June 28, 2011


To All Concerned:

FORECAST FOR THE 2011 BROWN SHRIMP SEASON IN THE WESTERN GULF OF MEXICO, FROM THE MISSISSIPPI RIVER TO THE U.S. - MEXICO BORDER.

Prediction Summary

Scientists at the National Marine Fisheries Service (NOAA Fisheries) Southeast Fisheries Science Center's Galveston Laboratory have prepared the following information on prospects for the 2011 brown shrimp season (July 2011 – June 2012) in the western Gulf of Mexico. Data obtained from NOAA Fisheries Galveston Laboratory, NOAA 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 by monitoring the inshore commercial shrimp fisheries in Texas and the inshore and nearshore fisheries in Louisiana. In addition, environmental variables are measured to assess the favorability of conditions in habitat for growth and survival of young shrimp. Collectively, these indices provide an estimate of inshore stock strength prior to shrimp movement into the offshore fishery.

The 2011 abundance indices are varied relative to offshore brown shrimp production estimates. The Galveston Bay bait index forecasts a below average year at 22.2 million pounds from offshore Texas waters; however, increasing catch rates in mid-June (the end of our monitoring surveys) indicate continued strong recruitment not reflected in our model. The 2011 Environmental Model showed favorable conditions in the bay system and predicts above average production for Texas offshore waters. Louisiana indices point to a slightly above average brown shrimp yield 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 53.4 million pounds during the 2011-2012 season. This is slightly below the 1960-2009 historical average of 56.7 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 affect the fate of young shrimp entering the estuaries. Three environmental variables, temperature, salinity and tidal height, have been correlated with subsequent shrimp production. Optimal shrimp growth has been documented in waters greater than 68° F.



This year, above average air temperatures and record low rainfall in late winter and early spring were recorded in coastal areas for both Texas and western Louisiana (Tables 1). Higher salinities (Table 2) and strong southerly winds that sustained tidal height levels (Table 3) were recorded during the peak recruitment period for brown shrimp. These three environmental factors, temperature, salinity and tidal height, increased available nursery area thus allowing for greater distribution of juvenile brown shrimp entering estuaries.

Galveston Bay Production/Baxter Bait Index

The Galveston Bay Bait Index, consistently our most reliable estimate of subsequent brown shrimp production off the Texas coast for the past 51 years, is derived 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 observed at the onset of our monitoring period. Based on length frequency data, three growth waves of brown shrimp were documented. Strong recruitment continues to be observed with catch rates greater than 44 pounds per hour. This is expected to continue through the month of June. Unlike previous years, white shrimp have been present in the bay system throughout the season. High salinities and tides increased available nursery habitat allowing for a wider distribution of young brown shrimp. Using the period from 1981 through 2009 in the bait versus offshore landings modified regression model using a seven-week sampling season, a value of 22.2 million pounds of brown shrimp is forecast for 2011-2012 catch in Texas offshore waters. This value is 3.8 million pounds below the average catch of 26.0 million pounds for the 1960 - 2009 period.

Catch per Unit Effort (CPUE) in the Inshore Texas Fishery

Texas bay commercial brown shrimp catch rates and size composition data for May 2011 were obtained from NOAA Fisheries port agents. All Texas Bays experienced catch rates below the 1986-2010 historical average (Table 4). The May brown shrimp size composition in Matagorda and Galveston Bays was dominated by small shrimp (100+; 81-100 count/pound). Corpus Christi and Aransas Bays catches were primarily 71-100 count/pound shrimp, with San Antonio Bay comprised of 51-60 count/pound shrimp.

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. The heaviest contributing factor, temperature during mid-April, was above average this year (75.6ºF). Drought conditions have been prevalent in Texas for several months; however, due to a single significant rainfall event on March 5, 2011, rainfall in March was higher than average (2.55”). Relatively high tidal heights during late April and early May were recorded at approximately 5.61 feet. Using these environmental parameters in our model suggest above average production of brown shrimp from Texas as related to environmental conditions conducive for optimal shrimp growth and survival.


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 2011 brown shrimp catch data (8.5 million pounds) in our Louisiana Model, we predict a harvest of 31.2 million pounds for Louisiana west of the Mississippi River for the 2011-2012 season. This is above the historical average of 30.7 million pounds. Environmental variables in Louisiana during April including temperature and rainfall suggested favorable conditions for above average production. Mississippi River discharge was approximately 845 thousand cubic feet per second in April, and similar to that of years above average production. However, historic Mississippi River flows during May evidenced by record flood stages reported at all monitoring stations along the Mississippi and Atchafalaya Rivers could potentially affect (e.g., by contributing to hypoxia) brown shrimp catch this year.

Summary

The 2011 indices of juvenile shrimp abundance and catch are mixed. We predict a slightly below average harvest for the western Gulf of Mexico during the July 2011 - June 2012 season. However, environmental factors (notably salinity, tidal height in marshes and temperature) are favorable for continued recruitment and stock growth. 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/>.



Sincerely,



Roger Zimmerman, Ph.D.
Laboratory Director