Investigators: Drs. Aaron Carlisle, George Parsons, Edward Hale

Recreational fishing is an important economic activity in coastal states such as Delaware, and sharks are commonly targeted by recreational fisheries. Recently, charter fishing vessels have begun to increasingly target sharks, however, the impact of these fisheries remain unquantified from a biological (i.e., post-release mortality) and economic (i.e., how much revenue does shark fishing bring to local economies) perspective. Hence the biological and ecological impacts of recreational fisheries on local shark species and associated economic value of sharks to the Delaware economy have almost certainly been underestimated.

Fundamental to understanding the impacts of recreational angling on shark species is understanding how anglers interact with sharks (what species, how often, how do they handle them, etc.) and how these interactions impact the health of sharks, as even released sharks commonly exhibit post-release mortality, at times as high as 50%. Further, to effectively manage recreational fisheries and understand their role in coastal communities, an understanding of the economic value of the resource is needed.

To these ends, we propose to conduct an interdisciplinary study to characterize the biological and economic impact of recreational shark fisheries in Delaware. Our proposal has three major objectives: 1) characterize the stress physiology and post release mortality of shark species commonly caught by recreational anglers (led by Dr. Carlisle), 2) describe the recreational shark fishery in Delaware (led by Dr. Hale), and 3) quantify the economic value of sharks to the Delaware economy through recreational fishing, tourism, and other activities (led Dr. Parsons).

Investigators: Jonathan H. Cohen, Kimberly L. Oremus, Anna M. Birkenbach

Delaware's 100-year-old commercial blue crab fishery is embedded in the state’s identity and economy, producing three times the revenue of all the state’s other commercial fisheries combined. Climate change and other environmental stressors pose a growing threat to this valuable state resource.

While recent literature indicates that higher reproductive capacity can mitigate the effects of extreme environmental fluctuations on the fishery, resiliency of the blue crab population may be hampered by sperm limitation resulting from the harvest of large male crabs.

This project will determine whether sperm limitation is occurring by measuring stored sperm quantity and quality over the year in Delaware Bay female crabs, along with the operational sex ratio. These will parameterize a monthly population dynamic model. The biological outcomes will be linked to alternative management strategies aimed at increasing the availability of larger male crabs. Using a bioeconomic model, we will project the economic and population impacts of each alternative management strategy for the commercial fishery.

This project seeks to improve the parameterization of Delaware Department of Natural Resources and Environmental Control’s blue crab stock assessment models, propose actionable policy buffers to mitigate large uncertainties and environmental variability, and inform Delaware's Shellfish Advisory Council’s future policy decisions.

Investigators: Drs. Aaron Carlisle and Edward Hale

As apex predators, Sandbar and Sand Tiger Sharks play an important role in the Delaware Bay ecosystem, impacting food web structure and function directly through feeding and indirectly through changing the behaviors of potential prey. These ecological effects will influence the abundance and fitness of managed species with economic implications for commercial and recreational fisheries. Furthermore, recreational fishing for sharks is becoming an increasingly important component of the coastal economy. Hence, sharks will have a variety of potentially important effects on the Delaware Bay food web and the ecosystem services it provides to the local economy although these effects remain unknown and unquantified.

This study proposes to characterize the trophic ecology of the Sandbar and Sand Tiger Shark to understand the ecological role they play in the Delaware Bay ecosystem, quantify the potential impact they have on managed species, and improve ecosystem management. The project will use a combination of approaches to characterize the diet and trophic ecology of sharks, including stomach content analysis as well as stable isotope analysis, which uses the chemical composition of the sharks and their potential prey to understand their diet. By comparing shark consumption estimates to commercial and recreational landings, this research will be able to estimate the relative economic impact of shark predation assuming that managed species consumed by sharks are unavailable to fisheries and consumption of forage species reduces the prey base for managed species.

Investigators: Drs. Shawn W. Polson, K. Eric Wommack, and Patrick Gaffney

The eastern or American oyster, Crassostrea virginica, is a keystone species in coastal ecosystems along the east coast of North America. The ecosystem services this species provides have been severely reduced over the past centurythrough overharvesting, habitat degradation, and the emergence of lethal diseases. This study will assess the microbiome of natural and restored populations in order to determine the impact commensal microorganisms have on the success of the eastern oyster.

Healthy oyster populations are ecologically important as their filter-feeding activities consume plankton and help to clarify the water where they live. Oysters are also economically important as oyster harvesting and aquaculture provides jobs and revenue to coastal communities.

Regrettably, these important services have been severely reduced over the past century, first through overharvesting and habitat degradation, and more recently from the emergence of lethal diseases that kill significant proportions of infected adult oysters each year. An emerging field of research has begun to look at entire communities of microorganisms (the microbiome) that are associated with a host animal. An essential question driving this research area has been the role the microbiome plays in the health and disease of its host animal. For example, we now know that specific bacterial communities within the gut are associated with obesity in humans. Thus, the physiology of an oyster “holobiont” is very likely due to a complex interplay of the animal and its associated microbiome.

This study will assess the microbiome of natural and restored populations, and maricultural bred lines of C. virginica. We will also investigate whether the genetic make-up of an individual oyster (the oyster genotype) influences its microbiome by examining both wild oysters and oysters that have been bred for disease-resistance. We will accomplish these goals by leveraging cutting-edge DNA sequencing technology to obtain detailed views of the oyster holobiont, including the individual oyster genotype and its associated bacterial and viral microbiome. With the help of the Delaware Sea Grant Marine Advisory Service and the Center for the Inland Bays, fieldwork will be conducted over an annual cycle in the Delaware Bay and the Delaware Inland Bays.

In particular, our scientific objectives are:

Obj. I) Through a seasonal survey, establish baseline commensal microbial (viral and bacterial) communities within oysters from natural and restored populations in the Delaware Bay and Inland Bays.

Obj. II) Compare commensal microbial communities between natural and maricultured oysters, including disease-resistant oyster lines.

Obj. III) Investigate linkages between the composition of oyster commensal microbial communities and oyster genotype.

It is our hope that this fundamental research will lead to new maricultural approaches for improving oyster health and to controlling or preventing lethal oyster diseases. Ultimately, achieving these goals will help to ensure the ecological and economic benefits of oysters for coastal communities.

Investigator: Dr. Dennis McIntosh

To improve seafood safety, post-harvest processing of shellfish is becoming the industry standard. Delaware Sea Grant is funding a mini-grant to test new depuration (cleansing or purification) or post-harvest treatment of bivalve shellfish. Two related proprietary disinfecting technologies, alone and in combination, are being compared to conventional ultraviolet disinfection. Researchers are exploring suitability for use on live shellfish in an early exploratory phase of this research.