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J an uary 1988 TYUS, MINCKLEY: MORMON CRICKETS 27 TABLE 1. Numbers of fish captured using Mormon cricket, Anabrus simplex, as bait or fish whose stomachs contained crickets. All fish were captured in DNM 1986-1987 ([-] indicates no records kept). N umber of individuals Family Species Status 1986 1987 Cyprinidae Cyprinus carpio introduced 2 12 . Gila cypha endemic 16 29 J Gila robusta endemic 134 185 Ptychocheilus lucius endemic 1 3 Catostomidae Catostomus latipinnis endemic 1 9 Ictaluridae Ameiurus melas introduced 8 Ictalurus punctatus introduced 161 Salmonidae Salmo clarki introduced 0 1 Salmo gairdneri introduced 0 4 Salmo trutta introduced 0 20 Cottidae Cottus bairdi native 0 1 .. roads in early May, and huge bands of late ins tars and adults migrated into river canyons in early June through July, All Mormon crick- ets observed encountering streams ultimately entered the water; we saw no individual turn from the water's edge for more than a few minutes. Crickets entrained in river currents varied from a few individuals per hour to con- centrations of over 50 individuals/mz of water surface, Entrained crickets remained on the surface and continued to swim for long peri- ods, Live, moribund, and dead individuals accumulated in eddies and remained at or near the surface for hours, Downstream from shorelines where migrating bands were enter- ing the river, numbers averaged 10-20 indi- viduals/mz, Largest numbers were observed where a tributary creek intersected a migra- tion and carried the crickets in large numbers to the mainstream, In this instance, 50 indi- viduals/mz is a conservative estimate, Highest numbers were observed in eddies where crickets accumulated. In such instances, their abundance exceeded the last value, and, in minutes, hundreds of crickets climbed aboard our rafts. A total of 430 Mormon crickets were weighed from 12 collections taken in 1987, Average weight per cricket was 3,03 g, A sub- sample of 112 males averaged 2,84 g (range 2,30-3,02 g), and 141 females averaged 3, 12 g (range 3,07-3,27 g), Although we could not reliably estimate the biomass of crickets, we observed several bands of 1 kmz or more en- tering the Green River. At 10-20 individuals/ mZ, one of these bands could weigh 30-60 metric tons. Eleven fish species, in five families (Table 1), fed on Mormon crickets from 18 May to 1 August 1987. A total of587 fish were captured by angling in 1986 and 1987 with Mormon crickets as bait, or had crickets in their diges- tive systems, Included were four endemic Colorado River fishes: round tail chub, Gila robusta; humpback chub, Gila cypha; Colo- rado squawfish, Ptychocheilus lucius; and flannelmouth sucker, Catostomus latipinnis, Roundtail chub and the endangered hump- back chub were voracious feeders on Mormon crickets, Although bait records for 1986 were incomplete, these two species comprised 53% (N = 210) of fish captured in 1987 (N = 399) with cricket-baited hooks (Table 1). Three Colorado squawfish were captured using crickets for bait, and a fourth attempted to eat a cricket but was not landed, When Mormon crickets were present, all fish species large enough to eat them had done so, Small individuals of aggressive, omnivo- rous species (channel catfish, Ictalurus punc- tatus, and black bullhead, Ameiurus melas) dismembered and devoured even the largest crickets, Remarkable numbers were present in some digestive tracts, distending stomachs and intestines and, in some cases, filling buc- cal cavities and protruding from mouths, Channel catfish and carp (Cyprinus carpio) were observed at the water surface feeding on crickets in eddies whenever crickets were present. The most striking example of point input and opportunistic feeding was observed 28 May 1987 at the confluence of the Green River and a small tributary in DNM, Nine- teen of 21 brown trout (Salmo trutta), 1 of 3 rainbow trout (Salmo gairdneri), and 1 cut- throat trout (Salmo clarki) taken immediately below the inflow were gorged with crickets, However, no Mormon crickets were observed