Areas of Expertise
Population dynamics, Quantitative fisheries ecology and stock assessment, Ecosystem-based fisheries management, Reproductive Ecology, Stock enhancement of marine fisheries
B.A. (Biology and Economics) DePauw University (1994)
M.S. (Marine Biology) Florida Institute of Technology (1996)
Ph.D. (Marine Science) North Carolina State University (2004)
Postdoctoral Fellow (Estuarine Ecology) Smithsonian Environmental Research Center (2004-2006)
Joined UNF faculty in 2011
I am broadly interested in the integration of the principles of basic ecology and fisheries science to address important research questions related to commercial and recreational fisheries. This ecological approach to fisheries science provides a more holistic framework that explicitly recognizes the complex interconnections among species, their physical and living environments and human influences that combine to regulate fishery stocks. My work is interdisciplinary, integrating observational, experimental and quantitative modeling approaches, and the application of innovative research tools. Ultimately, my research goal is to advance our understanding of the population dynamics of fishery species and provide sound scientific information to managers and decision-makers as a basis for effective management, conservation and restoration of coastal living resources. I have a deep commitment to undergraduate and graduate student involvement in my research and seek to involve stakeholders and the general public directly in my research activities.
Population dynamics and connectivity. The dynamics of marine and estuarine species are often characterized by complex life histories involving long-distance dispersal among geographically separated local populations. Quantifying spatial variation in recruitment and nursery habitat value, and defining the ecologically relevant scales of connectivity among spatially distinct nurseries is essential to a full understanding of population dynamics, the management and conservation of fishery stocks, and to the design of marine protected areas. To address research questions in this area, I employ a variety of field sampling, tagging and modeling approaches. For example, an ongoing research focus has been estimating key demographic rates for juvenile blue crabs (e.g., growth, mortality, emigration) and how these rates vary both spatially and temporally to regulate local and regional population dynamics. This work is helping to support new fishery population and ecosystem-based management models, which now seek spatially explicit, life-stage dependent information, but which rely on an increasingly complex understanding of ecosystem processes.
Understanding patterns of fishery exploitation. I am investigating important questions related to fishery exploitation primarily using tag and release studies. Tagging studies can provide independent estimates of natural and fishing mortality, and can also provide valuable information about spatial and temporal distribution of the fishable stock. I have employed a large-scale tag and recapture programs to (1) estimate population size and survival rates (2) estimate fishery exploitation and the contribution of various fishery sectors (recreational vs. commercial) to the harvest, and (3) understand movement patterns and migratory behavior of fishery stocks. To conduct the extensive field tagging effort, we have engaged commercial watermen through a stakeholder participatory research program and enlisted the general public through citizen science initiatives. I am committed to transferring research findings to policy-makers to provide them with the best current science on which to base management decisions. Regulations based on sound science are not only most likely to be successful, but provide a clearly defensible and transparent rationale for managers when addressing the concerns of fishery stakeholders. My research findings are communicated to fishery managers and policy-makers through direct communications, workshops, and membership on local, regional and national advisory committees.
Hatchery-based restoration of marine fisheries. Researchers and management agencies are increasingly investigating the efficacy of alternative management strategies, including various forms of stock enhancement such as restocking, designed to aid traditional approaches to achieve stock recovery. Restocking involves the release of hatchery-reared animals into underutilized natural habitats to restore spawning stock abundance in an attempt to augment subsequent natural juvenile recruitment. Restocking may be particularly useful for severely depleted fisheries in which low levels of spawning stock and subsequent recruitment limitation hinder recovery. I have focused intensively on testing the potential of restocking as a tool for the restoration of depleted fishery stocks. Specific research foci have included the quantitative field assessment of restocking, estimation of demographic rates, comparison of wild and hatchery-reared animals, optimization of release strategies and protocols, examination of the potential impacts of, and ecological interactions between, hatchery animals and natural communities, and the integration of stock enhancement with traditional fishery management approaches.
Reproductive ecology. The overwhelming imperative in fisheries management is the prevention of recruitment overfishing, defined as depleting a stock to levels where future recruitment is significantly reduced. For crustacean fisheries, this has traditionally been accomplished through the protection of the female spawning stock; however this management paradigm ignores potential impacts of male demography on reproductive success. I am focusing intensively on two aspects of reproductive ecology using the blue crab as a model system, (1) understanding the impacts of fishery exploitation on the mature female blue crab spawning stock, and (2) investigating the potential for sperm limitation in blue crabs in Chesapeake Bay. The blue crab is an ideal species for this work because of their unique life history, intense male directed fishery and female centered conservation efforts. My research in this area begins with field studies at the level of the individual, and is then scaled to the population level using quantitative models.
Publications & Presentations
Ogburn, M.B., P.M. Roberts, K. Richie, E.G. Johnson, and A.H. Hines. 2014. Temporal and spatial variation in sperm stores in mature female crabs Callinectes sapidus and potential effects on brood production in Chesapeake Bay. Marine Ecology Progress Series 507:249-262.
Likely, R, E.G. Johnson, G.A. Ahearn. 2014. Functional characterization of a putative disaccharide membrane transporter in crustacean intestine. Journal of Comparative Physiology B. 185:173-183.
Gilg, M.R., E.G. Johnson, J. Gobin, B.M. Bright and A. Ortolaza. 2012. Population genetics of introduced and native populations of the green mussel, Perna viridis: determining patterns of introduction. Biological Invasions.
Long, W.C., E.F. Gamelin, E.G. Johnson and A.H. Hines. 2012. Density-dependent indirect effects: Apparent commensalism and apparent competition coexist in a two-prey system. Marine Ecology Progress Series 456:139-148.
Johnson, E.G., A.H Hines, A.C. Young, M.A. Kramer, M. Goodison, R. Aguilar, and M. Bademan. 2011. Field comparison of survival and growth of hatchery-reared versus wild blue crabs, Callinectes sapidus Rathbun. Journal of Experimental Marine Biology and Ecology 402:35-42.
Hines, A.H., E.G. Johnson, M.Z. Darnell, D. Rittschof, T.J. Miller, L.J. Bauer, P. Rodgers, and R. Aguilar. 2010. Predicting Effects of Climate Change on Blue Crabs in Chesapeake Bay. In: G.H. Kruse, G.L. Eckert, R.J. Foy, R.N. Lipcius, B. Sainte-Marie, D.L. Stram, and D. Woodby (eds.), Biology and Management of Exploited Crab Populations under Climate Change. Alaska Sea Grant, University of Alaska Fairbanks. doi:10.4027/bmecpcc.2010.22
Johnson, E.G., and D.B. Eggleston. 2010. Population density, survival and movement of blue crabs in estuarine salt marsh nurseries. Marine Ecology Progress Series 407:135-147.
Johnson, E.G., A.H. Hines, M.A. Kramer, and A.C. Young. 2008. Importance of season and size of release to stocking success for the blue crab in Chesapeake Bay. Reviews in Fisheries Science 16(2):254-261.
Aguilar, R., E.G. Johnson, A.H. Hines, M.A. Kramer, and M.R. Goodison. 2008. Importance of blue crab life history for stock enhancement and spatial management of the fishery in Chesapeake Bay. Reviews in Fisheries Science 16:117-124.
Eggleston, D.B., E.G. Johnson, G.T. Kellison, G.R. Plaia, and C. Huggett. 2008. Pilot evaluation of early juvenile blue crab stock enhancement using a replicated BACI design. Reviews in Fisheries Science 16(1):91-100.
Hines, A.H., E.G. Johnson, A.C. Young, R. Aguilar, M.A. Kramer, M. Goodison, O. Zmora, and Y. Zohar. 2008. Release strategies for estuarine species with complex migratory life cycles: Stock enhancement of Chesapeake blue crabs, Callinectes sapidus. Reviews in Fisheries Science 16(1):175-185.
Young, A., E.G. Johnson, J.L.D. Davis, A.H. Hines, O. Zmora, and Y. Zohar. 2008. Do hatchery-reared crabs differ from wild crabs, and does it matter? Reviews in Fisheries Science 16(2):262-268.
Eggleston, D.B., D, Parsons, G.T. Kellison, G. Plaia, and E.G. Johnson. 2008. Functional response of sport divers to lobsters with application to fisheries management. Ecological Applications 18(1):258-272.
Zohar, Y., A.H. Hines, O. Zmora, E.G. Johnson, R.N. Lipcius, R.D. Seitz, D.B. Eggleston, A.R. Place, E. Schott, and J.S. Chung. 2008. The Chesapeake Bay blue crab (Callinectes sapidus): A multidisciplinary approach to responsible stock enhancement. Reviews in Fisheries Science 16(1):24-34.
Eggleston, D.B., C.P. Dahlgren, and E.G. Johnson. 2004. Fish Density, diversity, and size-structure within multiple back reef habitats of Key West National Wildlife Refuge. Bulletin of Marine Science 75(2):175-204.
Eggleston, D.B., E.G. Johnson, G.T. Kellison, and D.A. Nadeau. 2003. Intense removal and non-saturating functional responses by recreational divers on spiny lobster prey. Marine Ecology Progress Series. 250:263-278.