Overview:

We study fish throughout their ontogeny, with an emphasis on the population dynamics of the juvenile life stages. Many aspects of the juvenile life history remain poorly understood for marine fishes and our lab has worked to identify processes occurring during the first year of life that impact growth, survival, and eventual recruitment to adult stages. We use a broad range of methods in our research, including stable isotope analysis, histology, otolith chemistry and microstructure, acoustic and satellite tagging, mark-recapture, controlled laboratory experiments, and field surveys. Recent projects have been focused on the trophic dynamics of large pelagic fishes in the US South Atlantic, recruitment processes of juvenile red drum, the population ecology of southern flounder, and the demography and trophic ecology of invasive catfish in coastal river systems. Our work has routinely contributed science that is applied in the management and conservation of marine and estuarine fishes, mainly through cooperative partnerships with state and federal fisheries biologists that provide great opportunities for graduate training in the principles and practice of fisheries science.

Southern Flounder Population Ecology

Our lab has conducted research on several aspects of southern flounder population ecology in recent years. These efforts have produced new information on stock structure along the US South Atlantic coast, migratory timing, pathways, and distances, and explicit estimates of natural and fishing mortality, and emigration. Combined evidence from tag-returns, otolith morphology, population genetics, and otolith chemistry has indicated extensive mixing among southern flounder in the US South Atlantic basin, with the greatest contribution to connectivity being the pre- and post-spawning movements of adults. Within estuarine systems, southern flounder demonstrate resident behavior, remaining in specific locations (mean home range = 1-2 km) for months/years before spawning-related emigration. The timing of emigration appears highly predictable, with ~85% of individuals departing within a 30 day window over several consecutive years of observations. Loss rates from fishing and natural sources of mortality during estuarine residency can be high and variable. In North Carolina systems, fishery dynamics are complex with variation in harvest among sectors that also vary in space and time. Our current research has been focused on growth and mortality during the first year of life and the contribution of settlement habitat to these processes. We are also just beginning a large effort to use satellite tags to identify several features of adult behavior, including spawning aggregation areas and post-spawning movements that will aid our understanding of stock structure and future conservation efforts.

Impacts of Non-Native Catfishes

Blue and flathead catfish represent non-native species that have been introduced into several Atlantic coast rivers since the 1960’s. Both specie grow to large sizes (70-100+ lbs) and either consume a primarily fish diet (flathead catfish) or include fish in their diet at larger body sizes (blue catfish). Trophic studies in other regions (Georgia, Virginia) have revealed their potential to have considerable impacts on native fish communities, and previous work in North Carolina has documented well established populations of each species, as well as diverse diets that include several species of native fish fauna. In 2017, we began a project in the lower Cape Fear River ecosystem to examine their potential impacts to native fish communities. So far, we have documented broad age and size structure (20+ years old and sizes > 1m for flathead catfish), widespread distribution throughout three major tributaries of the ecosystem, high trophic positions, and resiliency to environmental disturbance. We are continuing this work to improve identification of digested fish prey using DNA barcoding, estimation of the size and age dependence of maturity and fecundity using histology, and tracking the seasonal movements of acoustically tagged individuals.

Juvenile Recruitment & Year Class Strength in Red Drum

As the state fish of North Carolina, red drum represent a valuable cultural and economic resource in the region. Located near the northern edge of their distribution along the Atlantic coast, North Carolina estuaries provide a unique opportunity to study several aspects of red drum ecology that may differ from patterns observed near the center of their range. These include migratory dynamics, adult spawning and growth dynamics, and importantly, juvenile recruitment. Our lab has focused research on several themes to identify patterns and processes contributing to juvenile red drum recruitment success. Specifically, we have studied arrival timing, habitat use, and cohort demographics in different estuaries, as well as the effects of settlement habitat on growth dynamics. We have studied the importance of winter severity to modify annual cohort strength and found that both the timing and frequency of passing cold fronts matters as much as the magnitude of temperature decline. Most recently, we have been focused on the oceanographic conditions that contribute most to the production of strong year classes, attempting to identify patterns of wind speed and direction, water temperature, and coastal productivity that align to promote cohort success. We have also been studying patterns of catch in a long-term juvenile abundance survey to determine how sampling design may introduce bias into the time series and the possible advantages of transitioning to a partial replacement survey platform.

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Overview:

Southern Flounder Population Ecology

Impacts of Non-Native Catfishes

Juvenile Recruitment & Year Class Strength in Red Drum

The Scharf Lab