Current Projects
Endocrine Disrupting Compounds (EDCs) and Intersex
Fish in NC Waterways


This project, funded by the North Carolina Wildlife Resources Commission, is aimed at understanding the effects of municipal, agricultural, and industrial sources of EDCs in state waterways and the effects that they have on fish.  In particular, we are interested in the incidence of the intersex condition in male fish (male fish that have oocytes in their testes).  Sample sites across the state have been determined based on GIS analysis and preliminary sampling to address seasonal aspects of EDC levels in water, sediment and fish tissue is underway.  Our fish analyses are focusing on black basses, lepomids (e.g., bluegill and redbreast sunfish), and catfishes, all of which are subjected to histological and pathological analyses.  The estrogenic potency of water and sediment at study sites is also being assessed.  These field data will be combined with laboratory studies to assess the potential for estrogen exposure to cause intersex and reproductive disruption in native fish populations.



Movement, Mortality and Distribution of Striped Bass in the Lower Neuse

Striped bass (morone saxatilis) is an economically and ecologically important anadromous fish native to the Atlantic coast of North America, including North Carolina.  It has experienced major declines from historic levels, but much effort has been made to rebuild their populations.  Many populations have recovered, however, the Neuse River population has shown no substantive increase in abundance, despite NCWRC stocking over 100,000 annually. 
The goals for my project are to use telemetry methods to: 1) estimate movement and mortality rates of the phase-II striped bass that are stocked in the lower Neuse River annually and relate this to seasonal and episodic changes in water quality 2) estimate movement, distribution and mortality rates (natural, fishing and hook and release) of sub-adult striped bass in the lower Neuse River and to also relate this to episodic changes in water quality.  



Influence of tilapia on sport fishes in North Carolina

Redbelly tilapia (Tilapia zilli) and blue tilapia (Oreochromus aureaus) are indigenous to Africa and the Middle East, but now occur all over the southern United States, including North Carolina.  Tolerance of variable salinity levels, oxygen availability, temperature, overcrowding and the ability to change to different trophic levels are all documented life history traits attributed to the high success upon introduction.  With the current dearth of knowledge about the influence of tilapia on the native fish, and hence the lack of regulations or required permits, managers are unable to prevent further introductions by private landowners.

The goals for this project are to: (1) quantify growth and maturity patterns of tilapia in Lakes Hyco and Julian, (2) examine trophic interactions among tilapia and sport fishes through quantification of diet and stable isotope data, (3) measure seasonal spatial-distribution patterns and use of thermal refugia for tilapia and sport fishes, and (4) develop laboratory-based studies to examine population genetics and/or thermal tolerance of tilapia from Lakes Hyco and Julian as well as from commercial fish hatcheries marketing these to private pond owners. 




Completed Projects

Mortality, Movement and Habitat Selection of Stocked Juvenile Muskellunge in North Carolina Rivers

Muskellunge (Esox masquinongy), a native species to western North Carolina rivers, have been stocked by the North Carolina Wildlife Resources Commission for over 30 years. However, there has been little research on muskellunge in southeastern United States and the status of the fishery in North Carolina is unclear. In this project, we studied stocked juvenile muskellunge on the New River. Specifically, we quantified the dispersal, mortality and habitat selection of stocked age-0 muskellunge. We used whip-antenna radio transmitter tags to actively track the muskellunge. Preliminary information was also collected on presumed existing adult spawning populations in other western North Carolina river systems. Our goal was to provide fisheries biologists with information to improve the management of southern muskellunge populations.



White bass movements and interactions with invasive white perch

In this project we studied seasonal movement patterns and habitat use of white bass (Morone chrysops), a popular reservoir sportfish. In particular, concern about declining populations, perhaps attributable to interactions with invasive white perch (Morone americana), has led to interest in how white bass use reservoir habitat during outside the spawning period. To address these questions we used acoustic telemetry and an array of passive receivers to track large scale, seasonal movement patterns. We also usde periods of active tracking to individually locate fish each month to better understand habitat use. In addition, data from active and passive tracking was used to estimate seasonal and yearly natural and fishing mortality of white bass. Finally, we  investigated the possibility of invasive white perch comping for resources with white bass. For this aspect of the project we depended on diet analysis, stable isotopes, and acoustic tracking of white perch. Our goal was to provide managers with important population characteristics needed to better manage white bass in southeastern reservoirs.



Coastal largemouth bass responses to hypoxia and tournament displacement

In this project, we were interested in understanding the effects of hypoxia and angling tournament displacement on the ecology and physiology of coastal largemouth bass.  In particular, we were interested in how episodic hypoxia and anoxia caused by storm events (e.g., hurricanes and tropical storms) influence habitat use, movement patterns, growth, and survival of resident bass.  We used passive and active acoustic telemetry to track the movements of tagged bass throughout the study area, and monitored water quality using remotely deployed data sondes in addition to active surveys. Additionally, we investigated the relationship between stress indicators (e.g., cortisol) and the ability of fish displaced during tournaments to disperse after release. These data were used to determine the effects of water quality variations and tournament displacement on movement and survival of the tagged fish.  Our goal was to provide information that can be used to improve management of the coastal largemouth bass population.



Large Reservoir Foodweb Dynamics

In this project we were generally interested in understanding how food web interactions and dynamics can better inform the management of individual species. Lake Norman is a 32,000+acre reservoir north of Charlotte, NC that has experienced a number of recent fish introductions. The impact of these introductions on sportfish recruitment and dynamics is not well understood. Through this joint NC State, NC Wildlife Resources Commission, and Duke Energy research project, we considered interactions among native and invasive species, and used an ecosystem model (Ecopath with Ecosym) to assess the individual and synergistic effects of invaders.  We also examined the fate of newly stocked striped bass, and quantified predation and competitive interactions over the first several days after stocking. 



Estuary Hypoxia

In North Carolina and elsewhere, there is concern that hypoxia (low DO) due to excessive nutrient loading is adversely affecting coastal ecosystems, but quantifying the effects on fish and other living resources remains difficult. Our prior work indicated that indirect effects (e.g., density-dependent reductions in growth and survival as fish crowd into oxygenated refuges) were potentially more important than direct effects, because most fish can detect and avoid DO levels that cause mortality or reduced growth. Therefore, if we are to understand the effects of hypoxia on estuarine fishes we have to evaluate the processes occurring in oxygenated refuges that potentially impact growth and mortality. Using juvenile spot, Leiostomus xanthurus, a representative estuary-dependent species, we determined the sensitivity and response time of two biological indicators of recent growth (RNA-DNA ratios in muscle tissue, and plasma levels of insulin-like growth factor I) to changes in environmental conditions, and applyed them in the field to assess the effects of hypoxia dynamics on growth. In so doing, we linked changes in water quality with impacts on fish growth and production in nursery habitats by quantifying the sublethal effects of hypoxia on juvenile estuary-dependent species. 



Mercury dynamics in aquatic systems and fish 

Mercury contamination of aquatic foodwebs and fish tissue is a global concern. Currently, a number of consumption advisories have been issued for common, widely consumed fish species. Because fish are the primary vector for moving mercury from aquatic systems to people, the need to understand factors that facilitate mercury bioaccumulation and contamination risk is substantial. Our collaborative group is taking a comprehensive approach to understanding species in systems throughout the state of North Carolina in an effort to better predict risk of mercury consumption. To date, we've completed research on the range of biotic and abiotic factors that drive mercury conversion (from elemental mercury to methylmercury, the toxic form) and bioaccumulation, and we've modeled factors that most influence human consumption risk. We've also quantified the influence of point-source mercury pollution (coal fired power plants) and examined the influence of local contaminant sources on fish tissue mercury. To better link natural resource management and human health concerns, we've analyzed the influence of fish body size on tissue mercury dynamics, and we've compared common fishery length regulations to EPA consumption guidelines based on size. Finally, using cutting-edge statistical and analytical approaches, we are working to produce a Bayesian Entropy model that will allow public health officials to predict mercury in fish tissue by tracking its movement from deposition to accumulation. 



Mercury content in commonly consumed NC seafood

We worked with charter boat captains and seafood markets to help local consumers make informed decisions by providing more accurate information about mercury contamination in six economically important species that are commonly caught and consumed in North Carolina.  Tissue samples for analysis of mercury content were taken from the following species when in season: mahi mahi, king mackerel, wahoo, porgy, red grouper, and triggerfish. Our local data were compared to EPA, FDA, and Seafood Watch List consumption recommendations. The purpose of our work was to support informed decisions about local, sustainable fish consumption by providing mercury information for commonly caught and consumed species in North Carolina.



White Perch Reservoir Dynamics

White perch invasion of inland lakes and reservoirs is becoming increasingly common across North Carolina and the continental U.S.  This project focused on two aspects of these invasions.  First, we evaluated patterns in life history and trophic dynamics of white perch in large reservoirs, and determined how these differences were driven by factors such as time since invasion and fish community dynamics.  We were also interested in the possible competitive interactions between white perch and two popular North Carolina sportfish, white bass and black crappie, and work with these species continues.  In municipal reservoirs (typically small impoundments), small white perch have become a dominant portion of the fish community while maintaining low densities and large sizes in other reservoirs.  A second research objective was to examine differences in white perch abundance and life histories in smaller systems and determine the trophic position of white perch across varying population structures.  Ultimately, we hope to combine information from both large and small reservoirs to gain a better understanding of the effects of white perch on invaded systems.



Carolina Madtom Ecology and Life History

In this investigation we were interested in learning more about the life history of an understudied, endemic madtom. This species now exists in only two river drainages in North Carolina, the Tar and the Neuse. Although little is known about the Carolina madtom, evidence exists that the species is in decline, and it is currently listed as Threatened in North Carolina. We examined habitat use of this madtom in both river drainages in an effort to determine why it seems to be doing relatively well in the Tar River drainage but continues to decline in the Neuse River drainage. Working in conjunction with the North Carolina Wildlife Resources Commission and with funding from a State Wildlife Grant, we addressed issues of distribution, abundance and habitat requirements of the Carolina madtom. We also completed field and laboratory trials of an artificial habitat that we developed, which has the potential for conservation and restoration use in impacted areas.