Chapter 6: Biology and Natural History of Silver Carp
Silver carp Hypophthalmichthys molitrix occur in a variety of freshwater habitats including large rivers and ponds, lakes, and backwaters receiving flood waters or are otherwise connected to large rivers (Berg 1964; Kaul and Rishi 1993; Finley 1999). Silver carp also have been introduced widely to ponds, lakes, reservoirs, and canals where they grow well, but can rarely spawn and recruit without access to an appropriate riverine habitat. Silver carp prefer open areas (Abdusamadov 1987) and eutrophic zones (Robison and Buchanan 1988) of standing or slow-flowing waters (Berg 1964; Rasmussen 2002) and occupy the upper and middle layers of the water column (FAO 1980; Shetty et al. 1989). In its native range, mature silver carp migrate from lower river reaches and connected lakes to areas with swift currents in the spring for breeding (Berg 1964; Konradt 1965), often to river mouth areas (Berg 1964). Eggs and larvae drift downstream to floodplain zones (Froese and Pauly 2004). After moving to areas with rapids during high water stages to spawn, adult silver carp typically return to main channels, reservoirs, or lakes (Nikolsky 1963; Chang 1966). As juvenile silver carp approach maturity, they begin migrating to spawning grounds. For example, juvenile silver carp were found to feed for 4–5 years in lower reaches of the Amur River before gradually migrating up the river. Two years later, they reached the Malmyzh region after traversing 500 km. They then ascended an additional year before arriving at the main spawning grounds (Gorbach and Krykhtin 1989).
In the United States, data from a 2002-2004 telemetry study by Chapman indicate that adult silver carp in the lower Missouri River, like bighead carp Hypophthalmichthys nobilis, usually used low velocity areas behind wing dikes, especially areas more than 3 m deep (Figure 5.1). Silver carp also preferred spur dikes to wing dikes, did not use sandbars unassociated with wing dikes, and only used undiked outside bend habitats when moving between locations. Silver carp in the Missouri River occupied primarily low velocity water more than 3 m deep in all months of the year. Silver carp also used low velocity sections of Missouri River tributaries (Figure 5.2). Adult silver carp aggregate in pool habitats to overwinter (Berg 1964; Abdusamadov 1987; Gorbach and Krykhtin 1989). Preliminary data from telemetry and depth-temperature archival tags implanted in the fish (Chapman) indicate that silver carp in the Missouri River are active in winter, with activity slowing at under 4°C and little movement occurring at temperatures below 2°C. In that study, silver carp differed from bighead carp in that they used Missouri River tributaries less than bighead carp and used them mostly in summer, rather than winter.