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<br />associated with environmental and demographic variability, and scale collection should be <br />representative of fish sampling so that relevant, unbiased conclusions can be made about the <br />Colorado and Green river systems. Also, laboratory and field experiments to determine intensity <br />and interaction of mechanisms of overwinter selection would provide insight into age-O <br />recruitment limitations. Such experiments are currently occurring for age-O Colorado <br />pikeminnow in the San Juan River where age-O fish are being stocked into the river at varying <br />lengths, times and sites, and growth and survival are being evaluated (Lentsch et al. 1996), In <br />addition, backwater habitat quantity and quality and their effect on fitness of age-O fish is being <br />compared to determine differences in physical, chemical or biological characteristics that might <br />explain differences in year class size and length and overwinter survival in different areas. <br /> <br />RECOMMENDATIONS <br /> <br />1) Scale collection become a part ofISMP sampling to some extent. <br /> <br />2) Less than 9 circuli be used as the criterion for fish that formed a first year growth check <br />to ensure more accurate aging. <br /> <br />3) Laboratory and field enclosure experiments should be conducted to quantitatively <br />evaluate factors limiting recruitment (biotic v. abiotic) of age-O Colorado pikeminnow in <br />summer and fall (e.g. spawning success and larval recruitment). <br /> <br />Authors Note: <br />Although many of these types of ecological studies have been ongoing, often with less <br />than conclusive results, it is the valuable information from these studies that will allow us <br />to narrow down and pinpoint factors limiting recruitment so that recommendations for <br />more on the ground projects (e.g. dam operations and habitat or nonnative manipulations) <br />can be effectively (financially and logistically) directed. <br /> <br />14 <br />