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-3- <br />Development within the floodpl.ain and increased water demands <br />have led to channelization projects which have further modified <br />the physical nature of the River (Beland 1953). Limnological data <br />obtained in the lower River indicate that the chain of large <br />storage reservoirs has had a dramatic chemical and biological <br />effect (L. Paulson pers. commun.). <br />During the past 10 years, fishery surveys on the lower <br />Colorado River have concentrated on exotic gamefish populations <br />and, although a few razorback suckers have been reported, these <br />surveys may not have accurately expressed the representation of <br />this species in the fishery. Turbulent laminar flows, eddies, <br />organic drift, submersed.objects, shifting substrates and high <br />conductivities are all problems to most active and passive fish <br />survey techniques and can.result in poor representation of the <br />fish species present. Routine sampling by-fish and game agencies <br />in the 3 to 5 years prior to.this survey failed to document the <br />presence of razorbacks anywhere on the lower Colorado River except <br />Senator Wash Reservoir (Imperial County, CA). Adult numbers there <br />were estimated at less than 200 in 1981. <br />Recent studies of.daily and seasonal movement patterns, <br />preferred spawning substrate and reproductive behavior of <br />razorback suckers at Senator Wash Reservoir indicate that both <br />male_and female adult suckers spend a significant percentage of <br />time from January through March on or neer (and return to) defined <br />shallow spawning areas. Substrate composition, slope and water <br />