Eric G. Johnson

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.