THE FATE OF BONNEVILLE CISCO EGGS IN BEAR LAKE - EVALUATING MECHANISMS OF EGG LOSS

Bonneville cisco Prosopium gemmifer are endemic to and found only in B ear Lake, Utah-Idaho. As part of an investigation into life history ch aracteristics of this species of special conservation concern, we exam ined survival of Bonneville cisco eggs by measuring changes in egg den sity under natural environmental conditions. Eggs were vacuumed off th e lake bottom over a month period in 1992 and 1993. This survey indica ted that egg loss was high: fewer than 4% of the eggs remained after 3 0 d of an incubation period lasting more than 100 d. Thirty percent of this egg loss could be explained by unsuccessful fertilization or imp roper embryonic development. An exclosure experiment demonstrated, how ever, that the majority of the Bonneville cisco egg loss was due to fi sh predation. A second exclosure experiment indicated that predation r ates were not affected by changes in egg density. Our results suggeste d that fish predation on the eggs may determine recruitment success of Bonneville cisco.