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1 1 ~.. Enhancement offish populations through- stocking has taken place for decades and in recent years has included listed species, the most obvious being members of the Family Salmonidae. However, these actions have not always been in the best interest of the species and fish culture experts have recognized for over a century that hatchery raised fish have certain behavioral deficits that result in poor survival rates in the wild (Brown and Day 2002). Recently, three principal management techniques have been proposed to increase .survival rates of stocked fish thus leading to persistence and. their possible recovery. These management techniques include: environmental enrichment, life-skills training, and hard vs soft release (Brown and Day 2002). Environmental enrichment includes increasing the structural diversity of the rearing site. Fish should be raised in a more natural area (pond) or structures should be added in the hatchery. Life-skills training involves exposure to prey and potential predators. Hard release is the practice of immediately releasing fish into a habitat without prior conditioning to that habitat. Soft release enables the fish to become accustomed to the prevailing environmental conditions, familiarize themselves with the habitat, recover from the stress of transport (both physiological and from transport chemicals), and evade potential avian and aquatic predators. Researchers have shown that fish raised in a lentic habitat and exposed to current prior to release, are better conditioned to flowing water and are better able to survive (Mueller and Marsh 1998; Mueller et al. 1999).. Factors such as site of release, time of day/year, size at stocking, and stocking procedure (en masse or in small groups) all have impacts, which need to be determined for "big-river" fishes. Preliminary studies have illustrated less erratic behavior in razorback suckers that were held for several days prior to release vs razorback suckers that were "hard released" (Mueller 2000, Mueller et al. 2003). It is also known that razorback sucker <30 cm exhibit little or no return to the creel; hence fish >30 cm are stocked (Marsh 1999). Surprisingly, the time needed to change the behavior of a species is short, taking less than a week, and in some cases only a few hours of conditioning have a significant effect on survivability (Brown and Day 2002). GRAND CANYON SUBUNIT MANAGEMENT PLAN SUBUNITS Background Information 13