By Hailey Murphy, S.C. Sea Grant Consortium.
SCDNR researchers on the R/V Silver Crescent collecting samples of white shrimp like those included in annual reproductive assessments. Photo courtesy of SCDNR.
When you think of South Carolina, you think of shrimp. This may be because the commercial shrimp fishery is consistently ranked among the top three fisheries in the state in terms of landings and value. Inspiring festivals, endless recipes, and a beloved maritime tradition, shrimp play an important role in South Carolina’s history, culture, and cuisine.
To protect this resource, the S.C. Department of Natural Resources (SCDNR) opens state waters to commercial trawling based on the abundance and reproductive status of our most economically valuable penaeid shrimp species, the white shrimp (Penaeus setiferus). White shrimp typically spawn—or reproduce by making eggs, or roe—between spring and early summer, depending on the water temperature. In a typical year, most reproduce before June under ideal environmental conditions. Each spring, the commercial roe white shrimp season opens if SCDNR biologists find that most adult female white shrimp sampled have already spawned, indicating that enough shrimp have reproduced to support a strong fall harvest.
In addition to fishery-independent sampling by SCDNR, researchers collect samples onboard commercial trawlers in the spring to identify the stage of reproduction of adult female white shrimp through two methods. In the field, they look at the ovaries, which are visible through the carapace. As the shrimp progress through their reproductive cycle, changes in the shape, texture, size, and color of the ovaries allow researchers to assign specimens to a particular stage of ovarian development. Historically, five stages of development have been used; however, this method is imperfect due to the similarity of visual indicators between a shrimp that is preparing to spawn and one that has recently spawned. The second, more time-consuming method is to collect samples of shrimp, dissect them to remove and preserve the ovaries, and then confirm the shrimp’s reproductive status in the lab by analyzing the ovaries under a microscope.
Close up of a white shrimp, Penaeus setiferus, one of three native species of penaeid shrimp found wild in South Carolina. Photo courtesy of SCDNR.
This is the focus of a Consortium-funded research project, “Refining Assessments of Reproductive Activity in White Shrimp (Penaeus setiferus) to Improve Management Decisions,” led by Principal Investigator (PI) Michael Kendrick, Ph.D., at SCDNR Marine Resources Research Institute (MRRI). The project aimed to support the fishery by creating an enhanced visual guide to more reliably identify the reproductive status of white shrimp in the field macroscopically—without the use of a microscope—and develop a more complete understanding of the impact of water temperature and other environmental factors on the timing of reproductive development in white shrimp in the South Carolina–Georgia coastal region.
Co-Investigators, Project Partners, and Graduate Student Researchers include:
- Peter Kingsley-Smith, Ph.D., SCDNR Marine Resources Research Institute.
- Jeff Brunson, SCDNR Office of Fisheries Management.
- Chris McDonough, SCDNR Office of Fisheries Management.
- Graham Wagner, SCDNR Marine Resources Research Institute.
- Alexandra C. Mitchell, SCDNR Marine Resources Research Institute; recent M.S. recipient from the College of Charleston.
Sampling locations for macroscopic and microscopic reproductive assessments of white shrimp in S.C. (circles) and GA (triangles). Map courtesy of SCDNR.
The research team began sampling white shrimp from mid-March through mid-June of 2022, in the Charleston Harbor and near-shore oceanic waters, collecting a total of 516 adult female white shrimp. Each shrimp was tested both macroscopically in the field with photographic documentation, as well as microscopically. Microscopic analysis resulted in a publication in the Journal of Crustacean Biology, 2024, entitled “Characterizing reproductive development in female white shrimp Penaeus setiferus (Decapoda: Dendrobranchiata: Penaeidae) in South Carolina, USA” by former graduate research assistant Alexandra C. Mitchell, who is now a wildlife biologist with SCDNR.
The team tested for significant differences between the field observations and the microscopic approach to ovarian development categorization. When comparing the assessments of white shrimp ovarian tissues in Charleston Harbor, the agreement between the two approaches declined as the spawning season progressed from April to June.
These results informed the standardization of a new visual guide to macroscopically categorize white shrimp reproduction. The utility of this guide for categorizing ovary development in white shrimp was then tested on a regional scale and distributed through the Georgia Department of Natural Resources (GADNR) and the N.C. Division of Marine Fisheries.
Updated macroscopic guide to the five stages of female white shrimp ovarian development. Immature and early developing female white shrimp have translucent ovaries (1 and 2), which become milky and then take on a yellow color as ovaries develop (3). When shrimp are spawning capable, their ovaries become olive or green in color (4). After spawning, the ovary again appears milky or mildly opaque (5). Graphic courtesy of SCDNR.
To field-test the visual guide and to document differences in geographic data for the onset of reproductive activity, SCDNR coordinated with GADNR’s Ecological Monitoring Trawl Survey (EMTS) to intensively sample representative areas of the entire coast of S.C. and GA from April 2–5, 2024. In total, 587 female white shrimp were collected across six estuaries in S.C. and six estuaries in GA.
These samples provided data on the biological indicators of reproduction in white shrimp across a range of locations along a latitude line—running North-to-South or South-to-North—which provides fisheries managers with detailed descriptions of how the timing of reproductive activity may differ latitudinally across the South Carolina–Georgia coast.
The team also investigated trends in the timing of female reproductive development and its relationship with environmental conditions using existing datasets from the Southeast region spanning 1979–2023. These datasets included fisheries-dependent data collected by commercial shrimp vessels, and fisheries-independent data collected as part of monitoring surveys of both estuarine (SCDNR’s Estuarine Trawl Survey, ETS) and coastal (SCDNR’s SEAMAP survey) waters. Analyses revealed significant trends of earlier spawning onset by 4–5 days per decade, driven in part by warming waters.
“This project improved our understanding of white shrimp reproduction at the cellular level and combined historical data with modern sampling to explore how environmental conditions influence the valuable crop of spring roe shrimp,” said PI Michael Kendrick, Ph.D.
Learn more about shrimp in South Carolina and find recreational harvest information in this guide to crustaceans and shellfish regulations.
For questions related to this research project, reach out to PI Michael Kendrick, Ph.D., at SCDNR’s Marine Resources Research Institute. For questions related to the commercial shrimp fishery, reach out to co-PI Jeff Brunson.