Understanding the Role of Non-Game Fish in Pelican Diet and Distribution at Strawberry Reservoir, UT

Predation and competition are natural ecological processes, though these interactions occasionally cause concern among humans when ecosystem services are involved (e.g., popular fisheries in highly managed systems). The population of American white pelican (Pelecanus erythrorhynchos) at Strawberry Reservoir (Utah) has increased dramatically in the last decade, as have the populations of Utah sucker (Catostomus ardens) and Utah chub (Gila atraria). Anglers and managers are concerned that predation by pelicans and competition from non-game fish species are negatively impacting the reservoir’s prized Bonneville cutthroat trout (Oncorhynchus clarkii utah) fishery. This project focused on non-game fishes and is part of a larger project that examines potential pelican predation on fishes, with an emphasis on cutthroat trout. Our goals included assessing potential for net bias, estimating age-class structure and body condition of non-game fishes, and determining the relative impact pelicans have on the non-game fishes of the reservoir. During the 2014 field season, we caught multiple species of fishes using trap nets and gill nets, measured all captured fishes, conducted counts of the pelican population, and gathered pelican diet samples. Using a Kolmogorov-Smirnov test we determined that gill nets are biased towards larger fishes. Based on length-weight regressions and Fulton’s K factor, we observed higher body condition for Utah chub relative to Utah sucker. By identifying dominant modes of size-frequency distributions and comparing the modes to age-at-length data from previous studies, we estimated that captured Utah chub were age-1 and older, while captured Utah sucker were age-4 and older. We also evaluated the relationships between the number of pelicans and the catch-per-unit-effort of fishes at four different locations in the reservoir, and observed no clear relationship. These results will provide useful information for fish population modeling in the future, for informing the next and final season of field data collection, and for critical management decisions for both birds and fishes in the reservoir