Hamilton Harbour, a semi-enclosed bay located at the western end of Lake Ontario, is listed as one of the most polluted systems in the Great Lakes. Anthropogenic influences such as four wastewater treatment plants, two steel mills and shoreline development have lead to degradation of this system. A Remedial Action Plan is in place to clean up the harbour by 2015. This study examined the food web dynamics of Hamilton Harbour including 21 species of fish, benthic invertebrates, plankton and macrophytes. Using carbon and nitrogen stable isotopes spatial and seasonal variability throughout the harbour was examined. Zooplankton and phytoplankton collected at three different sites in the harbour showed no significant difference spatially but did show seasonal trends, reaching the highest nitrogen values in early summer. Benthic invertebrates, when observed in δ13C: δ15N biplots, group together by sampling site in each season. Seasonally benthic invertebrates acquire higher nitrogen signatures in summer then decrease in fall at all sites. The fish community in the harbour do not have spatially distinct isotope signatures. Seasonally nitrogen signatures increased at all sites while carbon signatures remained between -25 ‰ and -26 ‰. Overall the plankton and benthic invertebrate nitrogen isotope signatures are higher than the fishes. This indicates that there is a recent change in nutrient source. The likely candidate for nutrient input is an anthropogenic source, such as the wastewater treatment plants discharging into the harbour. Isotope signatures show large variation in fish species collected indicating that the fishes are omnivore generalists that take advantage of available food sources throughout the harbour. Further remediation work, such as habitat modifications, can now be tailored towards generalist omnivores that move throughout the harbour.

Hamilton Harbour, a semi-enclosed bay located at the western end of Lake Ontario, is listed as one of the most polluted systems in the Great Lakes. Anthropogenic influences such as four wastewater treatment plants, two steel mills and shoreline development have lead to degradation of this system. A Remedial Action Plan is in place to clean up the harbour by 2015. This study examined the food web dynamics of Hamilton Harbour including 21 species of fish, benthic invertebrates, plankton and macrophytes. Using carbon and nitrogen stable isotopes spatial and seasonal variability throughout the harbour was examined. Zooplankton and phytoplankton collected at three different sites in the harbour showed no significant difference spatially but did show seasonal trends, reaching the highest nitrogen values in early summer. Benthic invertebrates, when observed in δ13C: δ15N biplots, group together by sampling site in each season. Seasonally benthic invertebrates acquire higher nitrogen signatures in summer then decrease in fall at all sites. The fish community in the harbour do not have spatially distinct isotope signatures. Seasonally nitrogen signatures increased at all sites while carbon signatures remained between -25 ‰ and -26 ‰. Overall the plankton and benthic invertebrate nitrogen isotope signatures are higher than the fishes. This indicates that there is a recent change in nutrient source. The likely candidate for nutrient input is an anthropogenic source, such as the wastewater treatment plants discharging into the harbour. Isotope signatures show large variation in fish species collected indicating that the fishes are omnivore generalists that take advantage of available food sources throughout the harbour. Further remediation work, such as habitat modifications, can now be tailored towards generalist omnivores that move throughout the harbour.

Tracking migratory movements of birds between breeding and wintering areas is important for both theoretical and conservation purposes. In particular, information about linkages between stages of the annual cycle (i.e., migratory connectivity) is essential for identifying factors and processes limiting population sizes of birds. Further, this information is necessary for testing assumptions and hypotheses about the evolution of avian migratory patterns. Here, I used stable hydrogen isotope (δD) analyses of tissues representing different periods and geographic regions of the annual cycle of white-throated sparrows, Zonotrichia albicollis, to provide new information on spatial and temporal linkages between stages of the annual cycle of this species. To achieve this objective, I sampled white-throated sparrows during spring and fall migration of 2002 and 2003 at a key staging ground for North American migratory birds located at Delta Marsh, Manitoba. Based on evaluations of the correspondence between δD values of feathers, claws, and cellular portions of blood of migrants, I determined that δD values of claws and blood cells were not suitable for estimating wintering origins of individuals captured en route to breeding areas. However, δD values of head feathers grown on wintering areas and tail feathers grown on breeding areas corresponded to values expected for feathers grown in broad areas within the wintering and breeding range of the species, respectively. The δD values of feathers showed no relationship between estimated breeding or natal and wintering latitudes of white-throated sparrows. However, band-encounter analyses indicated a clear eastwest segregation of populations across Canada, a finding that suggests that this species has a parallel migration system. Temporally, all components of the breeding populations migrated together during spring migration. However, as expected, white-throated sparrows exhibited sex-biased differential timing of spring arrival and latitude of wintering origin. Consistent with several other differential migrants, female white-throated sparrows arrived later and originated from more southern latitudes. There was also a negative relationship between wintering latitude and arrival dates of individuals during the second spring of the study. The existence of this relationship is a key assumption of differential migration hypotheses that had not been previously validated. Furthermore, since timing of arrival at breeding areas is critical to establishing high-quality territories and pair bonds, relationships between wintering latitude and arrival date of individuals could have important carry-over effects to reproduction. Based on standard body condition indices, white-throated sparrows migrating longer distances to reach breeding areas were not in poorer body condition than those migrating shorter distances. Thus, the cost of migrating longer distances does not appear to affect pre-breeding body condition, a parameter known to be linked with reproductive success.

Large rivers in North America have been subjected to a variety of hydrologic alterations that have negatively impacted aquatic fauna. These impacts have triggered restoration efforts, including management of flows, to restore or maintain ecological integrity. Ecological data relevant to flow management and habitat restoration is scarce, and conceptual models of ecosystem function have been widely applied to large rivers despite a lack of quantitative evaluation of these models. Here, I examine demographic and trophic dynamics of fishes with divergent life histories and trophic guilds in relation to habitat heterogeneity and flow variability in a relatively unaltered floodplain system: the Brazos River, Texas. Reproductive activity of fishes with three divergent life history strategies was positively associated with long-term river hydrology, although species with alternate strategies exploited different portions of the hydrograph (peak flow versus increasing flow). Despite the positive association with hydrology, low-flow periods were favorable for recruitment, and food resources for larvae and juveniles were denser during these periods. Some species used both oxbow and channel habitats during some point in their life cycle, whereas other species appeared to be almost entirely restricted to one habitat type. Terrestrial C3 macrophytes accounted for a significant fraction of the biomass of most consumer species examined. Small-bodied species in oxbow lakes assimilated large fractions of biomass from benthic algae, whereas this pattern was not observed in the river channel. Frequent flow variations in the river channel may reduce algal standing stocks, and significant contributions from autochthonous algal sources may only occur during low-flow periods. Trophic positions of detritivores indicated that terrestrial carbon sources were assimilated, for the most part, via invertebrates rather than by direct consumption. My results indicate that current conceptual models are too vague to provide accurate predictions for restoration strategies in rivers with variable flow regimes. Flow and habitat management strategies that focus on reproducing key features of historical fluvial dynamics are likely to be more successful than strategies that focus on single indicator species or flow dynamics that differ from the historical hydrograph.

Thèse doctorat : Océanologie biologique : Brest : 2005. / Bibliogr. p. 277-298.

Thesis--M. Sc., University of Hong Kong. / Typewritten.

Spawning capelin (Mallotus villosus) provide a pulse resource of fish eggs and dead fish on the northeast Newfoundland coast, bringing an abundance of nutrients into the system that can be relied upon by numerous predatory and scavenging species. I investigated how this annual resource pulse influenced the diet and distribution of green sea urchins (Strongylocentrotus droebachiensis) at capelin spawning sites and the potential for urchins to impact capelin recruitment through egg predation. Urchin density was monitored using a remotely operated vehicle (ROV) during the summers of 2013 and 2014, and urchins were collected from capelin spawning sites in 2014 to assess diet using nitrogen and carbon stable isotopes. Urchins were distributed in higher densities in areas with dead capelin and were often clumped directly on dead fish. Conversely, the presence of capelin eggs negatively influenced urchin density. Stable isotope analysis revealed an increase in 15N when capelin resources became available, suggesting urchins were consuming capelin resources. Diet preference experiments also indicated that dead capelin were preferentially consumed over eggs. Overall, urchins appear to prefer and seek out dead capelin on spawning sites suggesting urchins may be important recyclers of capelin detritus and have little impact on capelin recruitment. / October 2015

This thesis is concerned with the measurement and interpretation of isotope shifts. The first part describes an experimental determination of isotope shifts in the 4s^{2 1}S<subo</sub> - 4s5s¹ S_o transition of neutral calcium. This measurement was performed using the method of Doppler-free two-photon absorption spectroscopy in an atomic beam of the natural mixture of calcium isotopes. The laser was stabilized and scanned by means of an external, pressure-swept etalon, and its scan was calibrated by recording the transmission fringes of the laser through a confocal etalon, 2m in length. This calibration etalon was stabilized with reference to an I₂-stabilized Helium- Neon laser. The isotope shifts of all the stable isotopes of calcium were measured; the results are believed to be free from systematic error and so the standard deviations are derived from the scatter of the results. A Isotope Shift ^δv^A-44/MHz 40 -1169.99(28) 42 -563.66(7) 43 -263.67(6) 46 534.34(70) 48 1023.50(7) These results are compared with other accurate measurements of isotope shifts in calcium by laser spectroscopy, by means of the King plot. All the measurements are consistent except for the only odd isotope ⁴³Ca, which, in this transition, unlike those in the other experiments, is free from hyperfine structure. The best values of the isotope shifts are thus determined by a least squares procedure. The mass and field shifts are separated using the values of δ<r²> determined from muonic isotope shifts, and this leads to more accurate values of δ<r²>. The second part of the thesis concerns the interpretation of anomalous isotope shifts in samarium. Pairs of spectral lines had been found for which the shifts of even-even isotopes did not lie on a straight line on a King plot. These deviations are interpreted as evidence for the insufficiency of first-order perturbation theory for the treatment of isotope shifts in a number of levels of the samarium spectrum. By comparing shifts in transitions connecting these levels with shifts in transitions connecting levels for which first-order perturbation theory appears to be a good approximation, values of off-diagonal matrix elements are found. These are not required to be unreasonably large to explain the observed deviations.

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