ACCESS NUMBER: 30660-19962 

STUDY TITLE: Potential Spatial and Temporal Vulnerability of Pelagic Fish Assemblages in 

the Gulf of Mexico to Surface Oil Spills Associated with Deepwater Petroleum Development 

REPORT TITLE: Potential Spatial and Temporal Vulnerability of Pelagic Fish Assemblages in 

the Gulf of Mexico to Surface Oil Spills Associated with Deepwater Petroleum Development 

CONTRACT NUMBER: 14-35-0001-30660-19962 

SPONSORING OCS REGION: Gulf of Mexico 

APPLICABLE PLANNING AREAS: Eastern Gulf of Mexico, Central Gulf of Mexico, Western 

Gulf of Mexico 

FISCAL YEARS OF PROJECT FUNDING: 1998 

COMPLETION DATE OF REPORT: March 2005 

COSTS: FY: 1998: $59,056 

PROJECT MANAGER: M.C. Benfield 

AFFILIATION: Louisiana State University, Coastal Fisheries Institute 

ADDRESS: 2179 Energy, Coast and Environment Building, Baton Rouge, LA 70803 

PRINCIPAL INVESTIGATORS: M.C. Benfield and R.F. Shaw 

KEY WORDS: pelagic fishes, adults, larval stages, Gulf of Mexico Region, spatial distributions, 

tuna, Thunnus albacares, Thunnus thynnus, Thunnus atlanticus, marlin, Makaira nigricans, 

Tetrapturus albidus, wahoo, Acanthocybium solanderi, dolphinfish, Coryphaena hippurus, blue 

runner, Caranx crysos, ocean sunfish, Mola mola, flying fish, Cypselurus furcatus, Cypselurus 

melanurus, Sargassum, sargassumfish, Histrio histrio, filefish, Monocanthus hispidus, tripletails, 

Lobotes surinamensis

BACKGROUND: As petroleum exploration expands into, and beyond the waters of the OCS, 

the potential exists, via accidental spills, to adversely impact pelagic recreational and 

commercial fisheries. Surface petroleum spills in pelagic waters of the OCS will primarily impact 

those species of fishes and crustaceans that inhabit the epipelagic zone of the open ocean. 

Members of this group include several species that command a high monetary and socioeconomic value, as well as ecologically important or indicator species. Spills in the surface 

waters are also likely to impact floating Sargassum communities, which contain a diverse and 

often unique faunal assemblage of fishes and invertebrates and which also serve as important 

nursery habitats for many fishes. Relatively little is known about the susceptibility of pelagic 

fishes from the Gulf of Mexico OCS to petrochemical spills. The magnitude of any impact will 

depend upon the spatial and temporal scale of the incident as well as the chemical properties of 

the spilled material. The spatial scale (location, depth and extent) of the spill combined with the 

temporal scale (timing and duration) will combine to determine the species and life history 

stages that are likely to be present in the impacted area. Unfortunately, information on the 

spatial and temporal distributions of pelagic fish stocks in the OCS is not readily available and is 

generally scattered throughout the peer-reviewed and non-peer-reviewed technical literature 

and databases. 
ACCESS NUMBER: 30660-19962 

OBJECTIVES: This study was undertaken to synthesize what is known about the spatiotemporal distribution patterns of selected pelagic fish species. We have attempted to provide an 

estimate of what life history stages of these target species are likely to be present within the 

OCS waters on a seasonal (monthly) basis. 

DESCRIPTION: We delineated a study region of the north central Gulf of Mexico that includes 

waters above the 200-2000 m isobaths south to 26 oN latitude. The study area was divided into 

four zones: western zone (96.4 oW–92.0 oW, 26.0 oN–28.0 oN), central zone (92.0 oW–88.0 oW, 

26 oN–28 oN), eastern zone (88 oW–84.3 oW, 26.0 oN–28.0 oN), and a triangular northern zone 

with a base from 90.7 oW-84.3 oW at 28 oN, and an apex at 87 oW, 30 oN (Fig. 1). The western, 

central and eastern zones correspond broadly to the MMS western, central and eastern 

planning areas. Species selected for study were: bluefin tuna (Thunnus thynnus), yellowfin tuna 

(T. albacares), blackfin tuna (T. atlanticus), blue marlin (Makaira nigricans), white marlin 

(Tetrapturus albidus), wahoo (Acanthocybium solanderi), dolphinfish (Coryphaena hippurus), 

two species of flyingfishes: Cypselurus melanurus and C. furcatus, blue runner (Caranx crysos), 

Ocean sunfish (Mola mola), and Sargassum community fauna: sargassumfish (Histrio histrio), 

planehead filefish (Monocanthus hispidus), tripletails (Lobotes surinamensis). 

In addition to a comprehensive literature search of the available peer-reviewed literature, gray 

literature (Table 1), and Internet websites, this report drew heavily on two datasets: the National 

Marine Fisheries Service (NMFS) long-line database and the Southeast Area Monitoring and 

Assessment Program (SEAMAP) ichthyoplankton surveys. Reported observations were sorted 

by month into a 10’ longitude by 10’ latitude grid (approximately 100 nautical miles2

 or 343 km2). 

The potential presence of a particular stage in any of the cells within the grid was ranked 

according to three categories: confirmed, reasonable inference, and unreported. Confirmed 

presence was assigned when a physical sample of the relevant stage of a particular taxon had 

been reported as being present within a cell. Reasonable inference was assigned to any cells 

within which, there was no confirmed presence, providing the cells were located within a radius 

of two cell distances (for adults) or one cell distance (for larvae/juveniles) of a cell with a 

confirmed presence. Reasonable inference was also assigned to any cells that were bounded 

by four or more cells also designated with the reasonable inference category. Finally, any 

regions within the study area that were completely surrounded by cells designated as confirmed 

or reasonable inference were also assigned reasonable inference. Finally, all cells that did not 

fall into the confirmed or reasonable were assigned an unreported category. 

SIGNIFICANT CONCLUSIONS: For each species, we have summarized the available 

distributional data on a monthly basis and have attempted to predict the distributions of larvae, 

adults, and juveniles (when possible) within the study region. Companion software in the form 

of Microsoft Excel spreadsheets allow the user to query the data to obtain probable distributions 

within specific locations defined by their longitude and latitude. It is clear that for many taxa, 

substantial gaps exist in our understanding of their spatial and temporal distributions. Prediction 

of the distributions of larvae and juveniles is particularly problematic due to the limited amount of 

spatially explicit data available for these life history stages. Estimation of vertical distributions 

was also problematic for most stages and taxa. 

STUDY RESULTS: Distributional data are predicted for each month for adults and 

larvae/juveniles where possible. An example of these results is provided for yellowfin tuna. 

Comparable predictions are provided in the report, but are not summarized here, for the other 

taxa in the study. 
ACCESS NUMBER: 30660-19962 

Adult yellowfin tuna are likely present throughout the majority of the study area during all 

months of the year. During winter, the majority of confirmed landings were in the western and 

western halves of the central and northern zones. By April, yellowfin expand their distribution in 

the northern zone towards the northeast and this movement pattern continues through May and 

June. During April there is also an apparent movement into waters deeper than 200 m in the 

southeastern edge of the northern zone and the northeastern edge of the eastern zone. In 

summer, adults are present throughout most of the three zones and during fall and early winter, 

the epicenter of confirmed records shifts back to the western and central zones. The SEAMAP 

dataset contains extremely limited numbers of confirmed yellowfin larvae that were only present 

during May and June. Predictions of larval distributions based on this dataset are restricted to 

these two monthsand do not provide much utility for estimating larval distributions. Limited data 

suggest that most spawning occurs near the Mississippi River plume frontal region with larval 

and juvenile yellowfin tuna present seaward and downstream (southwest) of the plume along 

the 200 m. In the absence of juvenile distributional data, it is likely that their distributions overlap 

with the larvae. 

STUDY PRODUCTS: Benfield, M.C. and R.F. Shaw. 2005. Potential spatial and temporal 

vulnerability of pelagic fish assemblages in the Gulf of Mexico to surface oil spills associated 

with deepwater petroleum development. Prepared by the Department of Oceanography and 

Coastal Sciences, Coastal Fisheries Institute, Louisiana State University. U.S. Dept. of the 

Interior, Minerals Management Service, Gulf of Mexico OCS Region, New Orleans, LA. OCS 

Study MMS 2005-012. Xv+158 pp. 

Companion Microsoft Excel Spreadsheets: Data for each taxon and stage is provided in a 

Microsoft Excel spreadsheet separate worksheets for each taxon and life history state. A series 

of files are provided for each month of the year. There is one set for adults and a second set for 

larvae/juveniles. Within each file there are worksheets for each species containing latitude and 

longitude coordinates and a matrix of cells containing distributional data are encoded with 

values of 2 (confirmed), 1 (reasonable inference), or 0 (unreported). The cells corresponding to 

the study area are colored yellow. Within each monthly Excel spreadsheet for either 

larvae/juveniles or adults there is a worksheet called Distribution Calculator that provides a 

means of querying the data. Individual worksheets for each taxon are accessible via tabs at the 

bottom of the spreadsheet page. The Distribution Calculator worksheet allows the user to enter 

the western and southern coordinates of the location to be queried. The calculator will query 

each taxon for the month in question and return the predicted distribution of adults or 

larvae/juveniles of each taxon at the location of interest. 
ACCESS NUMBER: 30660-19962