• Biotic and abiotic influences on the use of Arctic lakes by fish and loons

      Haynes, Trevor B.; Lindberg, Mark; Rosenberger, Amanda; Lopez, Andrés; Titus, Kimberly (2014-12)
      The particularly severe effects of climate change anticipated in the Arctic, accompanied by ongoing anthropogenic activities, necessitate proactive and knowledge-based management of the region's aquatic ecosystems. However, the paucity of information on the Arctic's aquatic environments hinders strategic or spatially-explicit management. In this dissertation, I examine the habitat use of poorly studied taxa of the Arctic Coastal Plain (ACP) of Alaska, including freshwater fishes and yellow-billed loons (Gavia adamsii). Distribution studies can be biased by false absences; therefore, I began by determining the detection probabilities of six fish species common to Arctic lakes for five gear types (Chapter 2). Variation in gear- and species-specific detection probability was considerable, suggesting a multi-method approach may be most effective for whole-assemblage sampling. Adjusting for detection probability, I then examine how occupancy probabilities of the six fish species were related to lake and landscape scale covariates (Chapter 3). Three large-bodied salmonid species were influenced by factors associated with the probability of fish colonizing lakes, including whether the lakes had a stream connection. Models for small-bodied fish indicated different strategies for persistence among species. Ninespine stickleback (Pungitius pungitius) were widespread and captured in lakes that freeze to the bottom, suggesting rapid dispersal after spring freshet (when snow and ice had melted rapidly and caused widespread flooding) and colonization of sink habitats. In contrast, Alaska blackfish (Dallia pectoralis) distributions reflect tolerance to harsh conditions, while the slimy sculpin's (Cottus cognatus) was indicative of its marine origin. Based on these patterns, I propose a model of primary controls on the distribution of fishes in ACP lakes. Severe winter conditions limit occupancy through extinction events, while lake occupancy in spring and summer is driven by directional migration (large-bodied species) and undirected dispersal (small-bodied species). To provide insight to the relevance of species-specific distributions of prey fish to yellow-billed loons (Gavia adamsii), I investigated loon diet on their breeding grounds using quantitative fatty acid signature analysis (Chapter 4). Tissues were collected from 26 yellow-billed loons (shortly after they had moved from coastal staging areas), nine fish species and two invertebrate groups. Results suggest that yellow-billed loons are eating high proportions of Alaska blackfish, broad whitefish (Coregonus nasus) and three-spined stickleback (Gasterosteus aculeatus). The prominence of blackfish in diets highlights the importance of this species' tolerance to winter conditions that permits its widespread availability during the early stages of loon nesting. Broad whitefish and three-spined stickleback are more likely to be encountered in coastal regions at this time, and their importance may reflect pre-nesting period diet, when loons are staging in coastal and brackish waters before lakes are ice free. Finally, I use the prior chapters to inform an investigation into lake occupancy dynamics of nesting yellowbilled loons and loon chicks (Chapter 5). From a total of four years of data (collected over nine years for nests and seven years for chicks), I examine landscape features that influence the distribution and breeding success of breeding loons on ACP lakes (>7 ha in area), including landscape and lake features, and fish prey occupancy. Over this time, nesting yellow-billed loons exhibited a relatively low (< 30%), but stable to increasing, lake occupancy. Local extinction and colonization rates were also relatively stable, suggesting the nesting population in this region may be near equilibrium. A decreasing rate of change in chick occupancy associated with concomitant increases in nesting occupancy implies density-dependence in chick production. The occupancy probability of a prey fish, least cisco (Coregonus sardinella), had a positive influence on the probability of colonization of unoccupied lakes by nesting loons. I confirm that lake size and lake depth were not only positively associated with nesting occupancy, but also with chick production. Large lakes had occupancy probabilities near one for nesting loons and chicks; this, along with the near equilibrium in breeding loon occupancy and the relative rarity of these large lakes over the landscape, suggests breeding habitat is limiting loon populations in this part of their range. Given the lack of data from the ACP on fish distributions and yellow-billed loons, my findings inform current management practices and provide foundation for future research.