Thesis (M.S.)--Ohio University, June, 2006. / Title from PDF t.p. Includes bibliographical references (p. 66-73)

<p>The general diet of Sufflogobius bibarbatus in the northern Benguela upwelling ecosystem was investigated from gut content analysis in two separate studies. The first study was conducted over two 48 h diel sampling stations onboard the RV Dr. Fridtjof Nansen during a dedicated cruise conducted in January 2006, whilst the second was conducted on cruises of opportunity aboard the RV Welwitschia during 2001 and 2002. The results of both studies indicate that S. bibarbatus has a fairly generalised diet, feeding on benthic and pelagic animals for the most part: phytoplankton was uncommonly reported from the 3739 fish examined. Larger fish ate primarily benthic organisms, whereas smaller individuals include substantial number of pelagic organisms in their diet. There would appear to be a clear relationship between the environment occupied by individuals and their diet: large fish are predominantly demersal and display limited vertical migration, whilst small fish are thought to be more pelagic. Results strongly indicate that this species is opportunistic. The present study sheds new light on the ecology of the species, which is becoming increasingly important in the region.</p>

Thesis (M.S.)--University of North Texas, 2001. / Title from PDF title page (viewed on Dec. 9, 2004). Includes bibliographical references (p. 51-57).

Thesis (M.Sc.)--Memorial University of Newfoundland, 2002. / Restricted until October 2003. Bibliography: leaves 93-103.

published_or_final_version / Ecology and Biodiversity / Master / Master of Philosophy

This thesis examines broad-scale patterns in the food web structure of lake ecosystems. The unifying framework for this analysis is the concept of trophic position, which represents the energy-weighted trophic path length leading to a consumer or population. Trophic position was estimated for over 550 populations of fish (16 species) using quantitative dietary data. A method to estimate trophic position of aquatic consumers using stable isotope ratios was developed; this involved correcting for within and among-lake variation in delta15N of primary consumers (organisms used to represent the base of the food web). We report an overall correspondence between dietary and isotopic estimates of trophic position; for each species, trophic position generally ranged the equivalent of one trophic level unit among-populations. The concept of discrete trophic levels provided only a qualitative description of energy flow pathways in aquatic food webs. Among-population variation was much greater than within-population variation in trophic position of lake trout. Long-standing hypotheses about the determinants of food chain length were examined; food chain length was most closely correlated with species richness and lake area. / The trophic position approach was used to examine two separate environmental problems relevant to lakes: the bioaccumulation of persistent contaminants in food chains and the impacts of invasive species. Trophic position was the major determinant of PCB levels in lake trout; these relationships were used to characterize biomagnification factors (BMFs) for this and a number of other contaminants. Furthermore, the introduction of smelt into lakes was linked to increased levels of PCB and Hg contamination in lake trout. Stable isotopes were used to quantify the impacts of smallmouth bass and rock bass invasions on food webs leading to lake trout. Lake trout from invaded lakes exhibited reduced consumption on littoral prey fish; a food web shift that is likely to have detrimental impacts on native lake trout populations.

<p>The general diet of Sufflogobius bibarbatus in the northern Benguela upwelling ecosystem was investigated from gut content analysis in two separate studies. The first study was conducted over two 48 h diel sampling stations onboard the RV Dr. Fridtjof Nansen during a dedicated cruise conducted in January 2006, whilst the second was conducted on cruises of opportunity aboard the RV Welwitschia during 2001 and 2002. The results of both studies indicate that S. bibarbatus has a fairly generalised diet, feeding on benthic and pelagic animals for the most part: phytoplankton was uncommonly reported from the 3739 fish examined. Larger fish ate primarily benthic organisms, whereas smaller individuals include substantial number of pelagic organisms in their diet. There would appear to be a clear relationship between the environment occupied by individuals and their diet: large fish are predominantly demersal and display limited vertical migration, whilst small fish are thought to be more pelagic. Results strongly indicate that this species is opportunistic. The present study sheds new light on the ecology of the species, which is becoming increasingly important in the region.</p>

Nearshore larval fishes were collected with an oblique trawl tow during day and night from mid-May to August 2010 and 2011 in the Indiana waters of Lake Michigan to determine diel differences in the distribution, depth, and abundance of larval fishes. Alewife, spottail shiner, yellow perch and round goby were the prevailing larval species. Alewives dominated the catch and were in highest abundance near East Chicago. In general, night catch rates were greater when compared to day catch rates, suggesting a diurnal difference in trawl susceptibility. Stratified larval trawling was subsequently conducted during June and July 2011 to detect whether diurnal vertical migration existed, potentially affecting day and night catch rates. Vertical migration was not detected in the stratified larval sampling, eliminating it as a factor in higher nighttime catch rates. Further, the most common fish, alewife, was measured (TL) to determine whether size was a factor in trawl avoidance and to provide information regarding trawl selectivity. Night trawls yielded larger size classes of alewife, potentially explaining higher nighttime catch rates. These data suggests a size bias of our larval trawl exists when comparing day and night samples, as well as the limited efficiency of our trawl to catch larger larval size classes. / Department of Biology

To monitor and assess direct anthropogenic impacts on an aquatic system requires knowledge of its natural variation. The goal of this study explored natural variation in the lake fish communities of the northern Bruce Peninsula, which may act as a reference condition for other studies. The results of this study indicated there has been a shift towards more small-bodied, native species present in the fish communities, potentially a result of beaver activity in the area. A second goal was to calculate gear sampling efficiencies to enable the design of efficient monitoring protocols for fish communities in small, shallow lakes. It was concluded that a wide variety of gears are required to assess the fish species composition in a lake. Fine-mesh hoops were the most effective gear; however, saturation was never obtained for boat electrofishing; therefore, additional research is required to determine effectiveness relative to the fine-mesh hoop net.

To monitor and assess direct anthropogenic impacts on an aquatic system requires knowledge of its natural variation. The goal of this study explored natural variation in the lake fish communities of the northern Bruce Peninsula, which may act as a reference condition for other studies. The results of this study indicated there has been a shift towards more small-bodied, native species present in the fish communities, potentially a result of beaver activity in the area. A second goal was to calculate gear sampling efficiencies to enable the design of efficient monitoring protocols for fish communities in small, shallow lakes. It was concluded that a wide variety of gears are required to assess the fish species composition in a lake. Fine-mesh hoops were the most effective gear; however, saturation was never obtained for boat electrofishing; therefore, additional research is required to determine effectiveness relative to the fine-mesh hoop net.