3.5.1.8 Macroinvertebrates

3.5.1.8 Macroinvertebrates

Limited information exists regarding the aquatic macroinvertebrates that may exist in the Platte River Basin or Seminoe Reservoir and streams within the Footprint of Potential Disturbance. The only macroinvertebrate study of Seminoe Reservoir took place in 1976. Numerous locations were sampled within Seminoe Reservoir and of these samples, two types of benthic invertebrates were identified: chironomids (nonbiting midges) and oligochaetes (Reclamation 1976). Both organisms play an important role in the exchange of substances between the bottom sediments and the adjacent waters (Reclamation 1981).

Chironomids dwell in lake sediments and may feed on detritus or plant and animal matter. Chironomids have a strong ecological role serving as a food resource for fish such as suckers, which then act as prey for predators such as Walleye. Oligochaetes are aquatic earthworms that burrow in bottom sediments and fill a similar ecological role as chironomids (Reclamation 1976).

In the Casper region, two species of fairy shrimp have been found and collected during amphibian surveys. Many invertebrates, including freshwater shrimp, live in seasonal wetlands (puddles, stock tanks, playas) alongside amphibians. Freshwater shrimp eggs may remain dry for several months or up to a year, then hatch after heavy rainfall. These shrimp are important prey for a variety of organisms, including amphibians and birds, and may not survive in wetlands with fish. Though freshwater shrimp may be eaten by adult amphibians, they may feed on amphibian eggs and larvae (WGFD 2013). Freshwater shrimp in Wyoming include several species of fairy shrimp and tadpole shrimp. Fairy shrimp look similar to saltwater shrimp but are much smaller. They are usually under an inch long and light beige in coloration, though some may appear to be bright green or orange. Tadpole shrimp have been found in other areas of Wyoming and may live in the Casper region as well. They look similar to tadpoles when swimming in the water, but when in hand, tadpole shrimp appear similar to miniature horseshoe crabs (WGFD 2013).

Similar to benthic macroinvertebrates, little information is known regarding crayfish in Wyoming (WGFD 2017c). Therefore, all native crayfishes are considered SGCN except for the virile crayfish (Orconectes virilis). Two crayfish surveys have been performed across the state: one between 1985 and 1987, and one from 2007 to 2009. In addition to the virile crayfish, three other species were identified: calico crayfish (Orconectes immunis), ringed crayfish (O. neglectus neglectus), and devil crayfish (Cambarus diogenes). Only the ringed crayfish was identified during both survey periods. The calico crayfish was the most widespread species in the Platte River Basin but appears to have been displaced in many places by the virile crayfish (WGFD 2017c).

In addition to crayfish identified from the two historical crayfish surveys, the Resident Fish Survey Study field teams observed a strong crayfish population within Seminoe Reservoir, specifically in Areas 1 and 2 (Figure 3.5-1). Crayfish were observed during the night electrofishing surveys as were visually observed scaling the rock walls and embankments in large numbers. Crayfish are assumed to be an important food resource to the fishery community of Seminoe Reservoir. During the Resident Fish Survey Study, Walleye were observed regurgitating their stomach contents, as a result of the effects from electrofishing