The sauger (Sander canadensis) is a freshwater perciform fish of the family Percidae which resembles its close relative the walleye. They are members of the largest vertebrate order, Perciformes. They are the most migratory percid species in North America. Saugers obtain two dorsal fins, the first is spiny and the posterior dorsal fin is a soft-rayed fin. Their paired fins are in the thoracic position and their caudal fin is truncated which means squared off at the corners, a characteristic of the family Percidae. Another physical characteristic of Saugers are their ctenoid scales which is common in advanced fishes. Saugers have a fusiform body structure, and as a result saugers are well adapted predatory fishes and are capable of swimming into fast currents with minimal drag on their bodies. They may be distinguished from walleyes by the distinctly spotted dorsal fin, by the lack of a white splotch on the caudal fin, by the rough skin over their gill, and by their generally more brassy color, or darker (almost black) color in some regions. The average sauger in an angler's creel is 300 to 400 g (11 to 14 oz) in weight.
Saugers are a widely distributed fish species. Their historical range consisted of eastern U.S west of the Appalachian Mountains, mostly southern, central, and western U.S up into southern Canada. Sauger distribution and range has decreased from historical ranges because of degraded and fragmented habitat conditions. Sauger distribution within its home range varies by time of year because they are a migratory fish species. Saugers are more typical of rivers whereas walleyes are more common in lakes and reservoirs. In many parts of their range, saugers are sympatric with walleyes. Hybridization between saugers and walleyes is not unknown; the hybrids, referred to as saugeyes, exhibit traits of both species. Being intermediate in appearance between the two species, saugeyes are sometimes difficult to differentiate, but they generally carry the dark blotches characteristic of the sauger. Saugers, however, are usually smaller and will better tolerate waters of higher turbidity than the walleye. Saugers require warmer summer water temperatures of 20-28 degrees Celsius. The need for warm water temperatures is thought to affect the northern and western boundaries of their range.
Reproduction and life cycle
Saugers generally move upstream to spawn during March–May depending on where their home locations are. They move downstream to their home locations from April–July after their spawning period is over. Saugers have been known to travel between 10 and 600 km from their home to spawning location downstream. Habitat at spawning sites are less complex and diverse than home locations. Females prefer rocky substrate and pools to deposit their eggs. As females increase in length, egg quality and fecundity increase. However, it is thought that egg production begins to decline after age 6 in female sauger. Sexual maturity is reached between 2 and 5 years old. Other measures of sexual maturity are related to size. A sauger is considered to be an adult when it reaches 250–300 mm. Upon birth, larval saugers drift downstream before developing feeding tendencies and horizontal maneuverability. Juvenile saugers tend to develop in diversion canals and backwaters until autumn when they migrate upstream to their wintering habitat. Residing in diversion canals is a large source of mortality for juvenile saugers.
Sauger feed on a variety of invertebrates and small fishes depending on the time of year and size of the sauger. Channel catfish Ictalurus punctatus and freshwater drum Pylodictus olivaris are a midsize (300–379 mm) and large (>379 mm) sauger's main food source during spring. The diet of a small sauger (200–299 mm) is slightly different than a larger sauger's. Smaller saugers generally feed on benthic invertebrates, mayfly larvae, and catfish during spring and summer. Mid-size and large saugers feed mainly on fish from spring to autumn, but their diets alter during summer. Mid-size and large saugers feed predominantly on mayfly larvae but only during summer months. Freshwater drum Aplodinotus grunniens and gizzard shad Dorosoma cepedianum are dominant food sources for saugers of all sizes during autumn. Fish accounted for over 99% of a sauger's diet during autumn. Saugers also prey on shiners during spring and summer but they do not account for a significant part of their diet. Shiners are absent from a sauger's diet in autumn probably due to their availability.
Sauger are most likely to be found in large rivers with deep pools with depths greater than 0.6 m. Pools with depths less than 0.6 m are not likely to yield saugers. They encounter a variety of habitats because of their migratory tendencies. They are usually found in natural rivers because they have more abundant pools and their flow regime has not been altered by dams or diversions. They are still common in impounded river systems. Diversions and dams affect habitat and spawning areas of Saugers. Saugers are usually found in areas with high turbidity, low channel slope, low stream velocity, and deep water. Saugers tend to select pools with sand and silt substrates, and habitat features that provide cover from the river current. They tend to avoid runs and riffles. They are most commonly found in pools that are at least 1.5 m deep. They can also be found in shallower pools but in lesser numbers. There have been no observed differences in habitat preference for males and females. The amount of saugers observed will increase with mean summer water temperature, maximum water depth, and mean summer alkalinity.
Saugers face many conservation issues because of migratory barriers, habitat loss, entrainment in irrigation canals, and overexploitation. Dams and diversion canals prevent spawning in upstream habitats. Altering flow regimes in rivers affects turbidity, formation of pools, and temperature. All of which are important for the timing and success of spawning saugers. Long migrations are the main reason why saugers struggle in dammed or diverted river systems. Low water levels in periods of drought are the most detrimental to sauger populations because it strands eggs during spawning and prevents larval sauger from reaching their downstream locations. High death rates that occur during spawning are related to degraded and fragmented river systems. Mortality rates in autumn are related to exploitation by fishermen.
- NatureServe (2013). "Sander canadensis". The IUCN Red List of Threatened Species. IUCN. 2013: e.T202604A18235203. doi:10.2305/IUCN.UK.2013-1.RLTS.T202604A18235203.en. Retrieved 10 January 2018.
- Jaeger, Matthew. 2004. Montana's Fish Species of Special Concern: Sauger. Montana Cooperative Fisheries Research Unit. http://www.fisheriessociety.org/AFSmontana/SSCpages/Sauger%20Status.htm. (Accessed May 2011).
- Kuhn et al. 2008. Habitat Use and Movement Patterns by Adult Saugers from fall to Summer in an Unimpounded Small-River System. North American Journal of Fisheries Management. 28: 360-367. American Fisheries Society. 2008.
- Jaeger et al. 2005. Seasonal Movements, Habitat Use, Aggregation, Exploitation, and Entrainment of Saugers in the Lower Yellowstone River: An Empirical Assessment of Factors Affecting Population Recovery. North American Journal of Fisheries Management 25.1550-1568. American Fisheries Society 2005.
- Amadio et al. 2006. Abundance of Adult Saugers across the Wind River Watershed, Wyoming. North American Journal of Fisheries Management. 26: 156-162. American Fisheries Society. 2006.
- Graeb, Brian D.S., Mark A. Kaemingk,David W. Willis. 2007. Early Life History of Sauger in Missouri River Reservoirs. Department of Wildlife and Fisheries Sciences. Brookings, SD.
- Wickstrom, Gerald A. 2006. Seasonal Distribution, Movement, and Food Habits of Walleye and Sauger in Lewis and Clark Lake. South Dakota Department of Game, Fish & Parks. Chamberlain, South Dakota.