Ship Shoal: Sand, Shrimp, and Seatrout (GM-92-42-109)

MMS ENVIRONMENTAL STUDIES PROGRAM: ONGOING STUDIES
MMS OCS Region:	Gulf of Mexico
Title:	Ship Shoal: Sand, Shrimp, and Seatrout (GM-92-42-109)
Planning Area:	Central
Total Cost: $145,778	Period of Performance: FY 2004-2009
Conducting Organization:	Coastal Marine Institute, Louisiana State University
MMS Contact:	Colleen Finnegan
Description: Background: MMS is addressing the recent demand for long-term use of US continental shelf sand resources for coastal erosion management, a critical challenge to Louisiana’s ecosystems and economies. Louisiana considers barrier island restoration as a promising way to combat wetland loss with sand mined from Ship Shoal as the most feasible sediment source. Ship Shoal supports major demersal fisheries that may be directly impacted by Ship Shoal sand mining. These fisheries target white and brown shrimp (shrimp) and spotted seatrout (seatrout). These species are major components of the Ship Shoal ecosystem. White and brown shrimp are opportunistic benthic-feeding omnivores. Spotted seatrout are important predators on white and brown shrimp. Given the national importance of these fisheries and the constraints in which they operate, negative impacts of sand mining on these directed fisheries would have far reaching implications. Atlantic croaker (croaker) is an abundant demersal predator in the Ship Shoal area with at least three close shrimp/spotted seatrout associations. First, croaker competes with spotted seatrout for shrimp as prey and croaker competes with shrimp for other benthic prey. Second, croaker is impacted as bycatch in the area’s shrimp and seatrout fisheries. And third, croaker support important recreational fisheries in other areas less rich in spotted seatrout. As such Atlantic croaker is a logical indicator species of change in the shrimp and spotted seatrout carrying capacity of the Ship Shoal area and may support a future directed fisheries in this area. During the shrimp-directed trawling efforts, unexpected and persistent concentrations of spawning, hatching, and foraging female blue crabs were found in the study area. MMS funding allowed a broadening of the study area to include an analysis of blue crab populations. An assessment of the benthic feeding ecology of these five fishery resources (white and brown shrimp, spotted seatrout, Atlantic croaker, and blue crab) is required to evaluate potential impacts of sand mining from Ship Shoal.
Objectives: The objectives of this study are to provide information to assess the possible biological effects of long-term dredging on Ship Shoal by answering the following questions: Are white and/or brown shrimp populations more concentrated at Ship Shoal as compared to non-shoal areas? Are spotted seatrout and Atlantic croaker populations more concentrated at Ship Shoal as compared to non-shoal areas? Are blue crab populations more concentrated at Ship Shoal as compared to non-shoal areas? Does the sex ratio, stage of maturation, mean size, and/or condition factor of these fishery resources differ between Ship Shoal and non-shoal areas independent of the effects of season, water depth, and/or year? What is the dominant prey species found in the guts of these organisms? Are the gut content patterns of these four fishery resources different between Ship Shoal and non-shoal areas? If so, do these differences reflect known prey preferences for sandy substrate? Are non-shoal areas likely to serve as alternative foraging and maturing habitats for these four fishery resources during periods of sand removal from Ship Shoal and/or during recolonization of the borrow sites?
Methods: Acquire historic, fishery independent, relevant data on these four fishery resources in the Ship Shoal area and from comparison (non-Ship Shoal) sites from the Louisiana Department of Wildlife and Fisheries (LDWF) for their LDWF LOOP and LDWF SEAMAP cruises. Computerize and verify the uncomputerized portions of the LDWF SEAMAP data. Assess statistical distributions of parameters to be used in this study. Collect site-specific specimens (from the Ship Shoal area and non-shoal sites) of white shrimp, brown shrimp, Atlantic croaker, spotted seatrout, and blue crabs from upcoming LDWF SEAMAP summer, fall, and winter groundfish/shrimp cruises to be. Measure and dissect these specimens for new, needed, and compatible data on stage of maturation, condition factor, and gut contents of these species. Computerize, verify and integrate data. Collect site-specific catch/effort data on and carcasses of spotted seatrout for the Ship Shoal area and a non-shoal site from five cooperating recreational anglers through the Coastal Conservation Association of Louisiana. Measure and dissect these specimens for new, needed, and compatible data on gonadal condition, length, and gut contents of these fish.
Products: Quarterly and annual progress reports; final technical report; computerized biological dataset on CD-ROM for input to ARC GIS system.
Importance to MMS: The State of Louisiana has been, and will continue to, request negotiated agreements from the MMS to use Ship Shoal as a source of sand for planned barrier island and coastal nourishment activities. Ship Shoal is the only viable, compatible, large-scale source of sand for planned Louisiana barrier island/barrier shoreline restoration and nourishment. The information provided by this study will be used to assess the biological impacts associated with large-scale removal of sand from Ship Shoal. This assessment will be used to evaluate future requests for negotiated agreements.
Current Status: Several cruises have now taken place and pre-dredging biological samples from the Ship Shoal area have been collected. Two cruises were conducted in conjunction with the Louisiana Wildlife and Fisheries SEAMAP Program in June and October of 2007 and three additional MMS sponsored cruises to Ship, Tiger and Trinity shoals were made collect samples and physical data in April, August and October. The PI has coordinated with the USGS-Biological Resources Division to obtain samples collected from their cruises conducted as a component of the USGS/MMS Ship Shoal dredging impact study. This project is being conducted in close association with the Louisiana Sand Management Group (through active participation/presentations its meetings and discussions) and with the two other current MMS/DNR Ship Shoal projects. The Primary Investigators made a presentation at the December 2006 3rd National Restore America’s Estuaries Conference (http://www.estuaries.org/) and presented their research in a session at the 2008 Ocean Sciences meeting in Orlando, FL. Most recently the Primary Investigators delivered a presentation at the Annual MMS ITM Meeting in January of 2009 in New Orleans, LA. While the white shrimp findings continue to denote a critical role for shoal in the life cycle of this economically important species, the combined projects are also strongly suggesting the importance of Ship Shoal in the resilience of the surrounding Gulf of Mexico and an unexpected offshore spawning ground for commercially important blue crabs, as discussed in the following two paragraphs. In relationship to systems integrity, Ship Shoal can now be viewed as a shallow, oxygen-rich “island” surrounded by deeper muddy deposits prone to hypoxia. Using polychaetes to initially characterize differences between assemblages on the shoal and off the shoal, LSU is finding that species richness is much higher on the shoal than previously found in the surrounding area. For example, the composition of the polychaete assemblages on the shoal appear to be unique to the area, notably because of the presence of species – i.e. Phyllodoce mucosa or Nephtys simoni – previously found only in the most eastern part of the Gulf of Mexico. And, the shoal polychaete community is also characterized by the high diversity of spionids – i.e. 13 species – known to be opportunistic species. Polychaete assemblages showed a slight east-west gradient. East assemblages are characterized by Spiophanes bombyx, Dispio uncinata, Mediomastus californiensis and Magelona sp.A; while the most western part of the shoal was characterized by the additional occurrence of Owenia fusiformis and Tharyx annulosus. A decreasing diversity gradient ranging from the southern to the northern edge of the shoal was superimposed over east-west variations in species composition. These data suggest that shoals may be a source of larval recruits to the Louisiana shelf impacted by seasonal hypoxia. The P. I.s are exploring these results as they relate the feeding ecology of white and brown shrimp on Ship Shoal and in the surrounding offshoal environment, and expanding our analyses to the other dominant marcroinfauna. In 2005 and 2006 an offshore population of spawning Callinectes sapidus, blue crabs, was discovered on Ship Shoal which extends the present knowledge of blue crab spawning dynamics. Prior to these findings, blue crab spawning activity has almost always has been described as occurring in lower estuary, tidal passes and near shore barrier islands in the Gulf and South Atlantic. During the spring and summer of both 2005 and 2006 LSU encountered aggregations of mature female blue crabs on Ship Shoal. Internal and external examination (following our “shrimp procedures’) revealed that these crabs were healthy -- with “full” muscles and either well developed ovaries or developing egg masses on their swimmerets (“in berry”). The similarity in the composition of Ship Shoal’s benthic community, the gut contents of the blue crabs we obtained on Ship Shoal, and the published literature on blue crab feeding support the argument that Ship Shoal is a preferential foraging area for blue crabs. The PIs are currently exploring the implications of these findings in relationship to potential sand mining impacts on spawning blue crab and foraging sea turtles. A draft final report was submitted to MMS in August of 2008. Currently the final report is due to be submitted to MMS and will be placed into MMS GOMR review query. The final date for the completed edited report to be delivered to MMS is awaiting the finalization of a no-cost date extension which is currently pending.
Final Report Due:	October 2008 (No-Cost Date Extension is Pending)
Publications:	None
Affiliated WWW Sites:	http://www.mms.gov/sandandgravel/Louisianastudies.htm
Revised date:	March 2009
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