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Federal Register / Vol. 86, No. 1 / Monday, January 4, 2021 / Rules and Regulations
within these tributaries was essential to larval sucker survival and maintaining the species resiliency. Most importantly, slow water pool and marsh habitats provided refuge from predation by larger fishes.
Since European colonization of Utah Valley, changes to the tributaries have decreased the available habitat for June sucker spawning and rearing, although recent restoration projects have improved conditions in the Provo River and Hobble Creek. The Provo River contains many natural characteristics that support the majority of the June sucker spawning run and also play an important role in contributing to the recovery of the species. The Provo River is the largest tributary to the lake in terms of annual flow, width, and watershed area Stamp et al. 2002, p.
19. All of these characteristics contribute to higher numbers of spawning June suckers using the Provo River than the other Utah Lake tributaries. These characteristics also best support the proper timing of the June suckers spawning period and help protect against further hybridization with Utah sucker. Continued increase and improvement of available larval rearing habitat in the Provo River is necessary for recovery of the species.
Biology and Ecology June suckers are highly mobile and can cover large portions of their range in a short period of time Radant and Sakaguchi 1981, p. 7; Buelow 2006, p.
4; Landom et al. 2006, p. 13. Adult June suckers exhibit lake-wide distributional behavior throughout most of the year Buelow 2006. However, in the fall, June suckers congregate along the western lakeshore, and in the winter, move to the eastern areas. One explanation for the easterly orientation in the winter may be the presence of relatively warm fresh-water springs along the eastern shore of Utah Lake SWCA 2002, p. 14.
During pre-spawn staging, in April and May, June suckers congregate in large numbers near the mouths of the Provo River, Hobble Creek, Spanish Fork River, and American Fork River Radant and Hickman 1984, p. 3;
Buelow et al. 2006, p. 4; Hines 2011, p.
8. June suckers generally initiate a spawning migration into Utah Lake tributaries primarily the Provo River, but also Hobble Creek and, to a lesser extent, Spanish Fork River and American Fork River during the second and third weeks of May Radant and Hickman 1984, p. 7. Provo Bay is likely one of their primary pre-spawn and post-spawn congregation areas Buelow 2006, p. 4.

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Most spawning is completed within 58 days. Post-spawning suckers congregate near the mouth of Provo Bay, which could be a response to the high food productivity that remains in the bay until the fall Radant and Shirley 1987, p. 13; Buelow 2006, p. 8.
Zooplankton densities are greater in Provo Bay than in other lake areas Kreitzer et al. 2011, p. 9, providing abundant food to meet the energy demands of post-spawn suckers, as well as an ideal location for the growth and survival of young-of-year June suckers recently emerged from the spawning tributaries Kreitzer et al. 2011, p. 10.
June sucker spawning habitat consists of moderately deep runs and riffles in slow to moderate current with a substrate composed of 48 in 100200
mm coarse gravel or small cobble that is free of silt and algae. Deeper pools adjacent to spawning areas may provide important resting or staging areas Stamp et al. 2002, p. 5.
Under natural conditions, June sucker larvae drift downstream and rear in shallow vegetated habitats near tributary mouths in Utah Lake Modde and Muirhead 1990, pp. 78; Crowl and Thomas 1997, p. 11; Keleher et al. 1998, p. 47. Juvenile June suckers then migrate into Utah Lake and use littoral aquatic vegetation as cover and refuge Crowl and Thomas 1997, p. 11. June sucker juveniles form schools near the water surface, presumably feeding on zooplankton in the shallows. Young-ofyear suckers form shoals aggregations of hundreds of fish near the surface under the cover of aquatic vegetation Billman 2008, p. 3.
However, effects from nonnative common carp, altered tributary flows, lake water level management, nutrient loading, poor water quality, and river channelization have reduced the amount of shallow, warm, and complex vegetated aquatic habitat for rearing at the tributary mouths and Utah Lake interface. This reduction in rearing habitat has reduced survival of June suckers during the early life stages Modde and Muirhead 1990, p. 9; Olsen et al. 2002, p. 6, resulting in reduced population viability and resiliency. As June suckers reach the subadult stage, they begin to move offshore Billman 2005, p. 16.
Species Abundance and Trends Early accounts indicate that Utah Lake supported an enormous population of June suckers Heckmann et al. 1981, p. 8, and was proclaimed the greatest sucker pond in the universe Jordan 1878, p. 2. The first major reductions in the number of June suckers were in the late 1800s. Through the mid-1900s, June
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suckers were caught during their spawning runs and widely used as fertilizer and food Carter 1969, p. 7.
During this period, an estimated 1,653
tons 1,500 metric tons of spawning suckers were killed when 2.1 mi 3.3
km of the Provo River was dewatered due to reduced water availability and high demand Carter 1969, p. 8.
Hundreds of tons of suckers also died when Utah Lake was nearly emptied during a 19321935 drought Tanner 1936, p. 3. After the drought, June sucker populations gradually increased again, but due to the combined impacts of ongoing drought, overexploitation, and habitat destruction, the population did not return to its historical level Heckmann et al. 1981, p. 9. June suckers were rare in monitoring surveys during the 1950s through the 1970s Heckmann et al. 1981, p. 11; Radant and Sakaguchi 1981, p. 5.
By the time the species was listed under the Act 16 U.S.C. 1531 et seq.
in 1986, the June sucker had an estimated wild spawning population of fewer than 1,000 individuals. In 1999, we estimated the wild spawning population to be approximately 300
individuals, with no evidence of wild recruitment Keleher et al. 1998, pp. 12, 53; Service 1999, p. 5.
Due to the immediate threat of June sucker extinction at the time of listing, the UDWR began raising populations in hatcheries and at secure refuge sites.
These efforts resulted in the stocking of June suckers into Utah Lake to boost population numbers beginning in the 1990s and continuing through the present day UDWR 2018b, p. 3. As of 2017, more than 800,000 captive-bred June suckers have been stocked in Utah Lake UDWR 2017b, p. 6. Stocking is planned to continue until the wild population is self-sustaining, which will be determined by population viability analysis JSRIP 2018, p. 10.
Approximately 3,500 June suckers were spawning annually in Utah Lake tributaries as of 2016 Conner and Landom 2018, p. 2. This represents at least a ten-fold increase in spawning fish from when the recovery plan was finalized in 1999 Conner and Landom 2018, p. 2. The vast majority of fish detected spawning in Utah Lake tributaries are stocked fish that have become naturalized survived for multiple years until reaching breeding age UDWR 2018c, p. 7. For all spawning tributaries combined, the spawning population size for both sexes substantially increased from 2008 to 2016, and the total known spawning population size grew by 22 percent.
These figures represent a minimum number of confirmed spawning June
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