Michael J. Whitney and Dr. Mark C. Belk, Zoology

We estimated the vulnerability of juvenile June suckers to predation by a growing cohort of juvenile white bass. Also, habitat preference of juvenile white bass (open versus vegetated habitats) in the presence and absence of adult white bass was determined experimentally. Juvenile white bass preferred vegetated habitats similar to juvenile June suckers. June suckers are most vulnerable to juvenile white bass immediately after they hatch and move downstream into Utah Lake. Vulnerability decreases during the summer until by the end of the growing season. Only a small fraction of the juvenile June sucker population is potentially vulnerable to juvenile white bass. These data suggest that addition of vegetation may not be sufficient to significantly decrease the threat of predation to June suckers by juvenile white bass.

The introduction of normative fish species has been a common occurrence in the United States beginning with the introduction of goldfish (Carassius auratus) in the 1600’s. Successfully introduced species are often very adaptable. The adaptive capacity of exotic species often allows them to dominate the new system, especially in communities with low species diversity. Introduction of normative species has been a major problem in the low diversity aquatic systems of the western U.S.

The original ichthyofauna of Utah Lake, Utah, consisted of cutthroat trout, mountain whitefish, Utah chub, least chub, Utah sucker, June sucker, mottled sculpin and Utah lake sculpin (Heckmann et al. 1981). Of these species, only June sucker and Utah sucker survive in the lake. The June sucker is listed as an endangered species. The June sucker is a pelagic fish that migrates into the Provo river to spawn each June. When the adults finish spawning, they return to their lake habitat. The larvae hatch and quickly move down river into the lake. YOY June suckers utilize emergent vegetation as a refuge from predators (U.S. Fish and Wildlife 1995). June suckers probably number less than 1000 and exhibit little recruitment to adulthood (Moode and Muirhead 1994). Lack of recruitment has been blamed on the abundant population of introduced white bass.

White bass were introduced to Utah Lake in 1956 and quickly became a dominant species in the lake (U.S. Fish and Wildlife 1995). Adult white bass are piscivorous and possibly consume juvenile June suckers (Van Den Avyle 1983). YOY white bass consume a variety of prey, but piscivory has been demonstrated (Van Den Avyle 1983; personal observation). Adult white bass avoid emergent vegetation but YOY white bass may use vegetation as a refuge from predators (Petersen 1996). Effects of adult white bass on juvenile June suckers have been studied. However, the potential predation by YOY white bass has not been investigated. In this study, we tested habitat preference of YOY white bass, and we calculated the vulnerability of YOY June suckers to YOY white bass throughout the first growing season, to determine if YOY white bass could be significant predators of YOY June suckers.

We estimated body depth of June suckers through the first summer growing season at ten day intervals using the following data and assumptions. Annual growth of June suckers for the first year was determined from analysis of otolith annuli (lapillus). We assumed growth during the first year occurred primarily during the first summer. We assumed larval June suckers migrate down river on June 20 at a total length of 11.8 mm (Modde an Muirhead 1994; Shirley 1983). We assumed that June suckers grow linearly from hatch until growth ceased when water temperature drops to about 8 C in mid October (Utah Division of Water Quality 1996; Scoppettone 1993). We estimated body depth of June suckers for corresponding total lengths using a regression of total length and body depth measurements from YOY June suckers specimens from the M. L. Bean Museum at Brigham Young University.

We estimated total length of white bass through the first summer growing season at ten day intervals using the following data and assumptions. We estimated total length of white bass by regressing total length on date of capture from samples taken by Utah Division of Wildlife Resources over the last ten years. We assumed linear growth in total length of white bass for their first summer. We estimated mouth gape of white bass for corresponding total length using a regression of total length and mouth gape measurements from YOY white bass specimens from the M. L. Bean Museum, at Brigham Young University. Vulnerability of YOY June suckers to YOY white bass was based on analysis of June sucker body depth and white bass gape according to methods in Hambright et. al., (1991; Fig. 1).

We determined habitat use of YOY white bass in presence and absence of adult white bass using habitat preference experiments in large tanks divided into vegetated and open habitats. We used a one tailed T-test to determine whether the mean number of individuals in the vegetation was greater than the number in the open half .

June suckers hatch at about 11.8 mm in mid-June and grow to an average of 117 mm by the end of the first growing season (Fig. 2). White bass hatch in mid-April at about 2.3 mm and grow to about 131 mm by the end of the first growing season (Heckmann et al. 1981; Yellayi and Kilambi 1970; Fig. 2). Relative vulnerability of June sucker to YOY white bass decreased from 1.00 on June 20 (hatch), to 0.46 thirty days after hatch, and down to 0. 17 sixty days after hatch. Vulnerability remained low for the remainder of the summer (Fig. 3).

YOY white bass showed significant preference for areas of simulated vegetation in the presence and absence of predatory adults. The preference for vegetation by YOY white bass was enhanced in the presence of adults (Fig. 4).

Addition of emergent vegetation to Utah Lake has been proposed as a method to decrease predation by adult white bass on YOY June suckers (U.S. Fish and Wildlife 1995). This study suggests that adding vegetation to Utah Lake may not decrease predation by YOY white bass. Even though adult white bass can consume June suckers over a larger size range, the relatively larger number of juvenile white bass compared to adults, and the similarity in habitat use to juvenile June suckers suggests that juvenile white bass may be a significant source of mortality for June suckers.

Figure 1. Graphical representation of relative vulnerability estimation from Hambright et.al. (1991)

Figure 2. Estimated mean total length (and sd) of white bass and June sucker

Figure 3. Ontogenetic change in relative vulnerability of June suckers to YOY white bass.

Figure 4. Mean number (±2 SE) of YOY white bass (out of five) in vegetation in the presence and absence of adult white bass. Both treatments show significant preference of vegetated habitats.

Literature cited

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• Heckmann, R. A., C. W. Thompson, D. A White. 1981. Fishes of Utah Lake. Great Basin
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• Modde T. and N Muirhead. 1994. Spawning chronology and larval emergence of June sucker (Chasmistes liorus). Great Basin Naturalist 54(4):366-370.
• Petersen, M. E. (1996) The effects of prey growth, physical structure, and piscivore electivity on the relative prey vulnerability of gizzard shad (Dorosoma cepedianum) and June sucker (Chasmistes liorus).Thesis, Utah State University. 55 pp.
• Scoppettone, G. G., M. E. Buettner, and P. H. Rissler. 1993. Effects of four temperature regimes on cui-ui, Chasmistes cujus, survival from egg fertilization to swim-up, and size of larvae produced. Environmental Biology of Fishes 38:373-378.
• Shirley, D. L. 1983. Spawning ecology and larval development of the June sucker. Proceedings of the Bonneville Chapter, American Fisheries Society (1983):18-36.
• U.S. Fish and Wildlife Service. 1995. June sucker (Chasmistes liorus) Recovery Plan. Salt Lake City. Utah. 55pp.
• Van Den Avyle, M. J., B. J. Higginbotham, B. T. James and, F. J. Bulow. 1983. Habitat
  preferences and food habits of young of the year striped bass, white bass and yellow bass in Watts Bar Reservoir, Tennessee. North American Journal of Fisheries Management 3:163-170.
• Yellayi, R. R. and R. V. Kilambi. 1970. Observations on early development of white bass, Roccus chrysops (Rafinesque). Proceedings of the Annual Conference Southeastern Association of Game and Fish Commissioners 23: 261-265.