MPE 2013+ Workshop on Chesapeake Fisheries: From Oysters to Economics

August 28 - 30, 2017
Morgan State University, PEARL Lab, MD

Midge Cozzens, DIMACS, Rutgers University, midgec at
Scott Knoche, Morgan State University, scott.knoche at
Richard Lacouture, Morgan State University, Richard.Lacouture at
Asamoah Nkwanta, Morgan State University, Asamoah.Nkwanta at
Fred Roberts, DIMACS, Rutgers University, froberts at
Abdul-Aziz Yakubu, Howard University, ayakubu at
Presented under the auspices of the DIMACS Special Program: Mathematics of Planet Earth 2013+.


Keith R. Criddle, Juneau Center for Fisheries and Ocean Sciences, University of Alaska Fairbanks

Title: Alternative Visions for Fisheries Governancethe Rights of Individuals versus the Interests of their Communities

At the heart of debates over the consequences of alternative governance structures in fisheries is the ageless philosophical dispute regarding the supremacy of the rights of individuals or of their community: are fishermen endowed with an unalienable right to fish and to dispose of their catches or are those rights circumscribed by the rights of fishery-dependent communities or other social constructs? This dispute has been sharpened by the emergence of governance regimes that limit entry and even more so by the emergence of governance regimes that create individual or collective rights to options to harvest dedicated shares of a fish stock. This paper reviews the legal basis of fisheries management in the US EEZ. That review is used to provide context for an examination of how the choice of governance structures affects the preeminence of individual liberty or social contracts and in turn affects the magnitude and distribution of benefits. The rancor of disputes over the evolution of governance regimes is found to be correlated with the magnitude of windfall benefits attributable to the change.

Katherine A. Daniell, The Australian National University

Title: Methods for Coordinating Stakeholder Engagement in Estuary Management: Reflections and Lessons from Australia and France

Estuaries are cradles of life for the communities who live around and within them. They are valued in multiple ways for the services they provide, including but not only food production, recreation, ecosystem services, navigation and amenity. Different groups of stakeholders such as oyster farmers, fishermen, housing developers, tourism operators, nearby on-land farmers, First peoples, residents, shipping or transport companies, environmental NGOs and different government agencies and groups, all put different weights of importance on these different values and what it means to effectively manage an estuary for them. This typically creates issues of conflict over how estuaries should be managed and the need to develop methods of decision-support and governance arrangements to support these multiple parties to find a commonly supported way forward. This presentation will explore such issues and some of the lessons learnt from action in and observation of estuaries in Australia and France, including the development of the Lower Hawkesbury Estuary Management Plan to Sydney's North. It will particularly examine the different methods, including more or less participatory modelling, that were used to attempt to support integrated decision-making for estuarine management, and present some reflections on their efficacy and what lessons might be of interest to other estuaries. Such lessons include the importance of developing organization teams for stakeholder engagement that include not only participatory methods specialists, but also key implementation champions who will be able to put the decisions and plans proposed by stakeholders into action. Any scientific models of estuarine processes developed also need to be resourced for the long-term and developed to specifically fit management decision needs to avoid them never being used in management practice.

Tom Ihde & Scott Knoche, Morgan State University, PEARL

Title: Improving Metrics for Decision-Making for Today's Fisheries: Impacts of Oyster Reef Restoration, Choptank River Complex, Maryland

Fisheries management is changing. Traditional fisheries management focuses on maximizing yield of a species often without consideration of many of the environmental drivers in which a species is living, growing, and reproducing. If a managed species is thought to be strongly linked to a prey species, assessments might also include prey trends. Most recently, there have been pioneering efforts to include temperature considerations directly into stock assessments, but this is not yet common practice. There has been growing recognition that environmental variability (e.g., trophic pressures, climate forcing, nutrient enrichment of system, et al.) can be important to explain and predict variability in population estimates and forecasts, and that these factors can often produce non-intuitive and non-linear changes when acting together. The incorporation of such drivers into fisheries management decision-making is commonly called Ecosystem Based Fisheries Management (EBFM). There are now well-established modeling approaches that forecast population trends in the context of multiple, non-additive factors influencing exploited populations. These efforts to date, however, have had limited success in enhancing management decisions in an ecosystem framework. If we are to move EBFM policy forward, decision-makers appear to need more useful metrics than what these models typically offer (i.e., biomass). We will describe the design of a project that links typical outputs of a fishery ecosystem model (Ecopath with Ecosim) to those of an economic impact approach (IMPLAN) to develop metrics in terms of jobs and revenue effects. The focus of our work is on an oyster reef restoration effort in a tributary of the Chesapeake Bay.

Olaf Jensen, Rutgers University

Title:An Introduction to Fishery Stock Assessment

Stock assessments are the mathematical models used to predict the impact of a hypothetical level of fishing on the future abundance of a harvested fish or invertebrate population (the stock). They are one of the primary scientific tools used by fishery managers when setting rules designed to achieve a desirable balance between harvesting now and leaving sufficient numbers of adults to ensure that the population is abundant in the future. At their most basic, they consist of a population model that tracks total biomass and accounts for removals from the population through harvest. More advanced models track the numbers and biomass of individuals within different age classes. The choice of model typically depends on the type of data available. Stock assessments include both a process model that tracks changes in the population size and an observation model that relates the available data to these changes in population size. In this presentation, we will review a variety of stock assessment models, discuss fitting of models to data, and identify key uncertainties in the use of stock assessment to guide management.

Scott Knoche, Morgan State University, PEARL

Title: Using a Discrete Choice Model to Examine Oyster Harvester Participation and Site Choice

On each legal harvesting day during the Maryland oyster harvesting season, oyster harvesters face two key decisions. First, there is the decision whether to take an oyster harvesting trip. Second, contingent on making the decision to take a trip, a harvester chooses which location (i.e., oyster bar) to visit. These harvester participation and site choice decisions can be modeled within a random utility discrete choice models framework, which posits that the utility associated with an alternative is a function of the characteristics of the alternative. Such a model can provide important insights into the tradeoffs made by harvesters (e.g., willingness to travel further to increase expected harvest) and can help managers understand how both the location and frequency of trips changes in the presence of site quality changes (e.g., change in expected harvest) and site quantity changes (e.g., the opening and/or closing of specific harvesting areas). To this end, I use Maryland Department of Natural Resources logbook data to model daily participation and site choice decisions made by oyster dredgers throughout the 2013-2014 oyster dredge season as a function of key categorical weather variables (below freezing air temperature, small craft warning wind speed) and site-specific variables (distance from port, mean daily historical harvest, and bar size). Variables signs are as expected abnormally cold and windy weather reduces the likelihood of taking an oyster harvesting trip. Site choice probabilities are negatively related to travel distance and positively related to expected harvest. Using model results, I provide a few basic scenarios to explore the effects of site quality and quantity changes on harvester decisions. Finally, I discuss current model limitations and plans for future research.

Collaborator who worked on various aspects of this work: Lisa Wainger

Doug Lipton, NOAA Fisheries

Title: Bringing Economics to Oysters in the Chesapeake Bay

In the post-World War II era, Chesapeake Bay oyster fisheries have undergone major shifts in resource condition, environmental factors and management. We review these changes in light of the impact that economics of the fishery had had on outcomes. In particular, we examine the economics of the repletion programs, the economics of planned introduction of alternative species, and the economics of the private aquaculture sector. Finally, after years of resource decline and management failures, it appears the current system of private aquaculture and innovative approaches to public fisheries is leading to a growing industry with significant potential to maintain fishing communities and contribute to the local economy.

Thomas Miller, University of Maryland

Title: Chesapeake Bay Blue Crab: Stock Assessment and Environmental Change

Management of blue crab in Chesapeake Bay has been based on advice from formal stock assessments since 1997. In the intervening decade these assessments have become increasingly sophisticated, currently incorporating both sex and stage structure into the model. However, these assessments have yet to evaluate the potential of environmental change to affect management advice. Here we present results of temperature effects on overwintering behavior, coastwide synchronization of population dynamics suggesting a role of climate forcing and the impacts of ocean acidification on growth. Together these three factors have the potential to dramatically alter the structure and results of future assessment models and management approaches. Population projection modeling suggests lack of overwintering will increase both r and limit reference points, whereas acidification will counteract these effects. Understanding the pattern and magnitude of environmental impacts on blue crab will be critical to ensure sustainable fisheries in the future.

Collaborators who worked on various aspects of this work: M. J. Wilberg, H. L. Glandon, A. R. Colton, and L. J. Bauer

Emily Moberg, Rutgers University

Title: Optimal harvest in a deteriorating environment

Deteriorating environmental conditions (e.g., due to climate change) negatively impact the vital rates of marine species, with implications for fisheries management. While the rent maximizing harvesting strategy in a constant environment has been well characterized, optimal management under changing conditions is less understood. We develop a bioeconomic model for a fi shery with compensatory growth and decreasing marginal harvest cost in a deteriorating environment. With it we show that (1) optimal escapement is largely independent of the stock size; (2) the stock is ` fished down' to a rent-dissipating level at a characteristic time after which fishing ceases; and (3) non-monotonic escapement policies are often optimal. Using the Beverton-Holt stock-recruitment model with Schaeffer harvest costs, we show that non-monotonic escapement can be optimal when fecundity decreases in time. Analysis of a simpler piecewise-linear model shows that non-monotonicity generally arises from an interaction between the deteriorating vital rate and density-dependent mechanisms of population regulation.

Elizabeth North, University of Maryland Center for Environmental Science

Title: OysterFutures: Applying a spatially-explicit model and testing a collaborative process for developing oyster fishing regulations in Chesapeake Bay

From forestry on mountains to fisheries in the ocean, people differ in opinion about how to use a natural resource. The processes used for developing regulations may lack science-based decision making and can result in clashes among stakeholders. For some fisheries, like that of the eastern oyster Crasosstrea virginica in Chesapeake Bay, the conflicts among stakeholder groups have existed for decades and the century-long decline in oyster populations has not been substantially reversed. The objective of the OysterFutures research program is to test a consensus-based process for developing fishing regulations and restoration policies that meets the needs of major stakeholders and integrates the latest scientific understanding of oysters, the fishing industry, and oyster ecosystem services in the Choptank and Little Choptank Rivers, tributaries of Chesapeake Bay. Through a series of facilitated meetings, stakeholders are participating in a science-based collaborative modeling process which allows them to participate in building the OysterFutures model which projects how well policies are expected to meet their objectives. This approach integrates spatially-explicit models on oyster demographics, fishery economics, larval transport, 3D water quality, and oyster filtration. The iterative process of multiple meetings with stakeholders and scientists ensures that the model includes and focuses on the outcomes most important to the stakeholders and that it can forecast outcomes of alternative management strategies that the stakeholders propose. This presentation will provide an overview of the OysterFutures process, a description of spatially-explicit simulation model, and discussion of the potential for this process to improve natural resource sustainability and management.

Collaborators who worked on various aspects of this work: Michael Wilberg, Jeff Blair, Robert Jones, Chris Hayes, Lisa Wainger, Jeffrey Cornwell, Matthew Damiano, Rasika Gawde, Taylor Goelz, Troy Hartley, Raleigh Hood, Melanie Jackson

John Wiedenmann, Rutgers University

Title: Dealing with Uncertainty in the Assessment and Management of Northeast US Fish Stocks

Fisheries managers must balance the tradeoffs of maximizing yield while minimizing the risk of overfishing. In the US, recent changes in federal fisheries legislation require fisheries managers to explicitly consider uncertainty when setting harvest limits. Here, I compare results from two studies exploring uncertainty in the assessment and management of fish stocks in the northeast U.S. The first study developed a simulation model to evaluate harvest policies in use or considered for use by the Mid-Atlantic and New England fisheries management councils. In general, the harvest policies performed similarly, and met a range of fishery objectives such as limiting overfishing and allowing for sizeable long-term yield. In a subsequent study, however, a retrospective analysis of the performance of the New England harvest policy revealed consistently high rates of overfishing for the majority of groundfish stocks in the region (cod, haddock, flounders, etc.). Assessments for New England groundfish frequently overestimated terminal biomass, and as a result of this estimation bias, the buffer in the existing harvest policy has been insufficient to prevent overfishing for groundfish. These findings emphasize the need to explicitly consider historical assessment performance to identify patterns and potential sources of bias so they may be included in future simulation model to better test the performance of alternative harvest policies.

Collaborators who worked on various aspects of this work: Mike Wilberg, Chesapeake Biological Lab, UMCES; Tom Miller, Chesapeake Biological Lab, UMCES; Andrea Sylvia, Iowa State University; and Olaf Jensen, Rutgers University

Michal Wilberg, University of Maryland

Title: Using Population Models to Estimate Abundance of Oyster and Sustainable Fishing Mortality Rates in Chesapeake Bay

Autogenic ecosystem engineers are critically important parts of many marine and estuarine systems because of their substantial effect on ecosystem services. Oysters are of particular importance because of their capacity to modify coastal and estuarine habitats and the highly degraded status of their habitats worldwide. The fishery for eastern oyster (Crassostrea virginica) in Chesapeake Bay was the biggest oyster fishery in the world and the largest fishery in the U.S. in the late 1800s. The population has declined substantially because of overfishing, disease, and habitat loss. We developed a statistical model to simultaneously estimate effects of fishing and disease on oysters in upper Chesapeake Bay during 1980-2009. We compared the model estimates of abundance in 2009 to that prior to large-scale commercial fishing. We found that oyster abundance declined 99.7% (90% credibility interval (CI), 98.3-99.9%) since the early 1800s and 92% (90% CI, 84.6-94.7%) since 1980. Habitat area declined nearly 70% (90% CI, 36.2-83.3%) during 1980-2009. Natural mortality (mortality from all non-fishing sources) of market-sized oysters varied substantially and increased during 1986-1987 and 2000-2002, and natural mortality of small oysters approximately doubled after 1986. The exploitation rate varied over time and averaged 25.1% year-1 (90% CI, 16.1-33.1%) during 1980-2008. We developed a linked population and habitat model for autogenic ecosystem engineers undergoing exploitation. We parameterized the model to represent eastern oyster in upper Chesapeake Bay by selecting sets of parameter values that matched observed rates of change in abundance and habitat. We used the model to evaluate the effects of a range of management and restoration options including sustainability of historical fishing pressure, effectiveness of a newly enacted sanctuary program, and relative performance of two restoration approaches. In general, autogenic ecosystem engineers are expected to be substantially less resilient to fishing than an equivalent species that does not rely on itself for habitat. Historical fishing mortality rates in upper Chesapeake Bay for oysters were above the levels that would lead to extirpation. Reductions in fishing or closure of the fishery were projected to lead to long-term increases in abundance and habitat. For fisheries to become sustainable outside of sanctuaries, a substantial larval subsidy would be required from oysters within sanctuaries. Restoration efforts using high-relief reefs were predicted to allow recovery within a shorter period of time than low-relief reefs. Models such as ours, that allow for feedbacks between population and habitat dynamics, can be effective tools for guiding management and restoration of autogenic ecosystem engineers.

Najat Ziyadi, Morgan State University

Title: Sensitivity Analysis of a Nutrients-Phytoplankton-Oysters (NPO) Mathematical Model of a Bay Ecosystem

In this talk, we will introduce a parametrized mathematical model that is based on a chemostat model and use it to theoretically describe the interactions of nutrients (N), phytoplankton (P) and oysters (O) in a bay ecosystem. Using the theoretical Model (NPO), we will derive verifiable conditions for the persistence or extinction of phytoplankton and oysters in a bay ecosystem. In addition, we will use local and global sensitivity analysis and simulations to illustrate how human activities such as increased oyster harvesting and environmental factors such as increased nutrients flow and increased oyster filtration can generate phytoplankton blooms via Hopf bifurcation with corresponding oscillations in the oyster biomass and nutrients level in a bay ecosystem. Authors: Dr. Kelton Clark, Patuxent Environmental and Aquatic Research Laboratory, Morgan State University
Dr. Chunlei Fan, Department of Biology, Morgan State University
Dr. Asamoah Nkwanta, Department of Mathematics, Morgan State University
Dr. Najat Ziyadi*, Department of Mathematics, Morgan State University

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Document last modified on August 24, 2017.