Grantee Research Project Results

1998 Progress Report: Spatial and Temporal Environmental Variation in a Eutrophic Coastal River: Impacts on Fish and Marine Mammals

EPA Grant Number: R826100
Title: Spatial and Temporal Environmental Variation in a Eutrophic Coastal River: Impacts on Fish and Marine Mammals
Investigators: Crowder, Larry B. , Read, Andrew J.
Institution: Duke University
EPA Project Officer: Hahn, Intaek
Project Period: October 20, 1997 through October 19, 2000
Project Period Covered by this Report: October 20, 1997 through October 19, 1998
Project Amount: $357,262
RFA: Exploratory Research - Environmental Biology (1997) RFA Text |  Recipients Lists
Research Category: Aquatic Ecosystems , Biology/Life Sciences

Objective:

Human activities in estuarine watersheds have contributed to an increase in nutrient loading and associated water quality declines, habitat loss, and declining fisheries. Recent algal blooms in the Neuse River estuary, NC have led to its designation as one of the top 20 most threatened river systems in the U.S.. We are examining distributions of fishes and marine mammals in the Neuse in relation to temporal and spatial dynamics of water quality. In particular, we seek to understand the effects of episodic hypoxic or anoxic events. These events can affect highly visible and economically valuable components of the estuarine food web. Mobile fishes likely move out of hypoxic areas, but may become trapped if these hypoxic zones expand into oxygenated waters. Bottlenose dolphins (Tursiops truncatus) can tolerate a wider range of water quality than fishes, but their distribution is likely to be tied closely to that of their prey. We hypothesized that: (1) distribution and composition of fish communities will respond to spatial and temporal changes in temperature, salinity, and extent of hypoxia in estuarine systems; and (2) the distribution of bottlenose dolphins will respond to changes in the distribution of their prey caused by changes in water quality.

Progress Summary:

Distribution and Community Structure of Fish
To assess how fish distribution and community structure changes with water quality conditions, we monitored two different study sites on the Neuse River estuary: an 'upstream' and a 'downstream' study area. The downstream site was sampled biweekly, while the upstream area was sampled monthly. We encountered hypoxia often enough to examine how fish distribution changes in response to low oxygen. Fish were not typically found in waters with dissolved oxygen levels less than 2.0 mg/l. Results from categorical and regression trees are being used to examine species-specific changes in catch as oxygen levels increase. Preliminary results from the 1998 data demonstrate a decrease in both number of species captured and Shannon-Weaver diversity index with reduced dissolved oxygen concentration. Unfortunately, seasonal trends in diversity and abundance confound our ability to examine how diversity changes with habitat loss within a year. Multi-year data may allow us to make these comparisons.

Distribution of Bottlenose Dolphins
For our study of habitat use patterns of bottlenose dolphins, we surveyed a 472-km2 area of the Neuse River estuary. The dolphin study area encompassed both the upstream and downstream sites monitored for the study of fish distribution. Once a group of dolphins was sighted during our survey, we chose an easily recognizable "focal animal" from that group and recorded its movements and behavior using a three-minute point sampling protocol. During our focal animal follows, we recorded water quality data (dissolved oxygen, salinity, temperature, and depth) every 30 minutes, and we sampled the fish community every 60 minutes with an otter trawl.

From May to October 1998, we conducted 43 vessel-based dolphin surveys. We encountered groups of dolphins during 30 surveys. The mean group size was 19.5 dolphins. From our 30 sightings, we had 21 focal animal follows that lasted more than 0.5 hours (mean duration = 3.1 hours). Dolphins used the nearshore waters of the Neuse (<2.5 m depth) and lateral creeks much more than the open waters of the mid-river (>2.5 m). Dolphins used the lower half of the study area much more extensively than the upper half; only two sightings occurred upstream of Adams Creek. Few dolphins were sighted in the spring and early summer, but sightings increased throughout the summer. Analysis of photoidentification data is still ongoing, but thus far we have identified 144 individual dolphins in the Neuse River.

Description of Diet of Bottlenose Dolphin
We have completed preliminary analysis (dissection, identifying and measuring intact food items, and cleaning and identifying skeletal parts from well-digested food items) of the stomach contents of 61 bottlenose dolphins that were stranded or killed incidentally in commercial fishing operations. Sea trout (Cynoscion spp.), Atlantic croaker (Micropogonias undulatus), spot (Leiostomus xanthurus), silver perch (Bairdiella chrysoura), pinfish (Lagodon rhomboides), and striped mullet (Mugil cephalus) appear to comprise the bulk of the diet of coastal bottlenose dolphins in North Carolina.

Journal Articles:

No journal articles submitted with this report: View all 3 publications for this project

Supplemental Keywords:

Anoxia, Bottlenose Dolphin, Estuary, Eutrophication, Hypoxia, Neuse River, Tursiops truncatus, Water Quality, Estuarine Fishes., RFA, Ecosystem Protection/Environmental Exposure & Risk, Scientific Discipline, Water, Ecological Indicators, Ecological Risk Assessment, Ecosystem Protection, Watersheds, Ecosystem/Assessment/Indicators, Oceanography, exploratory research environmental biology, Ecological Effects - Environmental Exposure & Risk, Nutrients, Water & Watershed, Ecology and Ecosystems, Environmental Monitoring, ecological effects, watershed management, bottlenose dolphins, mammal, water quality, coastal ecosystem, ecological assessment, eutrophication, ecological exposure, bottlenose dolphin, food web, nutrient fluxes, algal growth, fisheries, land use, aquatic ecosystems, fish , landscape indicator, anoxia/hypoxia, nutrient transport, marine ecosystem

Relevant Websites:

Water Resources Research Institute at North Carolina State University:
http://www2.ncsu.edu/ncsu/CIL/WRRI/index.html

Neuse River Home Page:
http://www2.ncsu.edu/ncsu/CIL/WRRI/neuse.html

American Fisheries Society Home Page:
http://www.fisheries.org/

Society for Marine Mammalogy Home Page:
http://pegasus.cc.ucf.edu/~smm/

Progress and Final Reports:

Original Abstract

1999

Final