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60 Spargenium eurycarpum). In this study, the female crayfish, by eating the grazing snails, improved plant growth while the male crayfish grazed on the plants and reduced their growth. 24 The Northern crayfish will compete with other crayfishes. Northern crayfish introduced into the Patapsco River drainage in Maryland displaced the native Spinycheek crayfish to the extent that Northern crayfish became the dominant species. 209 Two surveys of Wyoming crayfishes documented the total replacement of the native Pilose crayfish (Pacifasticus gambelii) in the Bear Creek drainage by the Northern crayfish. 116, 117 On the other hand, in some Wisconsin lakes, Rusty crayfish are indirectly replacing Northern crayfish by taking the best cover so that fish can eat more Northern crayfish. 46 One positive impact of this species was noted by in aquaria studies where Northern crayfish were offered zebra mussels and rainbow trout eggs singly and together. When offered only zebra mussels, they ate zebra mussels. When offered both, they preferred the eggs but they did not stop eating zebra mussels. The net food value of mussels was 1/3 that of eggs. 147 Another study used enclosures and exclosures to find that female Northern crayfish ate zebra mussels up to 15 mm and the sizes eaten were directly related to the size of the crayfish. The presence of zebra mussels also reduced predation on snails in the same areas. 186 IMPACTS The Northern crayfish have been introduced into a number of states including Utah 128 , Alabama 228 , Maryland 209 , Arizona 63, 202 , California 200 , Washington 135 , Idaho 27 , New Mexico, Texas, North Carolina, Virginia, Pennsylvania, New York, New Jersey, and West Virginia 253 . In addition, it has been introduced into New Brunswick in Canada 155 , Mexico 21 and Europe 2 . The Spinycheek crayfish, Orconectes limnosus, is native to the eastern seaboard from Maine to Virginia. Within this range, it is rapidly disappearing due to competition with introduced Rusty and Northern crayfish. 139 . DISTRIBUTION AND ABUNDANCE The distribution map shows that this species is widespread throughout the northern U.S. and southern Canada from the Rocky Mountains eastward. In Nebraska it is widespread and common, found in all drainages. It is native to the state with the possible exception of the White River and Hat Creek watersheds in the extreme northwest corner of the state. Streams that have been totally or periodically dewatered, such as Lodgepole Creek, Pumpkin Creek, and Snake Creek in the Panhandle or the Little Blue River have few or no crayfishes anymore. Streams in the south-central and northeast have not been sampled adequately so the Northern crayfish may be more common in these areas than the map indicates. To date, they have not been collected from the Hat Creek drainage. In the White River drainage they are limited to Whitney Lake, Carter P. Johnson Lake and Soldier Creek