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<br />~, <br />t<1 <br /> <br />,;: <br />" <br />~, <br /> <br />years of age, indicating that these fish were spawned between 1961 and 1975, Adults show little <br />change in length over periods of up to 1 year (Valdez et ai, 1982), or an average of2,2 mmper <br />year for periods of up to 8 years (Tyus 1987). Adults from Lake Mohave show little or no <br />growth for a period of at least 20 years (Minckley et al, 1991), <br /> <br />.. <br />^" <br />~ <br />r~~ <br />,j <br />,~'. <br />~.~ <br />,. <br />;;:... <br /> <br />:{ <br />'. <br />f;, <br /> <br />In contrast to observations of growth of mature adult fish, Bestgen (1990) reported that subadult <br />and young adult razorback suckers showed rapid growth during the first 6 years of life but that <br />growth slowed after that. Laboratory studies (papoulias and Minckley 1990) indicate that food <br />availability and quality are critical to growth and survival of early life stages of razorback suckers, <br /> <br />~, . <br /> <br />V' <br />'-" <br /> <br />c.> <br /> <br />:x <br /> <br />~ <br /> <br />Bestgen (1990) reviewed literature on diets of razorback sucker and found that they varied <br />depending on life stage and habitat occupied, Larval razorback suckers stocked in riverine <br />habitats consumed primarily benthic chironomid larvae. Muth (1995) found that wild spawned <br />riverine larvae also consumed primarily chironomid larvae, Larvae stocked in lentic situations <br />consumed mostly phytoplankton and small zooplankton and fed very little on benthos, The diet of <br />juvenile razorbacks was largely unknown due to scarcity of coUections, <br /> <br />D: <br />i::i. <br />"J' <br />~.f'.:' <br />~ <br />~ <br />ij <br />:'-~ <br />> <br />li.. <br />~_i <br />~{~ <br />~ <br />.,.', <br />,', <br />~:~'- <br />f...;; <br />:",";" <br />j"" <br />kf~. <br />>-:.; <br /> <br />Diet of adult razorback sucker in lacustrine populations were primarily composed of zooplankton <br />and lesser amounts of algae and detritus, suggesting a planktivorus existence with occasional <br />benthic feeding. Adults in riverine populations were primarily benthic feeders, consuming: <br />, <br />ephemeroptera, trichoptera and chironomidae larvae along with algae, detritus and inorganic. <br />material, Diet information recorded for razorback sucker young and adult reflects in large part <br />food items that were commonly available to the populations, . <br /> <br />Para..sites <br /> <br />!:.~.: . <br />.~~~' <br />~ <br />[',;;-:'3 <br />I <br />~,~~ <br />~'i <br />~ <br />'. ~""5 <br />~.. <br />~ <br />I <br />r:~-_i <br /> <br />~:~ <br /> <br />Razorback suckers are commonly infected with an external parasitic copepod (Lemaea <br />cy;prinacea), Flagg (1982) also found a protozoan parasite (Myxobolus sp,) in eye tissue of <br />razorback suckers, possibly leading to blindness in the fish, <br /> <br />Effects or the Proposed ActioD OD the a.zorback Sucker <br /> <br />Large numbers of wild adults 25,000 adults were estimated in 1995 live and breed in Lake <br />Mohave, where a native fish working group is conducting efforts to recover the fish through <br />placing them in predator free grow out ponds areas where fish are allowed to grow large enough <br />to avoid predation. This effort in conjunction with ongoing efforts to establish an upper basin <br />broodstock will preserve the genetic variability of the population until suitable habitat condition <br />allow for successful self sustaining populations in the wild, Razorback sucker observations in <br />Grand Canyon indicate the species may be extirpated. No young or larval razorback suckers <br /> <br />14 <br /> <br />;'1 <br />