Mark W. Fritts

Maternal meddling in neonatal sharks: implications for interpreting stable isotopes in young animals.

Stable isotopes of neonatal vertebrates reflect those of their mothers diet and foraging location. Evaluating feeding strategies and habitat use of neonates is consequently complicated by the maternal isotopic signal and its subsequent elimination with growth. Thus, methods that measure the loss of the maternal signal, i.e. when the isotopic signal of a neonate reflects its own diet, are needed. Values of δ(13)C and δ(15)N were measured in liver and muscle tissues of <1 year old bull (Carcharhinus leucas) and Atlantic sharpnose (Rhizoprionodon terraenovae) sharks and related to age using, total length, date sampled and umbilical scar stage (USS). We observed a decline in δ(13)C and δ(15)N values with age that was different among species, similar among isotopes, and greater in liver than in muscle; highlighting that retention of the maternal signal is dependent on species-specific life history and tissue characteristics. USS was most effective for assessing the loss of the maternal isotopic signal in the faster growing Atlantic sharpnose shark, but was less effective for the slower growing bull shark. Total length and date sampled were overall less effective and may be more informative for slower growing species when coupled with USS, as variable size at birth and misclassification of animals >1 year old, which remain in nursery habitats, increase the variability of the isotopic values. Consideration of the maternal signal and measuring its loss are thus necessary when analyzing the stable isotopes of young animals, as there is potential to misinterpret feeding strategies, over-estimate trophic position and incorrectly assign carbon source.

Variable δ15N Diet-Tissue Discrimination Factors among Sharks: Implications for Trophic Position, Diet and Food Web Models

The application of stable isotopes to characterize the complexities of a species foraging behavior and trophic relationships is dependent on assumptions of δ15N diet-tissue discrimination factors (∆15N). As ∆15N values have been experimentally shown to vary amongst consumers, tissues and diet composition, resolving appropriate species-specific ∆15N values can be complex. Given the logistical and ethical challenges of controlled feeding experiments for determining ∆15N values for large and/or endangered species, our objective was to conduct an assessment of a range of reported ∆15N values that can hypothetically serve as surrogates for describing the predator-prey relationships of four shark species that feed on prey from different trophic levels (i.e., different mean δ15N dietary values). Overall, the most suitable species-specific ∆15N values decreased with increasing dietary-δ15N values based on stable isotope Bayesian ellipse overlap estimates of shark and the principal prey functional groups contributing to the diet determined from stomach content analyses. Thus, a single ∆15N value was not supported for this speciose group of marine predatory fishes. For example, the ∆15N value of 3.7‰ provided the highest percent overlap between prey and predator isotope ellipses for the bonnethead shark (mean diet δ15N = 9‰) whereas a ∆15N value < 2.3‰ provided the highest percent overlap between prey and predator isotope ellipses for the white shark (mean diet δ15N = 15‰). These data corroborate the previously reported inverse ∆15N-dietary δ15N relationship when both isotope ellipses of principal prey functional groups and the broader identified diet of each species were considered supporting the adoption of different ∆15N values that reflect the predators’ δ15N-dietary value. These findings are critical for refining the application of stable isotope modeling approaches as inferences regarding a species’ ecological role in their community will be influenced with consequences for conservation and management actions.

Critical linkage of imperiled species: Gulf Sturgeon as host for Purple Bankclimber mussels

Abstract.  One of the largest impediments to the conservation of freshwater mussels is the absence of host-fish data. Suitable hosts must be present in sufficient numbers and occur at the appropriate time for successful mussel recruitment. Habitat degradation and fragmentation caused by dams and other anthropogenic alterations may reduce host availability. Host data are lacking for the federally threatened Purple Bankclimber mussel (Elliptoideus sloatianus), which is endemic to the Apalachicola–Chattahoochee–Flint basin (ACF) in Alabama, Florida, and Georgia, and the Ochlockonee basin in Florida and Georgia. We tested 29 fish species in 7 families as potential hosts for Purple Bankclimbers and observed high metamorphosis success (79–89%) with 4 species of sturgeon: Gulf (Acipenser oxyrinchus desotoi), Atlantic (Acipenser oxyrinchus oxyrinchus), Lake (Acipenser fulvescens), and Shortnose (Acipenser brevirostrum). Metamorphosis was less successful with Blackbanded Darters (Percina nigrofasciata) and Halloween Darters (Percina crypta) as hosts (34–36% metamorphosis), and the remainder of the fishes we tested were not suitable hosts. The federally threatened Gulf Sturgeon is the only sturgeon species present in the ACF, but access of this migratory fish to most of the basin is blocked by Jim Woodruff Dam on the Apalachicola River. In the absence of sturgeon upstream of Jim Woodruff Dam, darters appear to have facilitated persistence of this mussel species, but at abundances far lower than historical conditions. This relationship between the Purple Bankclimber and Gulf Sturgeon is the first description of a federally protected fish serving as a host for a federally protected mussel and is an archetypal example of the role of habitat fragmentation in the ecology of listed species. Recovery of the Purple Bankclimber and other mussel species probably will require restoration of habitat connectivity for fish passage.

Freshwater mussel shells (Unionidae) chronicle changes in a North American river over the past 1000 years

The Illinois River was substantially altered during the 20th century with the installation of navigational locks and dams, construction of extensive levee networks, and degradation of water quality. Freshwater mussels were affected by these changes. We used sclerochronology and stable isotopes to evaluate changes over time in age-and-growth and food sources for two mussel species: Amblema plicata and Quadrula quadrula. Specimens were collected in years 1894, 1897, 1909, 1912, 1966, and 2013, and archeological specimens were collected circa 850. The von Bertalanffy growth parameter (K) was similar between 850 and 1897, but it increased by 1912 and remained elevated through 2013. Predicted maximum size (Linf) increased over the past millennium, and 2013 individuals were over 50% larger than in 850. Growth indices showed similar patterns of continual increases in growth. Shells were enriched in 13C and 15N during the 20th century, but exhibited a partial return to historical conditions by 2013. These patterns are likely attributable to impoundment, nutrient pollution and eutrophication beginning in the early 20th century followed by recent water quality improvement.

Ecological Recovery of a River Fish Assemblage following the Implementation of the Clean Water Act

The twentieth century spanned an era that included nadirs in environmental quality and subsequent efforts to improve ecological conditions. The Illinois Waterway, a large river system in Illinois, experienced prolonged degradation followed by a dramatic recovery. In the 1950s, a standardized sampling program was initiated that has continued for six decades. The resulting record documents profound ecological changes, demonstrating the potential for river ecosystems to recover following the successful implementation of large-scale policies, notably the Clean Water Act. Over six decades, native species diversity has increased, and one of the most prolific invasive fish species has collapsed. In addition, the sampling record highlights the recovery of socioeconomically valuable sport-fish populations. We examined the causes and consequences of change in a large river using data from a long-term monitoring program with unique spatial and temporal extent. The trends documented in the Illinois Waterway are relevant for the restoration of river systems worldwide.

Status and Genetic Character of Atlantic Sturgeon in the Satilla River, Georgia

AbstractThe Atlantic Sturgeon Acipenser oxyrinchus oxyrinchus is an important component of biodiversity along the Atlantic coast of North America, but most populations have been decimated by habitat degradation and chronic overfishing. Historically, spawning populations existed in all major Atlantic coast rivers from the St. Lawrence River, Quebec, to the St. Johns River, Florida, but fisheries surveys conducted in the past two decades suggest that several populations at the southern extent of this range are now extirpated or have declined to remnant status. Our objective was to assess the abundance and genetic character of Atlantic Sturgeon in the Satilla River, Georgia. Using entanglement gears, we expended over 2,800 h of sampling effort and captured a total of 193 Atlantic Sturgeon in tidally influenced reaches of the river during 2008–2010. Of the 157 fish that were collected in 2010, 72 were identified as river-resident juveniles (ages 0–1). Genetic analyses of a subset (n = 61) of these juveniles r...

Survey of Intersex Occurrence in Largemouth Bass (Micropterus salmoides) from the Upper Illinois River Waterway

Abstract Intersex condition (ooctyes in testicular tissue) has been documented in many watersheds among a diverse variety of fishes worldwide. However, few studies have tested for the occurrence of the condition in fishes from rivers of the American Midwest. Midwestern watersheds, such as the Illinois River Waterway, U.S.A. may provide important new information about the effects of endocrine disrupting chemicals (EDCs) on fishes because of the variety of urban, industrial, and agricultural land uses within the watersheds. A first step in the study of EDCs in any ecosystem is a survey to document the symptoms of EDC exposure, such as intersex condition. Our objective was to test for intersex condition in male largemouth bass Micropterus salmoides in the lower Des Plaines River, an area directly affected by surface runoff and wastewater effluents from the Chicago Metropolitan Area. Histological analysis indicated that testicular oocytes were present in 21 of 51 (41%) largemouth bass sampled and oocyte numbers ranged from 1–25/thin section among intersex individuals. Our study details the severity of intersex in a population of largemouth bass near a major metropolitan area, which represents an important contribution to the understanding of fish reproductive ecology in ecosystems with a history of environmental disturbance and recovery such as the Illinois River Waterway.

Freshwater mussel shells (Unionidae) describe anthropogenic changes to trace element cycling within a North American river

Bivalve shells provide an unparalleled opportunity for understanding the history of bioavailable trace elements in aquatic systems. The present study analyzed the elements Al, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, U, V and Zn in freshwater mussel shells collected from a large floodplain river. Shells were collected fresh, sampled from a historic archive, and retrieved from pre-Columbian archeological sites. The elements As, Co, Cu and Ni varied with time over the course of the 20th century. When compared to the pre-Columbian shells, 20th century shell concentrations for these elements were either consistently higher (Co, Cu and Ni) or lower (As). The 20th century shells also had consistently lower concentrations of Mn and Zn when compared to the pre-Columbian period, however diagenesis is the most likely cause of this difference in Mn. The elements Cd and Fe had little spatial or temporal variation in this data set. Several elements (Al, Cr, Hg, Pb, Se, U, and V) were below method detection limits in most shells. This study demonstrated that mussel shells can be used as archives of environmental history in river systems.

Estimating the Effects of Environmental Variables and Gear Type on the Detection and Occupancy of Large-River Fishes in a Standardized Sampling Program Using Multiseason Bayesian Mixture Models

AbstractSampling in non-wadeable rivers presents methodological challenges for monitoring fish species. Changing environmental conditions may affect the ability to accurately capture species (i.e., detection) and consequently may lead to inappropriate inferences on occupancy rates. We used hierarchical Bayesian multiseason mixture models to estimate occupancy and detection of 41 of 52 fish species in the Kankakee River, Illinois, by using data from a standardized monitoring program. Fish were sampled with AC boat electrofishing and shoreline seining over 7 years. Some centrarchids (e.g., Smallmouth Bass Micropterus dolomieu) were efficiently sampled by boat electrofishing, whereas most other species had low detection probabilities. Moderate changes in environmental conditions, such as water velocity and temperature, produced moderate changes in detection and occupancy. Generally, when species had high detection probabilities, changes in environmental conditions produced relatively small changes in the est...

Freshwater mussel (Unionidae) shells document the decline of trace element pollution in the regional watersheds of Chicago (Illinois, USA)

The present study analyzed trace element concentrations from the shells of native freshwater mussels collected from the headwater tributaries of the Illinois River (USA). These analyses were conducted to determine whether (A) anthropogenic enrichment could be observed and (B) whether enrichment had decreased following the enactment of Clean Water Act legislation in the 1970s. Collections archived in museums allowed comparison of the pre-Columbian period, the mid-20th century, and the early 21st century. The element Cu was consistently elevated above pre-Columbian baselines, while the elements As, Cd, Fe, and Zn were elevated in some collections. Although higher than baseline, concentrations Zn consistently declined from the mid-20th century to modern times, although differences occurred at individual sites. There was evidence for food web influence: the element Mn was significantly negatively correlated to sediment primary productivity as indexed by shell δ13C and Cu was positively correlated to trophic position as reflected by shell δ15N. Zn correlated to stream order across all time periods. We conclude that a mixture of historic factors affecting pollution control and land use patterns in the watershed led to sometimes conflicting effects on trace element bioaccumulation in mussel shells.