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<br />12 <br /> <br />sub-adults produced in the backwater (assuming a 1:1, but <br /> <br /> <br />undetermined, sex ratio for recovered young). However, this level <br /> <br /> <br />of production is inadequate to replace the existing adult <br /> <br /> <br />population of about 60, 000 individuals. If 5-10 years is a <br /> <br /> <br />reasonable time frame for complete replacement of the Lake Mohave <br /> <br /> <br />stock (also the span within which the adult population is expected <br /> <br /> <br />to decline to non-sustainable level), then NFWG must find ways to <br /> <br /> <br />annually produce 6,000 to 12,000 sub-adults for augmentation (20 to <br /> <br /> <br />40 times the production achieved in 1992). <br /> <br />Several constraining factors seem especially important, and these <br /> <br />must be dealt with effectively if production is to be substantially <br /> <br /> <br />increased: (1) Space available in the Yuma Cove backwater does not <br /> <br /> <br />appear sufficient to produce target numbers of juvenile fish, <br /> <br /> <br />unless harvest and removal to other locales can be effected at <br /> <br /> <br />smaller sizes before mortality reduces numbers. Additional <br /> <br /> <br />habitats should thus be identified and incorporated into the NFWG <br /> <br /> <br />program. (2) Mortality between hatching and attainment of juvenile <br /> <br /> <br />size probably results in~ the greatest absolute and proportionate <br /> <br /> <br />losses of young fish; mechanisms should be identified and <br /> <br /> <br />implemented to reduce such losses. Further, juvenile mortality <br /> <br /> <br />associated with periods of poor water quality apparently reduced <br /> <br />total numbers by about a third. Capture and handl ing stresses <br /> <br /> <br />likely contributed to this mortality, and sampling should be <br /> <br /> <br />reduced or curtailed when similar conditions occur. If potentially <br />