<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
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