D. Allen Rutherford

Diel and Seasonal Patterns of Spotted Gar Movement and Habitat Use in the Lower Atchafalaya River Basin, Louisiana

Abstract We used radiotelemetry to determine diel and seasonal movements, habitat use, and home range behavior of 37 adult spotted gars Lepisosteus oculatus in the Atchafalaya River basin, Louisiana. The Atchafalaya River exhibits a distinct spring flood pulse each year, inundating a 3,640-km2 floodplain that includes a complex network of canals, bayous, and lakes. During nonflood months, diel locations of 27 fish recorded at 2-h intervals (median = 24 locations/fish) indicated that most spotted gars were shoreline oriented (P < 0.0001), preferred submerged branches as cover, and avoided areas of exposed bank (P < 0.0001). Median spotted gar movement rates were higher during summer (40.4 m/h) than fall–winter (15.1 m/h), and during both seasons, rate of movement and percentage of home range used were significantly greater at night than during dawn, day, or dusk periods (P < 0.03). Increased nocturnal activity appeared to be related to feeding periodicity, as a substantially greater proportion (70%) of spo...

Growth, Fecundity, and Mortality of Paddlefish in Louisiana

Abstract Growth, mortality, fecundity, egg diameter, and age at maturity were determined from samples of 270 paddlefish Polyodon spathula collected from the Atchafalaya River basin and Lake Pontchartrain, Louisiana, during a commercial harvest moratorium from 1987 to 1989. Early growth of paddlefish determined from back-calculation of annular measurements on dentary cross sections was high relative to paddlefish populations in the upper Mississippi River drainage; lengths of age-1 fish ranged from 411 to 455 mm in eye-fork length. Natural mortality of Louisiana paddlefish was high (26–48%), and data suggested a reduction in age at maturity (100% females mature at age 10), lower fecundity (average fecundity, 9,500 eggs/kg body weight), and larger eggs (average diameter, 2.67 mm) relative to other paddlefish populations. Changes in reproductive life history characteristics may reflect rapid growth and high natural mortality rates. As the postmoratorium commercial fishery for Louisiana paddlefish develops, c...

Hydrology and aquatic habitat characteristics of a riverine swamp: II. Hydrology and the occurrence of chronic hypoxia

We examined the temporal and spatial occurrence of hypoxia (dissolved oxygen concentrations<2.0 mg L−1) in a 254-km2 portion of the Atchafalaya Basin floodway for 25 months (September 1993–September 1995) and analysed its relationship to local and basin-wide hydrology. Hypoxia occurred in channels with low turbulence whenever a flood pulse traveled through the system and mean water temperature exceeded 15°C. The number of hypoxic stations was linearly related to both river stage and air temperature. Tidal fluxes and weather-related variables (i.e. wind speed and direction, accumulated rainfall) did not significantly influence when, or the number of stations at which, hypoxia occurred. Additionally, hypoxia occurred at different times within different regions of the swamp. Total organic-carbon concentrations were relatively low throughout the study area when hypoxia occurred, and (although we acknowledge limitations of our data) we suspect that regional differences in organic-matter concentrations (leading to differences in metabolic consumption of dissolved oxygen) had little effect on when or where hypoxia occurred. Instead, we believe that regional paths of water flow affected how water was transported from turbulent-flowing channels into and through channels containing low- or non-turbulent flows. Water movement out of channels with low turbulence was impeded in each region during different stages of the flood pulse, and this event coincided with the most extensive occurrence of hypoxia within each region. The magnitude and duration of the flood pulse as well as the interior paths of water flow significantly influenced the severity and duration of hypoxia in this riverine swamp. Copyright

Influence of Physicochemical Characteristics on Annual Growth Increments of Four Fishes from the Lower Mississippi River

Abstract We examined relationships between lower Mississippi River physicochemistry and growth of young (≤age 2) blue catfish Ictalurus furcatus, channel catfish I. punctatus, freshwater drum Aplodinotus grunniens, and gizzard shad Dorosoma cepedianum collected from dike fields (river kilometers 669.0–883.2 upstream from the mouth) in September and October 1987–1990. Growth increments of the four fishes were determined from cross sections of otoliths (freshwater drum and gizzard shad) or spines (blue and channel catfishes), and we used regression analysis to assess the effects of annual variability in 15 physicochemical variables on growth. We hypothesized that growth of these fishes would be positively related to the extent and duration of the annual flood pulse, as it is in tropical floodplain systems. However, growth increments of age-0 blue catfish, channel catfish, and gizzard shad were related only to length of the growing season. Further, positive relationships between growth and total organic carb...

Hydrology and aquatic habitat characteristics of a riverine swamp: I. Influence of flow on water temperature and chemistry

We monitored water temperature, air temperature, hydrologic characteristics, and chemical variables for 25 months in a 254-km2 portion of the Atchafalaya Basin, Louisiana, USA, a distributary swamp of the Mississippi River. We related observed trends in thermal and chemical variables to characteristics of the flood pulse, available channel types, and paths of water flow within the study area. Dissolved oxygen (range 0.05–13.05 mg L−1), percent oxygen saturation (range 0.6–142.4%), and pH (range 6.31–8.52) increased as river stages decreased, and water temperatures (range 4.75–32.25°C), specific conductance (range 207.8–931.5 μmhos), and the top–bottom difference in dissolved oxygen (−7.5–12.05 mg L−1) increased as air temperatures rose. The maximum variance observed for all chemical and thermal habitat characteristics occurred during periods when air temperatures exceeded, and river stages were less than, their respective medians observed during the study. At any point in time, thermal and chemical variables varied most among stations in water courses with no visible water turbulence (low-energy channels), and these channels consistently had lower dissolved oxygen, percent oxygen saturation, and pH than turbulent water courses (high-energy channels) or lakes contained. Water was directed from the river into one region of the study area from two opposing directions, thereby impeding water flow through the region. Low-energy channels in this region consistently exhibited lower dissolved oxygen concentrations, percent oxygen saturation, and pH than was observed in low-energy channels of regions where water flow was unimpeded. The quantity and quality of aquatic habitat characteristics in riverine swamps can be manipulated by controlling the timing and magnitude of the flood pulse, relative availability of different water courses, and internal paths of water flow through the swamp. Copyright

Physicochemical Effects of the Flood Pulse on Fishes in the Atchafalaya River Basin, Louisiana

Abstract We examined the relationships between physicochemistry and the distribution and abundance of fishes at 36 sites in the lower Atchafalaya River basin (ARB), Louisiana, a bottomland hardwood swamp fed by waters (distributaries) of the Mississippi and Red rivers. We used principal components analysis (PCA) of the 29 most common ARB fishes to examine fish assemblage structure and then related the first two components to physical habitat (e.g., standing timber, submerged macrophytes, and brushy cover) and water quality (e.g., dissolved oxygen (DO), pH, and specific conductance) variables. To further examine the relationship between physicochemistry and species abundance and distribution, we regressed the habitat and water quality variables on the abundance of common ARB fishes. Regression analysis indicated that DO concentration, DO differential (surface less bottom), specific conductance, and current velocity were most strongly associated with fish distribution and abundance. A PCA of these four vari...

Characteristics of Woody Cover Used by Brown Madtoms and Pirate Perch in Coastal Plain Streams

Abstract We measured or described microhabitat characteristics of woody debris accumulations (i.e., structural complexity, cavity space, stein diameter, suspended and benthic leaves, depth, inside and outside flow, undercut bank, and lateral position) found in headwater coastal plain streams of central Louisiana. Debris characteristics at sites used as diurnal cover by adult brown madtoms Noturus phaeus and pirate perch Aphredoderus sayanus were compared with characteristics at unoccupied debris sites. Woody debris used by brown madtoms was characterized as having greater cavity space, structural complexity, and suspended leaves. Additionally, brown madtoms more frequently occupied debris areas located beneath undercut banks or next to areas of high flow. Of all the habitat variables, undercut bank and cavity space showed the strongest relationship with the presence of brown madtoms in woody debris. Brown madtoms demonstrated no significant difference in use of debris characteristics between small (34–83 ...

Patterns of Habitat Use among Vegetation-Dwelling Littoral Fishes in the Atchafalaya River Basin, Louisiana

Abstract Information regarding the relative value of different aquatic macrophytes as fish habitat is lacking for large floodplain river systems, such as the Atchafalaya River basin in south-central Louisiana. We made seasonal comparisons of fish (total length, <100 mm) density, diversity, and biomass and physicochemistry among submersed hydrilla Hydrilla verticillata, emergent bulltongue Sagittaria lancifolia, and floating water hyacinth Eichhornia crassipes. In addition, we examined the influence of habitat structure and physicochemistry on fish assemblage composition and density. Although there were no seasonal differences in fish biomass among plant types, hydrilla consistently supported the greatest fish density and diversity across seasons. While hydrilla and water hyacinth fish density changed little among seasons, density in bulltongue was higher during low water. Of the 12 most common fish species, the pirate perch Aphredoderus sayanus and yellow bullhead Ameiurus natalis showed no consistent pat...

Field and Laboratory Determinations of Hypoxic Effects on RNA-DNA Ratios of Bluegill

Abstract We used RNA-DNA ratios in both field and laboratory experiments to examine the effects of hypoxia on short-term growth of bluegill Lepomis macrochirus collected from the lower Atchafalaya River Basin, Louisiana. In the field experiment, RNA-DNA ratios of bluegill (17.8–52.3 g) from hypoxic habitats (DO < 2.0 mg L−1; n = 26) were significantly lower than ratios of bluegill from normoxic habitats (DO > 4.0 mg L−1; n = 31). In each of two laboratory experiments 40 bluegill (14.54–76.70 g) were individually placed in aquaria to test the effects of hypoxia on RNA-DNA ratios. Additionally, bluegill were fed at different rates in the first experiment to determine the effects of feeding level on RNA-DNA ratios. Results of the first experiment confirmed the sensitivity of RNA-DNA ratios to short-term changes in growth, as fed bluegill had significantly higher ratios than starved bluegill. In both experiments RNA-DNA ratios were not significantly different in bluegill subjected to hypoxia. Results of the study indicate that laboratory experiments did not adequately simulate increased bioenergetic demands and fluctuating DO levels found in hypoxic areas of the Basin.

Acidification of the Lower Mississippi River

Abstract Nonpoint-source pollutants are implicated in the global acidification of fresh waters. Our ability to differentiate the effects of point-source and nonpoint-source pollution on the acidification of large rivers is limited. Most studies of point-source discharges have been concerned with municipal programs for reducing biochemical oxygen demand, bacterial counts, and total phosphorus; few have addressed acidification of rivers. Because of the meager information on the role of nonpoint-source and industrial pollution in the acidification of large rivers, we examined long-term trends (and cyclic seasonal events) in pH, alkalinity, and selected ions in the lower Mississippi River basin from 1958 to 1986. Time-series analyses disclosed significant declines in pH and alkalinity and increases in strong acid anions in the lower 300 km (industrial corridor) of the lower Mississippi River. However, upstream from most industry on the Mississippi River and throughout the Atchafalaya River, where agricultural...