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京都大学 / 新制・課程博士 / 博士(理学) / 甲第23739号 / 理博第4829号 / 新制||理||1690(附属図書館) / 京都大学大学院理学研究科生物科学専攻 / (主査)教授 森 哲, 教授 中川 尚史, 教授 中務 真人 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Potential predation between fishes of recreational interest has incited many bitter conflicts between angler groups. Large predators, such as esocids, are often at the center of these conflicts because of their capacity to alter fish populations. Such a conflict certainly exists between the Muskellunge Esox masquinongy and Smallmouth Bass Micropterus dolomieu fisheries of the New River, Virginia. Following the institution of a 42-in minimum-length limit (MLL) on Muskellunge, bass anglers feared that increased Muskellunge abundance might be negatively affecting Smallmouth Bass via increased predation. In order to ascertain the impacts of the 42-in MLL, I estimated the demographics, abundance, and food habits of Muskellunge combined with bioenergetics modeling to assess changes (i) in the quality of the Muskellunge fishery and (ii) in Muskellunge predation on Smallmouth Bass. Additionally, given the likelihood of future regulations to incite similar concerns from bass anglers, I modeled alternative length-limit regulations (iii) to assess their potential to improve fishery quality, thereby laying the groundwork for managers to address angler concerns before they arise. I found substantial increases in population size structure and in average adult density of Muskellunge since the institution of the 42-in MLL, but bioenergetics modeling did not indicate a notable increase in the consumption of Smallmouth Bass. I also found that high MLLs (e.g., 48-in) were likely to promote the largest increases in trophy production of Muskellunge compared to low MLLs or protected-slot limits (PSLs). This study suggests that the current Muskellunge population likely plays a small role in shaping Smallmouth Bass population dynamics and production in the New River; and lays the groundwork for predicting how the impact of Muskellunge on Smallmouth Bass might change under alternative regulations. / Master of Science

Non-native species richness has been observed to peak at mid-temperate latitudes, shaping a pattern of richness and abundance that is distinct from native species patterns that peak in the tropics. Stronger species interactions, and therefore biotic resistance, may lower invasion success in the tropics and help explain the discrepancy between native and non-native richness and abundance. To test the hypothesis that strong predation and competition in the tropics could limit invasion success, we conducted a distributed experiment on sessile marine invertebrate communities in four regions spanning 47-degrees latitude of the eastern Pacific Ocean. We manipulated predator access and resource availability at 12 sites and sampled experimental communities in early and late stages of assembly. Overall, our results suggest that biogeographic location, assembly timescale, and predation interactively shape invasion success across latitude. Strong predation reduced richness of non-native species in the tropics at both assembly timescales but increased non-native species richness in the subtropics during early assembly. Predation also increased non-native abundance in the tropics by late-stage assembly and shaped non-native composition at both assembly stages. Effects of predation at higher latitudes were weak or undetectable, and increasing resource availability never had a positive impact on non-native richness or abundance at any latitude. Further, non-native richness was greater at early relative to late assembly stages at mid to low latitudes and was consistently low in our high latitude region at both timescales. In a complementary experiment, short-term predator exposure reduced non-native abundance in Panama, further confirming the influence of predation in this tropical region. Our results highlight important biogeographic differences in invasion dynamics and disentangle local mechanisms that can shape regional patterns. / Biology

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In recent years, gull control has become closely tied to seabird restoration in the Gulf of Maine. Herring (Larus argentatus ) and Great Black-backed (L. marinus) gulls are the principal targets of control, yet anecdotal reports suggest that gull predation remains an important source of egg and chick mortality at many managed seabird colonies. The main objective of this study was to examine the impact of gull predation on the reproductive success of several waterbird species nesting at restoration sites in Maine. Particular emphasis was placed on understanding gull foraging behavior, identifying foraging constraints, and applying this knowledge to management of gulls and small seabirds. / Productivity of Common (Sterna hirundo), Arctic ( S. paradisaea), and Roseate (S. dougallii) terns was monitored and daily predation watches were conducted at Eastern Egg Rock, Maine from 2003-2005. In 2004 and 2005 only, attempts were made to shoot gulls preying on terns. Shooting failed to eliminate predation, and tern predation risk was influenced by nest location, but not year. Common and Arctic terns experienced heavy predation in all years, but Roseate Tern nests were seldom depredated, presumably because Roseates selected nest-sites with more cover. Great Black-backed Gull predation was influenced by visibility, tidal state, and year, while Herring Gull predation depended only on the stage of the tern breeding cycle. There was little evidence that gulls preyed selectively on unfit chicks. The limitations of shooting are discussed and non-lethal alternatives suggested. / Common Eider (Somateria mollissima dresseri) nest (hatching) success, habitat use, and duckling survival were studied at Stratton Island, Maine in 2004-2005. Eiders nested in a variety of habitats offering vegetative cover and enjoyed high nest success. Duckling survival was negligible however, because of opportunistic, group attacks by Great Black-backed Gulls. Glossy Ibis (Plegadis falcinellus) also appeared to suffer heavy gull predation, with adults occasionally attacked in flight. In 2006, gull displacement walks, gull nest/egg destruction, and occasional shooting were used on a trial basis and may enhance future eider production.