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<br />the channel plus connectives. Monitoring for <br />parasites, other pathogens, and heavy metals or <br />other contaminants may be incorporated into <br />management protocols as part of the <br />harvest-transfer protocol. If a problem is de- <br />tected, harvest should be increased, though trans- <br />ferring small fish to the channel plus connectives <br />should not be expected to do much more than <br />provide supplemental rations for nonnative <br />predators. <br />To maintain high turnover in parentage, sex- <br />ually mature repatriates should regularly be <br />transferred back into off-channel habitats. Males <br />reach maturity in 2 to 3 years and females in 3 <br />to 4 years (Minckley et al.1991). Replacing 10% <br />of breeding female razorback suckers in off- <br />channel habitats each year results essentially in <br />a complete turnover each decade, which is slightly <br />longer than an estimated generation time of <br />± 7 years. <br />Accommodations for harvest. Other practical <br />problems center on physical capture and trans- <br />fer of fish from isolated backwaters for repatri- <br />ation and of new brood fish from the channel <br />plus connectives back into off-channel habitats to turn over <br />the parental pool. It would be gratifying to produce, for ex- <br />ample, 25,000 or 100,000 fish of appropriate size in isolated <br />backwaters for repatriation, or 40,500 or 162,000 adults in the <br />channel plus connectives after 10 years, but such goals have <br />the potential to be a logistic nightmare involving harvest and <br />transfer. On the other hand, complexities of fish capture, <br />transport, and handling are all surmountable. If serious man- <br />agement is built into water-use infrastructure, a full-time <br />crew with appropriate equipment, training, and incentives can <br />move large numbers of fish, as proved by successful com- <br />mercial fisheries of the past. All four native big-river syeLies <br />in the lower basin are vulnerable to capture, recapture, or other <br />manipulations, in part because of existing knowledge from <br />studies of these species' movements, their habitat use, and <br />other aspects of their biology. <br />Some harvest priorities, such as habitat morphology, may <br />compete with biological requirements. Such conflicts can be <br />resolved using a cost-benefit perspective. Whatever resolution <br />is reached, harvest methods should stress mass collection. <br />Thus, large, smooth-bottomed areas with no obstructions, rel- <br />ative shallowness, and appropriate landing areas should be de- <br />signed for seining. Both razorback sucker and bonytail may <br />show extensive seasonal movement, so movable traps or fixed <br />weirs can be deployed effectively. Electrofishing is especially <br />efficient for subadult and adult Colorado squawfish (Tyus <br />1991), as are entanglement devices such as gill and trammel <br />nets when used by trained personnel. Summer air and water <br />temperatures and chemical conditions can result in elevated <br />mortality, so harvesting should be concentrated in cooler <br />seasons. <br /> <br />40 T (86) (67) (96) (32) (11) (1) (3) <br />E ¦ <br />hJ- 30 ¦ ¦ ¦ <br />c ¦ ¦ <br />Ln ¦ ¦ ¦ <br />20 ¦ ¦ ¦ <br />b ¦ <br />E 10 ¦ <br />3 <br />U <br />1 2 <br />Years after repatriation <br />Figure 8. Growth of cohorts in centimeters (cm) total length (TL) of repatri- <br />ated razorback suckers in Lake Mohave, Arizona and Nevada, based on re- <br />captures of individual fish. Total numbers of fishes in all cohorts for a given <br />year are in parentheses. <br />Cordbct resolubon. Adult native fishes in the channel plus con- <br />nectives are not likely to affect nonnative sport fisheries. <br />The magnitude of ecological saturation by nonnative species <br />in the river channel plus connectives is, however, unknown. <br />If the channel plus connectives are at carrying capacity, food <br />and other resources may be in short supply, and survival of <br />adult natives may suffer. It may thus be necessary to limit the <br />numbers of nonnative fishes to maintain natives at desired <br />densities. Increased public angling pressure might be en- <br />couraged, locally at least, lu reduce population sizes of non- <br />natives, as is being explored in the upper basin (Tyus and <br />Saunders 1996). <br />The success of such efforts can be enhanced by education <br />and by liberalizing angling regulations to ensure sufficient pro- <br />visions for natives. Options should be kept open for other ac- <br />tion, including direct control of nonnatives, especially as fu- <br />ture system modifications for water use reduce the quantity <br />and quality of main channel plus connective habitat. For ex- <br />ample, if water intakes for Las Vegas and coastal California <br />cities were moved upriver, the reduced discharge below Lake <br />Mead would alter downstream conditions dramatically. <br />Because of actual or perceived liability under the ESA, we <br />expect reluctance on the part of water purveyors to accept the <br />presence of large numbers of listed fishes associated with <br />their commodities or facilities developed for water distribu- <br />tion and use. Sport-fish managers will also resist changes <br />that reduce the catch. Further, and from the other side of the <br />issue, strict adherence to ESAs "take" stipulations for listed <br />fishes in the channel plus connectives may, in fact, need re- <br />laxation to apply, assess, and adjust management strategies to <br />ensure their success. <br />March 2003 / Vol. 53 No. 3 • BioScience 231