7019 - Laserfiche WebLink

Home Browse Search

3 and Vernal, Utah. Other records of Colorado squawfish tagged between 1978 and 1989 probably exist but were unobtainable. An additional unknown number of fish were collected but not tagged after capture and were not included in this study. Capture records of these fish were not well documented and were difficult to verify. Tagging records were assembled into.a. consolidated database. A description of associated problems and recommendations concerning this database are discussed in Appendix A. . Fish were collected from the Colorado, Duchesne, Green, Gunnison, Little Snake, Price, San Juan, White, and Yampa rivers. Gear types included angling, electrofishing, fyke nets, gill nets, trammel nets, and seines. Information documented during capture included river-mile location, habitat identification, and fish measurements. Endangered fishes were tagged under the dorsal fin with either Floy anchor or Carlin dangler tags. Length of each fish was measured to the nearest millimeter (mm) using a standard measuring board with a fixed headpiece (Anderson and Gutreuter 1983). Length was reported as maximum total length (TL). This was measured from anterior margin of snout to tip of the longest caudal fin ray with caudal fin compressed dorso-ventrally (Anderson and Gutreuter 1983). Weights were measured with balance or hanging scales of varying type and capacity. Tagging records were used for analyses of length-frequency distribution, weight-length relation, and growth from recapture records. For most analyses, fish were grouped by river. For weight-length and condition analysis, fish were also grouped by month of capture and maturity stage. Fish were grouped by river because adult fish tend to establish and maintain residency in specific river reaches (Wick et al 1983; Tyus 1990) and should be considered separate stocks (Tyus 1990). This does not imply separate local populations because even though fish over-winter together in the same river reach, they may migrate to and spawn at different spawning locations (Tyus 1990). Only samples from the Colorado, Green, White, and Yampa rivers were sufficiently large to treat separately by river. Records from smaller tributaries with few captures were added to records of each mainstem river. The Price (n=l) and Duchesne (n=20) rivers were combined with the Green River, the Little Snake River (n=l) was combined with the Yampa River, and the Gunnison River (n=27) was combined with the Colorado River. Because water temperature and food availability vary with season and can affect growth, fish were further grouped by month. Mature fish were identified as fish over 428 mm TL. Vanicek and Kramer (1969) found nearly all fish older than age VII (estimated length 454 mm) were sexually mature. Seethaler (1978) macroscopically examined 147 Colorado squawfish between 184 to 652 mm TL. He found that fish longer than 503 mm were sexually mature, and fish less than 428 mm were immature. Of the 34 fish he examined between 428 to 503 mm, 76% were mature. Because so few immature fish were tagged in this study, only mature fish (> 428 mm TL) were used for developing the weight-length relationship and calculating condition. Fish were sexed based on presence of sexual products or secondary sexual characteristics. Because many fishes exhibit sexual dimorphism, fish are usually segregated by sex when calculating weight-length relationships and examining growth rates. Colorado squawfish were difficult to sex based on external characteristics. Because it is an endangered species, individuals were not killed to determine sex; therefore, data grouped by sex were quite limited. Weight-lemzth relationshio The weight-length relationship for most fish is described by the power function: W = aLb , (I) where W equals weight, L equals length, and a (intercept) and b (slope) are constants. H b equals 3, then growth is isometric and shape does not change as length increases. If b does not equal 3, then growth is allometric and shape changes with an increase in length. When b is less than 3, fish become less rotund as length increases. Generally, b is greater than 3, indicating fish become more rotund as length increases. The constants a and b are estimated by taking the log of both