-29 inches long and 5 or 6 years old, while stunted males mature when they are 21 or 22 inches long. The larger the female, the more eggs she will produce. A very large fish may produce over 400,000 eggs.

The spawning period in Wisconsin extends from mid-April through mid-May. Optimum water temperatures are about 55 degrees Fahrenheit, ranging from 49-60 degrees Fahrenheit. Spawning usually takes place in shallow bays in water from 1 to 3 feet deep. A muck bottom covered with detritus and dead vegetation, or sometimes woody debris is the usual spawning site.

Females deposit eggs randomly over several hundred yards of shoreline. One or more males swim side-by-side with the female so that the eggs and milt are deposited simultaneously at intervals over the bottom. There is no parental care of the eggs.

The time it takes for the eggs to incubate varies with water temperature. Eggs hatch in 8 to 14 days with rising water temperatures ranging from 54-62 degrees Fahrenheit. Numerous factors can cause reproductive failures, however. Excessively cold water temperatures, fluctuating water levels during spawning, predation, the shortage of suitable food for newly hatched fry, and suffocation of eggs in bottom muck often seriously limit reproduction. Sediments in runoff flowing into streams, from such things as construction and development, can also settle over fertilized eggs, causing them to suffocate.

The danger of mortality from predation is ever-present from the egg to adult. Surprisingly, the most significant predators of muskellunge fry and small fingerling are relatively small fish such as bluegills, perch, rock bass and crappies. Even insect larvae sometimes destroy large numbers of muskellunge fry and fingerling. Some adult insects such as the back swimmer (Notonecta) are also known to prey upon small muskellunge.

Age and Growth

Growth of muskellunge can be highly variable, even among individual fish within the same water. Factors that can influence growth include fish age, food availability, type and size, lake type, seasonal temperature, sex, (male or female) and genetics. When conditions for good growth are not present, stunting can occur. Muskellunge populations in Wisconsin have been found comprising fish that are nearly 20 years old and still less than 30 inches in length.

As fish approach sexual maturity, differences in growth rates between the sexes become evident. Females grow faster than males and often have greater potential of becoming much larger. A generalized age and growth table is shown below, but remember these growth rates can be variable from lake to lake.

Average Length (inches) of Muskellunge by Age and Sex:

Typically biologists use a scale sample to determine the age of a muskellunge, but scales can often be unreliable, especially for old fish. Researchers in Ontario have found that a bone located under the gill flap (cleithrum) can be easily removed and used for age determination, greatly increasing the accuracy of the evaluation. Muskellunge have been aged up to 30 years old using this technique. Unfortunately, the fish has be to killed for the cleithra to be removed. Taxidermists are often requested to remove the cleithra from trophy muskellunge they mount and send them to archives in Ontario for age determination. Anglers having trophy muskellunge mounted should ask their taxidermists to remove the cleithrea and send them to the address below. In return, anglers are provided with the age of their fish, and biologists benefit by gaining more information about current muskellunge populations, which can aid in future management decisions.

An information package can be obtained from:

Cleithrum Project
Royals Ontario Museum
100 Queens Park
Toronto
Ontario M5S 2C6
CANADA

Please send cleithrum, lake name and county, length, weight, and date of capture.

Disease

Muskellunge can become infected by a number of diseases or parasites. Observations indicate that muskellunge are victims of protozoan, bacterial, and viral infections and sometimes suffer from secondary fungus infections. Lymphosarcoma is a malignant cancer of the lymphoid tissue and is usually fatal to infected muskellunge. Lymphosarcoma tumors appear as "red sores" made up of blister-like growths or pinkish-white lesions. These sores are usually found on the sides, fins, and head. Esocid herpesvirus, recently diagnosed in Wisconsin, appears as bluish-white blotches typically on the back and fins during spring. It is unknown whether or not the herpes virus affects survival. Muskellunge have also been found infested with fluke grubs (Neascus), tapeworm (Proteocepahlus) and horny-headed worms (Acanthocephala).

For more information, please contact:

Tim Simonson, Staff Specialist
(608) 267-7498