Wesley M. Daniel

Multifactorial model of habitat, host fish, and landscape effects on Louisiana freshwater mussels

Abstract. Unionoids are important in aquatic ecosystems, but despite their continued decline in diversity, few multifactorial studies have been done to identify determinants of their distribution and diversity. We studied the effects of multiple environmental factors on species richness and abundance at 65 sites in 6 major watersheds in the Pine Hills region, Louisiana. We surveyed in-stream habitat variables, land use/cover, and the co-occurring fish assemblages in 2nd- through 6th-order streams. A structural equation model suggested that 2 major latent variables were important: 1) reduced habitat disturbance, influenced by lower current velocity, substratum composed mostly of fine sediments, and increasing stream order, and 2) agricultural land use in riparian corridors and associated reduced water quality. These 2 latent variables explained 84% of mussel species richness and 48% of total mussel abundance. Mussel, but not host-fish species richness and abundance increased with stream order. Sites in the lower river basins had increased amounts of fine sediments and lower current velocities. We suggest that the lower river basins have extensive riparian wetlands that ameliorate the effects of frequent floods, thus mediating hydrologic disturbance and increasing mussel diversity.

AFS Position Paper and Policy on Mining and Fossil Fuel Extraction

Following a four-year period of writing, member comment, and multiple revisions, the AFS Position Paper and Policy on Mining and Fossil Fuel Extraction was approved unanimously by the membership at the Societys annual business meeting August 19, 2015, in Portland, Oregon. The entire document can be read at fisheries.org/policy_statements; a brief summary follows.

The role of life history and behavior in explaining unionid mussel distributions

In unionid mussels, it has been proposed that opportunistic life histories are adaptive in flashy tributaries, while equilibrium life histories and thicker, sculptured shells are adaptive in higher order streams. We sampled the distributions of 9 common mussels along a gradient in stream size in southeastern Louisiana, USA, to test for life history and behavior traits as explanations of longitudinal pattern of species distributions. We found two species distribution groups, cosmopolitan species, and higher order stream specialists. Shell sectioning revealed that cosmopolitan species matured earlier, had shorter life cycles, possessed lighter shells, and grew faster. We also studied mussel movement and sediment erosion around shells in the laboratory, and our results indicated that cosmopolitan species had faster rates of movement, and were better at tracking receding water levels in the laboratory, all traits that could be adaptive in flashier headwater streams, but also suffered more scouring in a laboratory flume than species with heavier shells and sculpture. Our results verify that mussel life histories and behavior help in understanding mussel distributions in rivers, and also suggest that higher order stream species may be more at risk to disturbances like spates.

Assessment of dam effects on streams and fish assemblages of the conterminous USA

Despite the prevalence of damming as a global disturbance to river habitats, detailed reach-based assessments of the ecological effects of dams are lacking, particularly across large spatial extents. Using data from nearly 50,000 large dams, we assessed stream network fragmentation and flow alteration by large dams for streams of the conterminous USA. We developed 21 dam metrics characterizing a diversity of dam influences operating at both localized (e.g., distances-to-dams) and landscape scales (e.g., cumulative reservoir storage throughout stream networks) for every stream reach in the study region. We further evaluated how dams have affected stream fish assemblages within large ecoregions using more than 37,000 stream fish samples. Streams have been severely fragmented by large dams, with the number of stream segments increasing by 801% compared to free-flowing streams in the absence of dams and a staggering 79% of stream length is disconnected from their outlet (i.e., oceans and Great Lakes). Flow alteration metrics demonstrate a landscape-scale disturbance of dams, resulting in total upstream reservoir storage volumes exceeding estimated annual discharge volumes of many of the nations largest rivers. Further, we show large-scale changes in fish assemblages with dams. Species adapted to lentic habitats increase with dams across the conterminous USA, while rheophils, lithophils, and intolerant fishes decrease with dams. Overall, fragmentation and flow alteration by dams have affected fish assemblages as much or more than other anthropogenic stressors, with dam effects generally increasing with stream size. Dam-induced stream fragmentation and flow alteration are critical natural resource issues. This study emphasizes the importance of considering dams as a landscape-scale disturbance to river habitats along with the need to assess differential effects that dams may have on river habitats and the fishes they support. Together, these insights are essential for more effective conservation of stream resources and biotic communities globally.

StreamThermal: A Software Package for Calculating Thermal Metrics from Stream Temperature Data

Improving quality and better availability of continuous stream temperature data allow natural resource managers, particularly in fisheries, to understand associations between different characteristics of stream thermal regimes and stream fishes. However, there is no convenient tool to efficiently characterize multiple metrics reflecting stream thermal regimes with the increasing amount of data from continuously recording data loggers. This article describes a software program packaged as a library in R to facilitate this process. With this freely available package, users will be able to quickly summarize metrics that describe five categories of stream thermal regimes: magnitude, variability, frequency, timing, and rate of change. The installation and usage instruction of this package, the definition of calculated thermal metrics, as well as the output format from the package are described, along with an application showing the utility for multiple metrics. We believe that this package can be widely utiliz...

The Population Ecology of the Threatened Inflated Heelsplitter, Potamilus inflatus, in the Amite River, Louisiana

Abstract We quantitatively sampled the threatened Inflated Heelsplitter (Potamilus inflatus) in the Amite River, Louisiana, U.S.A., and sectioned shells to study its life history, as well as electrofishing the river to determine the relative abundance of its host fish. Inflated Heelsplitters are currently limited to a 40 km stretch of the Amite River, east of Baton Rouge, although they are also found in two rivers in northwest Alabama. Densities averaged 0.1 m−2, with an aggregated dispersion pattern, making them the sixth most abundant species out of 15 species found in quantitative samples. Inflated Heelsplitters mature after 1 y, live for 8 y, and have a rapid growth rate (K  =  0.69/y). The average life span of eight other mussels in the Amite River is 24 y, and average age at maturity is 3.6 y. Sexual dimorphism may occur in Inflated Heelsplitters as it does in the related Bluefers (Potamilus purpuratus), with males reaching larger sizes. Inflated Heelsplitters have an opportunistic life history strategy (Haag, 2012), which may be well adapted to flashy rivers and low population densities. It is however a long term brooder, which has been linked to higher chances of extinction (Vaughn, 2012). The Freshwater Drum (Aplodinotus grunniens), the fish host of the Inflated Heelsplitter, was the 17th most abundant out of 44 fish species sampled in the Amite River. Its relatively rare host fish, anthropomorphic disturbances from upstream gravel mining, or increased urbanization of the watershed may be important in explaining the threatened status of the Inflated Heelsplitter.