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Efforts to reintroduce razorback suckers in the lower Colorado River basin began in 1981 with a memorandum of understanding between the Arizona Game and Fish Department and the US Fish and Wildlife Service (1981-1987 stockings reviewed by Minckley et al. 1991). Similar, but less extensive, reintroduction programs have been conducted by the states of California and New Mexico. In addition, some partnership programs have emerged such as the Lake Havasu Fisheries Improvement Program, which has agreed to release 30,000 sub-adult razorback sucker into Lake Havasu by the year 2003 (J. Provencio, U.S. Bureau of Land Management, pers. comm. 1998). Reintroduction efforts began during the 1980s when over 12 million small razorback suckers were stocked in the rivers of the lower basin (Mueller 1998). Very few of these stocked fish were recaptured in subsequent years, despite considerable monitoring effort. Because survival of young fish was very low (Minckley et al. 1991), recent stocking efforts have used larger razorback suckers. The most extensive razorback sucker augmentation effort now in progress is in Lake Mojave (summarized by Mueller 1995, 1997). Biologists are rearing the larval fish captured from lakeside backwaters of Lake Mojave and returning the larger juveniles back into the lake. About 15,000 of these "repatriated" juvenile razorbacks have been stocked in Lake Mojave since 1992. Annual monitoring has indicated that recaptures of repatriates ranges from a "few" to nearly half of all the razorback suckers captured, and ripe fish of both sexes have been recaptured on spawning grounds in the lake (P. Marsh, personal communication 1998). Although razorback suckers also have been reintroduced in Lake Havasu, reintroduction efforts there have been hampered by poor survival of the fish (i.e., 0.005%) in grow out facilities (Doelker and Conner 1998). A total of 2,360 razorback suckers were released into Lake Havasu from 1994 to 1997 (Doelker and Connor 1998). The behavior and habitat use of hatchery-reared razorback suckers reintroduced into various locations have been monitored by biotelemetry. This includes studies in lakes Mohave and Powell where many of the fish have survived for over one year (e.g., Mueller 1998). Hatchery-reared razorbacks also have been radiotracked in the Gila and Verde rivers, but none of those fish survived over a year (P.B. Marsh, pers. comm. 1996; Creef and Clarkson 1993). Survival of reintroduced fish in the San Juan River has been more successful and razorback suckers there have survived for at least two years (Ryden and Pfeifer 1995). Augmentation plans have been developed recently for various locations in the upper Colorado River Basin (e.g., Modde et al. 1995, Kesler 1997). Critical Habitat A central feature of the recovery program for the razorback sucker is the designation and protection of critical habitat. Critical habitat (defined in section 3[5][A] of the Act) includes locations within the geographical area occupied by the species that contain physical or biological features essential to the conservation of the species, and that may require special management considerations or protection. Critical habitat may also 26