1,721,098 research outputs found
Food web metrics of piscivorous predators in the Lake-Huron Erie Corridor using stable isotopes
Full text linkThe Laurentian Great Lakes are home to a high biodiversity of freshwater piscivorous predators; however the trophic role of these species is poorly understood. Using stable isotopes of carbon (δ13C) and nitrogen (δ15N), I examined trophic position, niche widths and overlap of piscivorous predators across three sites in the Lake Huron-Erie Corridor (HEC). Trophic position (TP) was determined by δ15N, while habitat utilization was measured using δ13C. Across all sites and species, mean trophic position ranged from 4.0 to 5.1, were highest for Longnose Gar (Lepisoteus osseus), and lowest for Northern Pike (Esox lucius). Bowfin (Amia calva) had a larger niche width and low overlap with other predators across site, while Longnose Gar and Northern Pike had the smallest niche widths and high interspecific overlap. Variation in TP, niche width and overlap suggested different foraging behaviour, trophic interactions, and more complex food web structure in the HEC than previously believed
Comparative analysis of organochlorine accumulation in two top predator shark species with contrasting life history traits
Full text linkSharks vary widely in life-history strategies, and possess unique lipid metabolism. Because of this diversity, and organochlorine (OC) lipid association, dynamics of OC accumulation in elasmobranch-rich ecosystems may be ineffectively predicted by the typically relied upon indicators, stable isotopes and body size. I compared ontogenetic OC profiles and concentrations between dusky ( Carcharhinus obscurus ) and white ( Carcharodon carcharias ) sharks. OC concentrations were elevated in the larger, higher trophic position (TP) white shark, but despite a tenably faster growth rate, ontogenetic diet shifts to mammal prey, and regional endothermy, slopes of growth-dilution corrected concentrations with age were equal between species. Similar ontogenetic TP increases, infrequent white shark seal predation, or inaccurate growth parameters are possible explanations. Inshore habitat use and mass varied in white and dusky sharks respectively with OC profiles and concentrations. TP and mass predicted interspecific concentrations and may therefore be considered reliable indicators of OC accumulation in these sharks
Predicting spread of the invasive macrophyte Cabomba caroliniana in Ontario
Full text linkHumans play a major role in the global spread of nonindigenous species (NIS). Predicting spread of NIS requires an understanding of where propagules are being transported, whether these propagules can survive in novel habitats and whether they can integrate successfully within the recipient community. 'Cabomba caroliniana' is an aquatic plant, native to South America that is now widespread globally. This study is the first attempt to model a macrophyte species using a combination of passive and active dispersal models coupled with an environmental suitability component to measure the first two stages of the invasion process - introduction effort and environmental tolerance - to forecast 'Cabomba' spread in Ontario. Results indicate that Rice, Scugog and Round Lakes have the greatest invasion risk by 'Cabomba' due to the combination of boater and water movement and lake suitability. The best predictors of lake suitability were pH, mean lake temperature and dissolved calcium, respectively
An Integrative Approach to Examining the Trophic Ecology of a Common Benthic Fish in the High Arctic
Full text linkShorthorn Sculpin (Myoxocephalus scorpius) are a common fish in the Arctic that congregate in large numbers in nearshore areas during open water periods, yet little is known about their role in arctic food webs relative to other common consumers like Arctic Cod (Boreogadus saida). This study made use of stable isotope and stomach content analysis as well as acoustic telemetry to examine prey selection, diet specialization, trophic position/coupling, and movement patterns. The influence of Arctic Cod presence was also examined. Results indicate that Sculpin trophic ecology changes with total length and prey availability. Distinct movement patterns were identified that potentially represent different foraging behaviours. Sculpin changed movement patterns in the presence of high abundances of Cod, and two Cod were found in Sculpin stomachs. However, data suggests that Shorthorn Sculpin trophic ecology and movement patterns are more heavily influenced by other prey and changes in abiotic variables
Spatial, temporal and within-species variation in the foraging ecology of a marine predator across a dynamic seascape
Full text linkSpatial, temporal and within-species variation in the foraging ecology among consumers add to the complexities of trophic structure and its processes across all biomes on Earth. In this dissertation, I investigated the foraging ecology and plasticity of an ice-adapted marine predator, the ringed seal (Pusa hispida), inhabiting the Arctic marine environment – a dynamic seascape undergoing rapid climatic changes – across age, space and time using stable isotope analysis and animal satellite telemetry. I used a long-term dataset (1990 – 2013) of ringed seal muscle (n = 630) and liver (n = 558) samples, as well as satellite telemetry data (1999-2013; n= 132) collected from seven locations across the Arctic of varying latitude (56ºN – 76ºN) and longitude (-117ºW – -61ºW). I first quantified the general increase in δ13C and δ15N values of three tissues from eight arctic marine mammal species after chemical lipid extraction with results varying across species, developed species- and tissue-specific lipid normalization models, and a species-tissue-specific decision framework for the best lipid correction approach. I then quantified spatial and temporal variation of ringed seal dietary prey contributions, isotopic niche size and trophic position during ontogeny across the Arctic. I found a general latitudinal trend where the level of fish consumption and trophic position of ringed seals decreased due to increased prevalence of sub-arctic fish species and less trophic complexity in the zooplankton community at lower latitudes. As well, isotopic niche size for ringed seals and beluga whales (Delphinapterus leucas) increased at lower latitudes and level of individual specialization in ringed seals increased at lower latitudes as a response to large-scale spatial variation in ecological opportunity (i.e. prey species richness) which is higher at lower latitudes. Using satellite telemetry, I found that individuals from higher latitudes, which undergo shorter ice-free seasons, spend more time traveling and less time foraging than individuals from lower latitudes where the ice-free season is longer. Also, smaller individuals spent more time transiting between habitat patches than their larger conspecifics due to competitive exclusion. Overall, these findings highlight the foraging plasticity of ringed seals to changing environmental conditions and resource availability
Acoustic telemetry in freshwater habitats: the influence of macrophytes on acoustic transmitter detection efficiency and identifying predation using novel transmitters
Full text linkAcoustic telemetry is a popular tool to study the movements of animals and has resulted in substantial ecological knowledge gain. To effectively carry out acoustic telemetry studies, many technical and biological considerations must be made. This thesis aimed to fill gaps in knowledge pertaining to two common considerations in passive acoustic telemetry studies, particularly in nearshore freshwater habitats: understanding the influence of macrophytes on the detection efficiency and range of acoustic telemetry equipment and identifying whether or not tagged animals have been consumed by an aquatic predator. Through the application of detection range testing and hydroacoustic surveys, it was revealed that distance and macrophyte biovolume interact to significantly influence the detection efficiency of acoustic transmitters, and this influence varied significantly based on the seasonal growth and senescence of macrophytes. The distance at which 50% of transmissions were successfully detected ranged from 5.5 m (± 139.6 S.D.) to 186.8 m (± 114.4 S.D.) and was significantly correlated to seasonal fluctuations in macrophyte biovolume. One of the first field applications of novel transmitters that identify predation events of tagged individuals indicated that 31.7% of tagged fish (n = 60) were apparently predated, and variable detection patterns were demonstrated using spatial metrices to examine the transmitter movements before and after the apparent predation event. The novel information presented in this thesis regarding the significant seasonal influence of macrophytes on detection efficiency and range and the application of acoustic transmitters that identify predation events in the wild will inform and improve future acoustic telemetry studies
Implications of Developing Deep-Sea Arctic Fisheries for Greenland Halibut (Reinhardtius hippoglossoides): Inshore Stock Connectivity and Capture Induced Stress of Ecologically Important Fish Species
Full text linkOne of the most pressing issues facing developing Arctic fisheries is a lack of scientific knowledge available to inform management. This thesis develops two key ideas essential to establishing a sustainable harvest of Greenland Halibut (Reinhardtius hippoglossoides) within Scott Inlet, Baffin Island: inshore/offshore connectivity of Greenland Halibut stocks, and capture induced stress of Greenland Halibut and Greenland Shark (Somniosus microcephalus). The majority of Greenland Halibut only utilised the inshore environment during the summer, ice-free, season spending about 27±14 days within the system before exiting offshore. A small resident portion of fish, spent on average 261±79 days within Scott Inlet throughout the year. Capture stress indicated that undersized Greenland Halibut do not express greater physiological perturbations, yet Greenland Sharks captured at greater depths had higher lactate values (300-600 m: 1.6±0.5 mmol/L and 700-900 m: 3.7±1.2 mmol/L). This information will contribute to the sustainable development of Greenland Halibut fisheries in the Arctic
Diet reconstruction and niche of Lake Ontario top predators and corresponding prey species
Full text linkLake Ontario supports a diverse offshore fish community consisting of salmonids and forage fish with little known about the resource partitioning and habitat use of these species. To assess this, I used stable isotopes to determine the isotopic trends (forage fishes only), niche structure and overlap of both salmonids and forage fishes. I also estimated the salmonid trophic position (TP) and diet using stable isotopes. Forage fishes had high resource partitioning but was low between Myoxocephalus thompsonii and Cottus cognatus. Regional and temporal discrete subpopulations driven largely by nitrogen were only present in Alosa pseudoharengus, Osmerus mordax and Neogobius melanostomus. Salmonids had low resource partitioning, particularly Oncorhynchus tshawytscha and inhabit the offshore. A. pseudoharengus comprised a major proportion of the salmonid diet, followed by N. melanostomus while Salvelinus namaycush had the highest TP. Salmo salar restoration may prove difficult to due to high isotopic and diet overlap with other salmonids
Addressing Data Deficiencies in a Threatened Mobile Marine Predator
No full textKnowledge of ecological and life-history traits over ontogeny for long-lived migratory marine species is vital to creating effective conservation and management strategies, however these details are often difficult to obtain. Incrementally growing biomineralized structures, such as elasmobranch vertebrae, are metabolically stable and provide the potential to investigate changes in spatial and trophic ecology over ontogeny. In the present dissertation, chemical tracer analysis (δ13C, δ15N, and Δ14C) and opportunistic sightings data are used to address data deficiencies for a threatened marine predator (white shark, Carcharodon carcharias)
Effects of acoustic telemetry transmitter implantation on survival, growth, resting metabolic rate, and swimming performance in juvenile rainbow trout (Oncorhynchus mykiss) and lake trout (Salvelinus namaycush)
Full text linkThe objectives of this study were to investigate acoustic tag burden in two juvenile salmonid species; rainbow trout (Oncorhynchus mykiss) and lake trout (Salvelinus namaycush), explore the relationship between metabolic rate and swimming performance in tagged and untagged individuals, and investigate effects of surgery and tag implantation on survival and growth. Laboratory experiments measured tag burden effects in fish sizes (e.g., 9-39 g and 105-159 mm (fork length; LF)) typically stocked by Ontario Ministry of Natural Resources and Forestry (OMNRF) and other natural resource management agencies. The analysis revealed no significant effects of acoustic tagging on survival, growth, oxygen consumption (ṀO2) (proxy for metabolic rate), and swimming performance (Ucrit). Rainbow trout ṀO2 (mass-specific rate of oxygen consumption) increased with time since surgery, and acoustic-tagged rainbow trout had elevated ṀO2 compared to control fish, but the effect was not significant (p = 0.024). The acoustic-tagged lake trout ṀO2 were not significantly different from the controls or the other treatments (i.e., PIT, sham, and acoustic-tagged) (p = 0.011). Rainbow trout (i.e., acoustic-tagged and control fish) had a significantly higher Ucrit than lake trout (p < 0.001). Differences in swimming performance between the species was most likely influenced by water temperature and body size. For both species Ucrit was lower in acoustic-tagged fish but the difference was not statistically significant (p = 0.024). Rainbow trout were housed at ~ 14 °C and lake trout at ~ 11 °C. This study indicates that specific growth rate, oxygen consumption (via respirometry), and swimming performance (Ucrit) can be used as novel metrics to assess impacts of acoustic tag burden. The results from this acoustic tagging study suggest tag burden up to 6% does not have a significant effect on survival, growth, resting ṀO2, and swimming performance (Ucrit) in juvenile rainbow trout and lake trout
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