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59 In Kings Creek, Kansas, the numbers of juvenile Water Nymph crayfish [Note that I consider Water Nymph to be the same as the Northern crayfish] ranged from a low of one per 50 m 2 and up to two per m 2 . Adults were less common and ranged from one per 20 to one per 90 m 2. Mean annual standing crop was 296 mg/m 2 while the mean annual production was 719 mg/m 2 . In simpler terms, the annual production was 2.4 times the standing crop. Most of the production occurred among the smaller crayfishes during the late summer and fall. 55 FEEDING AND SPECIES INTERACTIONS The Northern crayfish, perhaps due to its extensive range within North America, has a large body of literature on its feeding and species interactions. In Kings Creek, Kansas, they consumed leaves (42%), animal matter (16%), filamentous green algae (13%), detritus (23%), and diatoms (6%). Of these, leaves contributed 46% to annual production while animal matter contributed 29%. The animal matter was mostly other crayfish, dragonflies and mayflies. 55 Numerous animals feed on Northern crayfish, so many that a literature review might be several pages long. Suffice it to say that virtually any predator will eat and relish a crayfish. From fishes (bass, trout, etc.) to wading birds (herons) to mammals (raccoons and otters) to reptiles (alligators) up to and including humans. On the other hand, the food of crayfish is almost as extensive. Northern crayfish will eat fish eggs and sac- fry. One study tested the impact of egg predation of Northern crayfish on pumpkinseed (Lepomis gibbosus) and bluegill (Lepomis macrochirus) in ponds. In densely vegetated ponds, pumpkinseed had delayed reproduction and lower young-of- year biomass due to crayfish predation. In less vegetated ponds, crayfish prevented bluegill reproduction except in crayfish- proof exclosures. 50 Another study looked at their impact on lake trout and rainbow trout. While Northern crayfish fed on eggs and sac fry but the overall impact was low in most instances. 204 Northern crayfish can compete directly with adult fishes. In the 1970's, the Northern crayfish appeared in Newcastle Reservoir, Utah, which is a put, grow and take rainbow trout fishery. While the rainbow trout did consume the crayfish, the overall impact was negative as the crayfish competed with the trout for the same food supply. Stocking rates of rainbow trout had to be cut in half to compensate for the reduced food supply and lowered growth rates. 98 The Northern crayfish can alter macroinvertebrate assemblages. In a study where known densities of crayfish and macroinvertebrates were stocking in plastic pools, Northern crayfish greatly reduced the abundance of snails after which the other invertebrates were eaten. This showed that crayfish could substantially impact the macroinvertebrate community and, by extension, the fish community. 87 Northern crayfish can alter plant growth and density. In one study known densities of crayfish were stocked in plastic pools containing four species of aquatic plant (Potamogeton rechardsonii, Myriophyllum exalbescens, Nuphar variegatum and