Reproduction
Muskellunge in the Potomac River typically spawn in late April to early May when water temperatures reach 50°F for several consecutive days. Males migrate to spawning grounds first and await the arrival of fertile females. Courtship occurs and non-adhesive eggs are broadcasted over substrates covered by detritus and silt in shallow waters less than four to five feet deep.
Muskellunge are unique among members of the pike family in that they produce non-adhesive eggs that settle over potentially hypoxic/anoxic substrate instead of sticking to vegetation or other structures.
These traits suggest that habitat where larval development occurs may be a significant factor in reproductive success. Additionally, river flow plays a critical role in spawning success and survival of young fish. Major flow events disrupt spawning activities and prohibit newly hatched fish from feeding efficiently while extremely low flows minimize available spawning habitats within the river. High flows in the month of March, followed by receding levels through June present optimal conditions for muskie reproduction and survival.
Declines in muskie populations have been well documented and are largely attributed to the loss or alteration of suitable spawning habitat (1)
Reintroductions from stocking are not cost-effective due to the high post-stocking mortality of young-of-the-year fish and the greater costs associated with advanced fingerlings; therefore, protection of spawning habitats is very important in maintaining a self-sustaining muskie population.
Growth
Muskie are a long lived freshwater fish in the pike family Esocidae. Common to most fish populations, growth is typically fastest early in life and decreases over time as the fish reaches their maximum length and age. This species exhibits a sexually dimorphic growth pattern where females grow faster and live longer than males.
Figure 1 illustrates a length at age growth model for muskie in the Potomac River. Male and female muskie typically exhibit different growth rates as early as year five. To date, the oldest and largest individual verified from the Potomac River was 19 years old and measured 50.5 inches long.
Diet
Muskie are ambush predators that utilize a “lie and wait” tactic to capture prey. This species is considered a sight feeder that relies on keen vision and short-bursts of speed. Muskie are more adept to short burst style habits opposed to long slow cruising that is exhibited by some other fish species. This physiological characteristic is supported by deeper portions of white muscle that aid in recovery from a short-burst swimming behavior but fatigues rather quickly.
Contrary to popular belief, muskie consume a very small percentage of game fish such as smallmouth bass. Numerous diet preference studies indicate that this species prefer and target soft-rayed, cylindrical bodied fishes (i.e. sucker species) (2, 3)
Muskie fry feed primarily on plankton shortly after hatching. At roughly two inches in length, the muskie begins to target other fish species and even cannibalize on their own kind. Fish make up the majority of the muskie diet throughout the rest of their lives; however, some reports indicate that this species will prey upon birds, frogs, snakes, muskrats, and mice as well.
An apex (top) predator is opportunistic and will typically take advantage of an easy meal. This includes young, weak, and old or struggling prey. It is not uncommon for a muskie to engulf or attack a struggling fish on the end of an angler’s line, regardless of species, as this behavior triggers their predatory instinct.
Densities
Typical of most apex predators, muskies exist in relatively low densities. A mark – recapture population estimate of muskie in the Washington County portion of the Potomac River indicated that roughly 7-11 fish over 30 inches exist per river mile. Washington County supports the highest density of muskie within the freshwater Potomac.
Native Range
Muskie is only found in North America. Historically, muskie were (are) found in the Great Lakes region, upper Mississippi drainage, and the Canadian provinces of Ontario and Quebec. They were also (or are) indigenous to the Chippewa-Flambeau, Wisconsin, Ohio, Allegheny, and Cumberland River drainages in Wisconsin, Pennsylvania, New York, West Virginia, Kentucky, North Carolina, and Tennessee. Currently, Maryland is one of only eleven states in the U.S. to have self-sustaining muskie populations (4)
Threats
Threats to muskie populations throughout North America are habitat loss/degradation, pollution, overexploitation and diseases/pathogens. Disease and pathogens common to muskie include piscirickettsia (musky pox) and viral hemorrhagic septicaemia (VHS).
Large scale mortalities have been experienced by outbreaks of these infections in the past decade and have decimated some muskie populations where they occur. It is strongly recommended that anglers take extreme caution when fishing different waters.
- Always make sure that your boat and gear are dry and clean of any foreign debris in order to minimize the risk of transporting potential contaminants and invasive species.
- Delayed mortality from angling for muskie during periods of high thermal stress may be the largest component of total annual mortality.
Muskie are considered a cool-water fish making them more sensitive to warmer water temperatures (5). Summer water temperatures in the upper Potomac River often reach and can exceed the upper lethal limit reported for muskellunge at 85°F (5).
In fact, temperature data reveals increasing trends in the number of days that water temperatures reach or exceed 77°F over the past decade.
Limited information is available on muskellunge activity/behavior during periods of thermal stress; however, muskellunge have been found to selected cooler temperatures with less than ideal dissolved oxygen concentrations over areas with abundant dissolved oxygen at warmer temperatures during summer months when water temperatures reach or exceeded 85°F (6). Higher water temperatures can alter the oxygen affinity of hemoglobin to where it cannot take in an adequate supply of oxygen even if it is present. This condition is exacerbated during periods of physical exertion (ex: angling). Significant increases in blood glucose, lactic acid, and plasma potassium concentrations in muskellunge angled from warmer water temperatures has been documented (7). These physiological effects can increase catch and release mortality during the summer months. There is a delay in the time it takes for blood chemistry values to peak suggesting significant delayed mortality is possible post release (8).
During 2017 and 2018 Potomac River anglers reported catching and releasing a total of 21 tagged muskie while river temperatures exceeded 80°F. Ten of these fish, with an average length of 41”, perished for a mortality rate of 48%. This incredibly high mortality rate is stress from angling exertion and handling combined with thermal stress.
The Freshwater Fisheries Program recommends that anglers consider refraining from targeting muskie when water temperatures reach 80°F to reduce delayed angling mortality.
