Asian Carp Study
The bighead carp (Hypophthalmichthys nobilis), a cyprinid from China introduced by aquaculturists in 1972, has since escaped into the Missouri, Mississippi, and Ohio rivers. An additional Asian carp species, the silver carp (H. molitrix) has also escaped from aquaculture facilities and has been found in South Dakota waters of the Missouri River below Gavins Point Dam. Gavins Point Dam forms a barrier to upstream migration by these exotic Asian carp species. How larval and juvenile Asian carps interact with the native Missouri River fishes is currently unknown. The high fecundity and rapid growth of Asian carp has created concern regarding the potential competition with native fishes for limited phytoplankton and zooplankton resources. By age-3, bighead carp attain lengths > 375 mm which likely precludes this species from predation by Missouri River piscivores.
To assess the rearing habitats used by young-of-the-year (YOY) Asian carp and document composition of YOY fish assemblages, multiple gears were used in multiple habitats to collect larval and juvenile fishes throughout the summers of 2003 and 2004. Samples were collected above and below Gavins Point Dam to compare fish community assemblages in areas with and without Asian carp. In deep-water macro-habitats with significant flows (e.g. inside bends, outside bends, main channel cross-overs, tributary mouths, secondary connected channels), larval fish nets were used to collect drifting larvae near the surface. Fishes were collected with small-meshed bag seines and minnow traps in shallow water bars in four macro-habitats: inside bends (ISB), outside bends (OSB) secondary connected channels (SCC), and secondary channels non-connected (SCN) characterized by reduced flows or stagnant waters. Flow, turbidity, water temperature, and dissolved oxygen were measured on each date within each macro-habitat.
During summers of 2003 and 2004, larval fishes were collected on seven dates from May through September in the Missouri River below Fort Randall and Gavins Point dams. Additionally, samples were collected directly in the James River mouth just downstream from South Dakota Highway 50 Bridge, an area where adult silver and bighead carp have been captured. For each sample, two conical zooplankton nets (0.5-m diameter, 3-m length, 500-μm mesh) were soaked from 1 to 5 minutes, depending on detritus loads, just below the surface. Fishes were collected by anchoring the boat in the current and collecting drift (i.e. drift samples). The volume of water filtered was measured with a mechanical flow meter positioned in the center of each net. Over 450 larval fish samples were collected from the Missouri River below each dam in each year for a grand total of 2061 samples. A total of 550 larval fish samples were collected downstream of Fort Randall Dam in 2004 and 451 samples were collected in 2003. A total of 552 larval fish samples were collected downstream of Gavins Point Dam in 2004 and 508 samples were collected in 2003. In the James River, 42 samples were collected in 2003 and 56 samples were collected in 2004.
Juvenile fishes were collected with three gear types (bag seines, mini-fyke nets, and minnow traps) in shallow water habitats because the susceptibility of juvenile Asian carps to any gear is currently unknown. Juvenile fish collections from shallow water bars occurred in July, August, and September at the same study locations and macrohabitats used to collect larval fishes.
Fishes were collected during the day with a bag seine (30 ft long, 6 ft deep with a 6 x 6 x 6 ft bag, ¼ inch mesh) and catch-per-unit-effort (CPUE) was recorded as numbers of fish/m2. We conducted 439 seine hauls for juvenile fishes in 2004, an increase of over 100 hauls from 2003 (N = 333). In 2004, 210 seine hauls were conducted downstream of Fort Randall Dam and 229 seine hauls were completed downstream of Gavins Point Dam.
Four types of minnow traps were set overnight from May to September with CPUE recorded as numbers of fish per net night and numbers of fish per hour. Minnow traps were set early in the year to assess first occurrence of cyprinids in the Missouri River in late-spring and early-summer. The minnow traps were generally set in log jams and other sheltered habitats that were not accessible by seining. We completed over 100 net nights of effort in each river reach downstream of Fort Randall and Gavins Point dams for each type of minnow trap in both years (grand total 456 net nights). Two galvanized metal conical trap types (¼ inch and 1/8 inch mesh) had two 2.25-inch openings at each end were used in both years. We discontinued use of the large wire square-box trap and the collapsible brown nylon box trap due to low catches in 2003.
Mini-fyke nets (3 mm mesh, 1.2 x 0.6 m frame, 4.5 m long lead) were set overnight with CPUE recorded as numbers of fish per net night and numbers of fish per hour. At each upstream and downstream location 16 nets were set from May through September with at least two nets placed in each macro-habitat present (ISB, OSB, SCC, and SCN). We completed 32 net nights of effort for the mini-fyke nets at both sample sites downstream of Fort Randall and Gavins Point dams in 2003 (grand total 128). Downstream from both dams, we completed 135 total net nights of effort in the Missouri River with mini-fyke nets in 2004.
In both years, we did not notice any YOY bighead and silver carp in our seine or mini-fyke net samples. However, YOY Asian carps can be mistaken for gizzard shad Dorosoma cepedianum and some of our seine hauls and net sets had catches exceeding 100 fish. Therefore, definitive documentation of the absence of YOY bighead and silver carps downstream of Fort Randall and Gavins Point dams awaits the completion of all fish identifications in the laboratory. Juvenile silver carps exhibit the same jumping behavior as adults when startled (Duane Chapman, USGS Columbia, MO, personal communication). At both sites in both years we did not notice any small jumping silver carp. However, in both years, we observed adult silver carp jump in the mouth of the James River.
An additional exotic species of concern is the zebra mussel Dreissena polymorpha and planktonic veligers have been collected from Lake Francis Case (upstream of Fort Randall Dam) and near the Verdel Boat ramp on the Missouri River (above Gavins Point Dam). During both years of this project, we placed submersible temperature loggers in the Missouri River below Fort Randall and Gavins Point dams (N = 15 in 2003 and N = 22 in 2004). Each logger was protected with a PVC sheath which essentially acts as an artificial substrate sampler for macroinvertebrate colonization. We observed no attached zebra mussels at all sites in both years. Only caddis fly (Trichoptera) and midge (Chironomidae) larvae were observed colonizing on the temperature loggers.
