RESEARCH

Scientists fish for answers in Inland Bays

Marine biology and engineering will join forces to investigate how fluctuating water quality affects young fish, particularly the question of why such fish don’t always swim away from an area when water quality drops.

Timothy Targett, professor of marine biology-biochemistry in the College of Marine Studies, and Dominic Di Toro, Edward C. Davis Professor of Civil and Environmental Engineering, have received a $548,273 grant from the National Oceanic and Atmospheric Administration (NOAA). The three-year grant will support their research to determine the impact of fluctuating water quality on fish that use estuaries and coastal bays as nursery grounds during their first few months of life.

Part of the work will be conducted in two of Delaware’s Inland Bays—Rehoboth and Indian River. During the summer months, these sheltered bays provide valuable nursery habitat for key recreational and commercial fisheries, including summer flounder and weakfish. But, significant reductions in dissolved oxygen levels often occur daily during summer in the tidal tributaries used by young fish as nursery grounds.

According to Targett, scientists do not understand why juvenile fish use these waters in such abundance when low dissolved oxygen can adversely affect their growth and survival. In addition, fish have the ability to swim to other areas where the water quality is better.

“We don’t know why the fish are even in some of these areas,” Targett says. “Is there such a great source of food that they just go in, stay as long as possible, grab some food and then make a run for it?”

To answer this question, Targett and Di Toro will use a unique modeling approach that combines the results of two different models. One model will predict how the water quality changes over space and time. This water-quality model will be constructed using detailed measurements of salinity, temperature and levels of dissolved oxygen in the water.

The second model will link the growth, behavior and survival of an individual fish with changes in these parameters. This individual-based model was developed in previous laboratory and field experiments conducted by Targett. It will be validated in the current study by directly tracking fish movement with acoustic tags in Pepper Creek, a tributary of Indian River Bay.

By joining the two models, the scientists say they can predict the behavior of juvenile fish based on the water quality at a specific location throughout the summer—something that has never been done before. Damian Brady, a doctoral candidate in marine biology-biochemistry, will assist Targett and Di Toro in the research.

The field study in Pepper Creek also will look at the effect of dissolved oxygen on the benthic community as well as the effect that the amount of food has on the response of fish. The benthic community consists of crabs, worms and other marine organisms that live in and on the bottom sediments and provide juvenile fish with food.

This portion of the study will be led by Robert Diaz, professor of marine science at the Virginia Institute of Marine Science. The institute received an additional $135,314 in grant money, bringing the total award to $683,587. Danielle Tuzzolino, a master’s degree student in marine biology-biochemistry will assist Targett and Diaz in completing this work.

“It is truly an integrated and cooperative approach that links marine biology with engineering,” Targett says. “None of us could do this project by ourselves. In particular, Damian has been very instrumental in bridging this gap by taking modeling courses from Dominic in addition to his courses in marine sciences.”

Targett says the research is designed to provide fisheries managers with a tool that predicts the impact of changing water quality on the growth and survival of juvenile weakfish and summer flounder. In addition, the modeling approach is not site specific, but can be applied to many other coastal ecosystems.

Specifically, the research will address how various scenarios that affect water quality  influence the behavior of juvenile fish. This information will enable fisheries managers to minimize the adverse effects that a project might have on the marine environment.

“The results will help management officials spend money where it is needed the most,” Di Toro says. “It can cost a lot of money to improve the water quality once it has been degraded, and you don’t want to spend money to correct something that isn’t really a problem to begin with.”  

— Kari Gulbrandsen, EG ’91M