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seining hauls were made in each backwater, and one similar haul was made <br />along the adjacent river shoreline. The relative abundance of ea~h <br />species within samples was calculated as the number of fish perm swept <br />by seines. Relative-abundance data for each species were averaged <br />within 10-mile river reaches which correlated with earlier larval work. <br />Data from seining in backwaters and along adjacent shoreline areas were <br />treated separately when pooled averages were calculated. <br />Humpback and roundtail chub <br />Humpback chub, roundtail chub and the presumed intergrades of these <br />species were collected about weekly from the Black Rocks area between <br />April and July, 1983. Trammel nets were the principal fishing gear but <br />angling was used when the debris-laden waters of spring and early summer <br />precluded the use of nets, Each Gila specimen was weighed (g) and <br />measured to total and fork lengths (mm). External characteristics of <br />seasonal reproductive development -- flowing ova or milt and the presence <br />of nuptial tubercles -- *aere recorded. Relative, body condition (K ) was <br />c alculated for each ,fish using total length, and gonadosomatic ind~ces <br />(gonad weight '100/whole-body we fight) and mean ovum diameters used to <br />estimate spawning times. The occurrence of expressable ova or milt, the <br />presence of nuptial tubercles, and K were later compared to gonado- <br />somatic indices and mean ovum diameters to determine which of these <br />former, non-lethal measurements might be useful indicators of the time <br />of spawning. Humpback chub not used for gonad studies were given a <br />numbered Carlin Dangler tag prior to their release. <br />We also used radiotelemetry to help identify spawning areas for humpback <br />chub. Radio transmitters, which weighed about- 9 g (in air) and had a <br />battery life of about 90 days, were su rgically implanted in matu re fish. <br />Ten humpback chub were implanted with radio transmitters and released at <br />their capture locations between early April and early May, 1983 (Table <br />1). Searches for these radiotagged fish in the Black Rocks river reach <br />and in the adjacent upstream and downstream river reaches were made <br />weekly, concurrent with netting and angling efforts. <br />Backwater and Gravel Pit Investigations in the Colorado River <br />Biological sampling of selected gravel pits adjacent to the Colorad o <br />River was performed using trammel nets and seines during daylight (3x5 <br />m~mesh), electrofishing during darkness. In addition, qualitative <br />sampling for larval fishes was conducted with a fine-mesh hand net. <br />• The biological sampling program for river backwaters differed somewhat <br />from that for gravel pits. Because river backwaters used by young <br />Colorado squawfish in the Colorado River normally contain too few Colorado <br />squawf fish for a study of the interactions of these fishes and their <br />environment, the natural Colorado squawfish populations in .study backwaters <br />were supplemented using fish raised at Dexter (New Mexico) National Fish <br />7 <br />