Search

Some freshwater fishes occur regularly in estuarine areas that experience spatial and seasonal variation in marine influence. These dynamic abiotic and biotic conditions potentially influence food consumption and growth. We found that effects of an estuarine environment on the growth of largemouth bass ( Micropterus salmoides) in Alabama's Mobile-Tensaw River Delta depended on body size, distance from the marine source, and amount of freshwater inflow. Incremental growth analyses demonstrated that young largemouth bass (

Estuaries are productive, heterogeneous, and dynamic systems that support a diverse array of fishes. However, our understanding of how presumably stenohaline fishes persist in such transitional systems is limited, particularly for most fishes in tidal freshwater areas. We conducted a laboratory experiment and field investigation along an upstream–downstream salinity gradient in the Mobile–Tensaw River Delta, Alabama, USA, to test the hypothesis that age-0 largemouth bass (Micropterus salmoides), an economically and ecologically important freshwater species that uses low-salinity habitats in many North American estuaries, move to avoid seasonal salinity increases. To do so, we quantified changes in otolith microchemistry (e.g., Sr to Ca ratios) along the major growth axis of otoliths in both field-collected and laboratory-reared individuals. Our experiment revealed a 21-day lag time between initial salinity changes and Sr:Caotolith saturation but that Sr:Caotolith in field-collected fish reflect changes in ambient salinity. Further, contrary to our expectation, otolith microchemical analyses from spring- and fall-collected age-0 largemouth bass indicate no avoidance of increased salinity, which has potential implications for their growth and recruitment in these systems. [ABSTRACT FROM AUTHOR]

Most community-based models in ecology assume that all individuals within a species respond similarly to environmental conditions and thereby exert identical effects as consumers or prey. Rather, individuals differ among systems, with important implications for population demographics and community interactions. For widely distributed assemblages made up of poikilotherms with high first-year mortality, species-specific differences in growth reaction norms as affected by both temperature and genotype will influence biotic interactions. For a broadly distributed fish assemblage, first-year growth does not vary with latitude for planktivorous prey species, but declines with increasing latitude for a terminal piscivore. Size-based competitive interactions between these species are likely to be more intense at high latitudes, as they spend an extended time sharing resources during early life. Such patterns probably are pervasive and must be considered when seeking to understand species interactions. Improving our knowledge of how temperature and local adaptations affect size-based interactions should enhance our ability to manage and conserve widespread assemblages.

Focuses on a study which illustrates the success from the technique used to detect relationships in continuous bivariate data. Information on the technique used; Details on changes in variance of a dependent variable from test results; Indepth look at the traditional tools used to assess patterns in bivariate data.

Enhancements to acoustic telemetry technology now allow for tracking aquatic animal movements at multiple spatial and temporal scales. While large acoustic arrays allow for broad-scale tracking of movement and migrations at scales of thousands of km across multiple years, more focused smaller arrays offer the potential to quantify fine-scale movement across shorter time frames. Investigators seeking to quantify movement at multiple scales may require a double-tagging approach if their telemetry systems and tag capabilities are different (e.g., 69 kHz for broad-scale, and 307 kHz for sub-meter fine-scale). We tested multiple double-tagging approaches (InnovaSea-Vemco V9 and HTI-495LY tags) for American shad Alosa sapidissima during three individual tank survival experiments including: 1) two free-floating acoustic tags and a dart tag, 2) two acoustic tags attached to one another and a dart tag, and 3) two acoustic tags attached to one another with no dart tag and revised handling and tagging techniques to reduce stress. In each experiment, we used a mixed effects Cox's proportional hazard model to test for differences in relative survival between groups (double acoustic tagged and control fish). At the completion of each experiment, all fish were X-rayed to evaluate tag placement in the body cavity. During the first experiment, American shad that received two free-floating tags and a dart tag had significantly lower relative survival compared to control fish after three weeks. The second experiment with treatment fish receiving two attached tags and a dart tag still had lower survival compared to control fish, but the magnitude of survival differences between treatment and control was lower compared to experiment one. In the third experiment, when two attached tags were used, dart tags were eliminated, and changes to fish handling and tagging techniques were implemented (new tagging apparatus, addition of lubricant, and different fish orientation) survival was equal among treatment and control fish. X-ray images showed distinct differences in post-mortem tag positioning between the first experiment (misaligned tags) compared to the second and third experiments (tags horizontally aligned within intestinal tract). American shad are generally difficult to study experimentally and sensitive to collection, handling, and surgical implantation. Our study showed strong evidence that attaching two acoustic tags to one another to create a single, larger tag improved survival and reduced internal tag misalignment. Fine- and broad-scale acoustic telemetry studies can be achieved with aquatic animals, but care must be taken with all species, and particularly those susceptible to handing stress to minimize tagging effects (e.g., mortality, altered movement behaviors, and tag burden). • Quantifying fish movement across multiple spatial scales may require a double-tagging approach. • American shad tagged with two free-floating acoustic tags survived at lower rates than control fish. • Attaching two acoustic tags together resulted in equal survival of tagged and control fish. • Findings identified novel double-tagging methods that can be applied to acoustic telemetry studies in the field. [ABSTRACT FROM AUTHOR]

Gizzard shad (Dorosoma cepedianum) population characteristics vary with lake productivity, competing with and providing prey for sport fishes. Because age-0 gizzard shad (>30 mm total length) are facultative detritivores, they can link benthic energy, carbon, and nutrients to pelagic food webs. To determine how age-0 gizzard shad success varies along a detritus-quality gradient, we completed a 15-day laboratory experiment in which age-0 gizzard shad fed lake sediment and starved gizzard shad both suffered high mortality, whereas fish fed zooplankton grew and survived well. This suggested that detritus alone is insufficient to ensure gizzard shad growth and survival. When sediment quality was high in outdoor mesocosms, density-dependent factors led to rapid growth only at low fish density and high-quality sediments; however, survival generally increased with sediment quality, regardless of gizzard shad density. In four small reservoirs, annual growth of gizzard shad increased with sediment quality. Collectively, our findings suggest that detritus quality ultimately can contribute to regulation of community and ecosystem productivity, mediated by its influence on gizzard shad biomass available for trophic transfer to gape-limited predators (i.e., piscivorous fish). This role of gizzard shad can link higher trophic levels in aquatic food webs to allochthonous detritus subsidies from the surrounding watershed. [ABSTRACT FROM AUTHOR]