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adults. Although we offer a rough outline below, development of a captive broodstock will by necessity need to be an adaptive management process. An appropriate broodstock for humpback chub might entail holding up to several thousand fish. Although a minimum of 50 to 500 genetically effective founding breeders has been recommended in the past for brood stock development, genetics theory indicates that these numbers are too low for maintaining quantitative variability (Lande and Barrowclough 1987, Lynch et al. 1995, Lande 1995). For example, Lynch et al. (1995) suggests maintaining long term population sizes> 1,000 in order to avoid problems with mutation loads, and Lande (1995) suggested that the Franklin-Soule number (Ne = 500) should be increased by a factor of ten, to Ne = 5,000. A potential source of broodstock is the -80 humpback chub currently held at Willow Beach NFH. During July 1998, -450 age-O humpback chub were removed the LCR, and flown to Willow Beach NFH for use in temperature growth studies (Gorman and VanHoosen 2000). About 80 of these fish remain. Although these fish came from the LCR, they were never intended to form the nucleus of a breeding program. They were all collected during a single day within a short reach of the LCR (10 to 12 km), and may not fully reflect the genetic variability in the population as a whole. Developing the genetic "fingerprint" of these fish and comparing it with reference samples from throughout Grand Canyon would be absolutely necessary (see Appendix 1). It has been suggested by some to remove the small mainstem aggregation of humpback chub from the Fence Fault area (near river mile [RM] 30). This aggregation is suspected of being a last remnant of the mainstem spawners in Grand Canyon, but recruitment is likely absent (Valdez and Masslich 1999). Based on multiple mark- recaptures, the small aggregate is thought to be comprised of about 50 adult fish (Valdez and Masslich 1999). However, until genetic analyses indicate that these fish are not distinct from LCR fish, these fish may have to be maintained as a separate brood stock in order to avoid potentially swamping this presumed mainstem genotype with the LCR genotype. It should also be mentioned that there has been documented movement of fish between 30-mile and LCR, indicating that these fish are not totally isolated. Without substantive genetic information, removal of fish from 30-mile may only serve to needlessly extinguish this group of fish from the wild. An alternative to capturing the last remaining adults at 30-mile might be collecting eggs or age-O from this group of fish (B. Persons, Arizona Game and Fish Department). Post-larval humpback chub have been captured at the spring at 30-mile (Valdez and Masslich 1999), but successful collection may require stabilization of flows from Glen Canyon Dam during the months of June and July. The strategy involved in using either the Willow Beach NFH or the 30-mile aggregation as a starting point for developing a captive broodstock entails 1) determine the genetic constitution of the original group(s) of captive fish 2) compare these respective small captive populations with the respective genetic constitution of the wild population(s) in the LCR or Grand Canyon, and 3) develop methodologies to ensure that the genetic constitutions of the original captive fish come to equal those of the wild population(s). 18