FORECAST FOR THE 2007 BROWN SHRIMP SEASON IN THE WESTERN GULF OF MEXICO, FROM THE MISSISSIPPI RIVER TO THE U.S. - MEXICO BORDER

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Southeast Fisheries Science Center
Galveston Laboratory
4700 Avenue U
Galveston, Texas 77551-5997
409-766-3500 (voice) 409-766-3508 (fax)

June 20, 2007

To All Concerned:

FORECAST FOR THE 2007 BROWN SHRIMP SEASON IN THE WESTERN GULF OF MEXICO, FROM THE MISSISSIPPI RIVER TO THE U.S. - MEXICO BORDER.

Prediction Summary

Each June, scientists at the National Marine Fisheries Service (NOAA Fisheries) Southeast Fisheries Science Center's Galveston Laboratory forecast brown shrimp production from the western Gulf of Mexico for the upcoming year (July 2007 – June 2008). Data obtained from NOAA Fisheries Galveston Laboratory’s Fishery Management and Ecology Branches, NOAA Fisheries port agents, National Climatic Data and Weather Centers, Louisiana Department of Wildlife and Fisheries, Texas Parks and Wildlife Department, and the commercial shrimp industry contribute to this forecast. Juvenile brown shrimp abundance and growth estimates are obtained through monitoring the inshore commercial shrimp fisheries in Texas and the inshore and nearshore fisheries in Louisiana. Environmental variables are further quantified to assess the availability of habitat for growth and survival of young shrimp. Collectively, these indices provide the estimate of inshore stock strength prior to movement into the offshore fishery.

Brown shrimp abundance indices for the 2007 shrimp season suggest above average offshore production for the western Gulf of Mexico. The Galveston Bay bait index forecasts a slightly below average year at 25.9 million pounds from offshore Texas waters from July 2007 through June 2008. The 2007 Louisiana indices point to an above average yield of approximately 32.9 million pounds of brown shrimp this season from west of the Mississippi River to the Texas-Louisiana border. Overall, the western Gulf of Mexico could expect an annual brown shrimp production of approximately 58.8 million pounds during the 2007-2008 season. This is above the 1960-2005 historical average of 56.6 million pounds for the two-state area.

Postlarval brown shrimp begin entering estuaries in Texas and western Louisiana in mid-February and continue through July, depending on environmental conditions. Several waves of postlarve may enter; however, peak recruitment occurs from February through early April. A wide array of environmental and biological parameters affects the fate of young shrimp entering the estuaries. Three environmental variables, temperature, salinity and water height, have been correlated with subsequent shrimp production. Optimal shrimp growth has been documented in waters of greater than 68° F. Favorable nursery area appears to be related to the distribution of high salinity waters as well as tidal water height in interior marshes. Rainfall this year has been above normal (Table 1) and resulted in lower salinities, most notably in May (Table 2). These lower salinities resulted in juvenile shrimp being concentrated in the lower areas of the Galveston Bay system during most of May. During the last week of May, southeast winds and high tides pushed higher salinity waters allowing brown shrimp to move into the upper areas of the bay. Once salinity increased throughout the bay system, catch-per-unit-effort increased slightly, with the highest catch-per-unit-effort occurring the last week of May. Moreover, a second wave of juvenile brown shrimp was observed moving out of the marshes at the end of our reporting period suggesting continued recruitment into the fishery.

Environmental Model

The Environmental Model is used to predict the annual harvest related to the historical production. The model uses Galveston air temperature during mid-April (the key component), rainfall during early March, and bay water height during late April and early May. These components are additive in the model, thus higher values indicate higher catch. Temperature and water height (Table 3) values were above average this year and suggest above average production of brown shrimp from Texas as related to environmental conditions conducive for optimal shrimp growth and survival.

Catch-Per-Unit-Effort in the Inshore Texas Fishery

Texas bay commercial brown shrimp catch rates (heads-on; pounds per hour) and size composition data for May 2007 were obtained from NOAA Fisheries port agents. Catch rates recorded during the reporting period may not adequately portray catch-per-unit effort due to low shrimping effort. Low dockside prices and high fuel costs contributed to the decrease in effort. Based on the data available, San Antonio and Matagorda Bays experienced above average catch rates as compared to the 1986-2005 historical average (Table 4). The catch rate in Galveston Bay was below the historical average. Small shrimp (i.e., 81-100 and 100+ count per pound) dominated the catch in most Texas bays. The dominant size category in Matagorda Bay was 71-80 count shrimp.

Baxter Bait Index

Consistently, for the past 47 years, our most reliable estimate of subsequent brown shrimp production off the Texas coast comes from monitoring the Galveston Bay bait shrimp fishery during late April through mid-June (Baxter Bait Index; Table 5). Recruitment into the commercial bait fishery was approximately two weeks later this year as compared with previous years. Low salinities prevailed throughout most of May and concentrated shrimp in the lower section of Galveston Bay. This limited nursery habitat increased food competition and resulted in suboptimal growth during this time period. Increased salinities and high tides in the latter part of May resulted in a wider distribution of shrimp throughout the bay system, with highest CPUE occurring the last week of May. Moreover, a second wave of young shrimp was observed near the end of our reporting period indicative of continued recruitment into the fishery. Using the period from 1981 through 2006 in the bait versus offshore landings modified regression model, a value of 25.9 million pounds is the estimate of production from Texas offshore waters. This value is 0.1 million pounds below the average catch of 26.0 million pounds for the 1960 - 2005 period.

Louisiana Inshore - Offshore Production

Catch information from Louisiana inshore and offshore fisheries in May is used to estimate total production for the biological year from May through April (Table 6). Using 2007 May catch data (9.7 million pounds) in our Louisiana model, we predict a harvest of 32.9 million pounds for Louisiana west of the Mississippi River for the 2007-2008 season. This is above the historical average of 30.6 million pounds. Louisiana Department of Wildlife and Fisheries scientists estimated that 1.90 million acres of marsh with salinities greater than 10 ppt were available this year for brown shrimp, a decrease of approximately 0.39 million acres as compared to this time last year.

Forecast Summary

Collectively, the 2007 indices of juvenile shrimp abundance indicate an above average brown shrimp harvest for the western Gulf of Mexico during the July 2007 through June 2008 season. If you would like more information regarding this forecast, or for other marine fishery information, please contact us at 409-766-3500, or visit our web site at <http://galveston.ssp.nmfs.gov/galv>.

Sincerely,

Roger Zimmerman, Ph.D.
Laboratory Director