Invasive species introductions are associated with negative economic and environmental impacts, including reductions in native species populations. Successful invasive species populations often grow rapidly and a new food web equilibrium is established. Invasive, predatory northern pike (Esox lucius; hereafter pike) were detected in 2010 in Utah Lake, UT, a highly-degraded ecosystem home to the endemic, endangered June sucker (Chasmistes liorus). Here we test whether pike predation could hinder the restoration efforts of June sucker using the number of June sucker consumed by pike at various population densities as our metric. More specifically, we considered pike density at which the population could consume all June sucker stocked a critical threshold. Currently the number of naturally recruited June sucker is drastically lower than the number stocked. Thus, the metric we used to determine whether the pike population could hinder the June sucker restoration efforts is the number of pike that could consume the number of June sucker stocked. We combined pike growth and foraging observations with an energy-budget, bioenergetics consumption model to quantify lake-wide pike predation on June sucker. We also used an age-structured density dependent population model to estimate the pike population growth trajectory under various mitigation scenarios. Of 125 pike, we found an average pike consumes 0.8-1.0% June sucker and 40% sport fish. According to our bioenergetics model simulations, a population of adult pike at a very high density (60 pike per hectare) has the potential to consume nearly 6 million age-0 June sucker per year, which is likely more June sucker consumed than exist in the environment. In addition, our model suggests that an adult pike density greater than 1.5 pike per hectare has the potential to consume all June sucker stocked annually. Our age-structured population model suggests the pike population will reach equilibrium around 2026 at between 8 and 12 adult pike per hectare with the potential to consume between 0.8 and 1.2 million age-0 June sucker per year, respectively. The growing pike population could hamper restoration efforts and threaten endangered June sucker, a population with a mere 2,000 adults, in jeopardy of extinction. Our findings not only inform pike management efforts, but also highlight the importance of allocating resources toward habitat restoration to provide refuge for juvenile June sucker from predation, preventing the spread of aquatic invasive species, and the need for aquatic invasive species education.

The Kittlitz's murrelet (Brachyramphus brevirostris) is a species of conservation concern over the entirety of its known range, which spans coastal Alaska and northeastern Russia. Concerns about the status of the species have been raised due to evidence of population declines in key breeding areas, low reproductive output, and perceived threats to adult survival. A general lack of information related to vital rates and natural history for this species has hampered efforts to address potential threats and drivers of population decline. This thesis addresses the hypothesis that foraging conditions and nutritional stress may be related to the observed low reproductive output and apparent population declines. I used stable isotope analysis of Kittlitz's murrelet feathers and blood to assess foraging habits during four separate periods across the annual cycle. I also used stable isotope signatures (δ¹⁵N and δ¹³C) in feathers from museum specimens collected in southeastern Alaska during 1907–1984 to investigate potential long-term trends in food habits and foraging ecology. I found that δ¹⁵N progressively increased by 5‰ between the vernal pre-alternate molt and the autumnal pre-basic molt, equivalent to an increase of 1.5 trophic levels for assimilated prey, whereas seasonal patterns in δ¹³C suggest shifts in foraging habitat between breeding and non-breeding periods. These results indicate that the pre-breeding diet was comprised primarily of low trophic level prey from offshore habitats, such as macrozooplankton and/or larval fish. During the summer breeding season, Kittlitz's murrelets gradually switched to consuming higher proportions of planktivorous fish from nearshore habitats. By the post-breeding period, during the pre-basic molt, the diet was comprised almost exclusively of higher trophic level prey, presumably forage fish, from offshore habitats. Based on stable isotope signatures of murrelet feathers from museum specimens, these seasonal patterns were evident during the past century (1907-2009). δ¹³C in feathers grown during pre- and post-breeding (pre-alternate and pre-basic molts, respectively) became significantly more depleted over the last century, however, suggesting either a gradual change in diet and/or foraging habitat or a long-term shift in the isotopic composition of prey. I investigated potential energy constraints on reproduction in Kittlitz's murrelets by constructing a bioenergetics model to estimate energy budgets for breeding adult Kittlitz's murrelets under different scenarios of prey energy content and commuting distance between foraging areas and nest sites. Estimated field metabolic rate (FMR) of breeding Kittlitz's murrelets during the chick-rearing period exceeded the hypothetical maximum sustainable working capacity (MSWC; 4 times basal metabolic rate [BMR]) under empirically derived scenarios of prey energy content and commuting distance. This suggests that, under conditions of low energy content in available prey and/or long commuting distances to inland nest sites, Kittlitz's murrelets would be required to expend energy at a rate that, if maintained over an extended period, could be detrimental to subsequent adult survival and overall fitness. In addition, energy expenditure rates at the high end of the estimated range may exceed the rate at which food energy can be assimilated by adult murrelets. Metabolism of fat reserves, as indicated by mass loss during the breeding season, may be a partial, although limited, solution to periods of high energy demand for breeding adults. This thesis research is the first to indicate that Kittlitz's murrelets rely on distinctly different prey resources during different periods of the annual cycle. The previously unappreciated seasonal complexity of Kittlitz's murrelet foraging ecology offers a new perspective on potential factors limiting survival and reproduction in this species of conservation concern. In addition, my research suggests an adaptive explanation for the low breeding frequency and low reproductive output of Kittlitz's murrelets that is related to the exceptionally high energy expenditure rates required to raise young at nest sites as much as 70 km inland from the coast and up to 2,500 m above sea level. Because of their high level of reproductive effort, Kittlitz's murrelets may be more dependent on the high availability of high-lipid marine prey than other seabirds. / Graduation date: 2012