June 24, 2009


To All Concerned:

FORECAST FOR THE 2009 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 2009 – June 2010). Data obtained from NOAA Fisheries Galveston Laboratory Fishery Management Branch, 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 assessed to quantify the amount and type of habitat required for growth and survival of young shrimp. Collectively, these indices provide the estimate of stock strength prior to movement into the offshore fishery.

The Galveston Bay Bait Index forecasts a harvest of 24.7 million pounds from production in offshore Texas waters from July 2009 through June 2010. This is approximately 1.3 million pounds below the 1960-2007 historical average. However, the 2009 Environmental Model showed favorable conditions in the bay system and predicts above average production for Texas offshore waters. Louisiana indices point to slightly below average brown shrimp yield this season from west of the Mississippi River to the Texas-Louisiana border. Input variables used in Louisiana Model are dependent on May catch production from Louisiana. Similar to last year, and due to economic and post-hurricane related factors, many vessels in Louisiana and Texas remained at the dock. Thus commercial fishery data used in current prediction models may not accurately reflect overall shrimp abundance due to reduced effort and catch. Nevertheless, we choose to use the Louisiana Model as our best estimate of production. Yield from Louisiana inshore and nearshore waters is predicted to be approximately 29.2 million pounds. Overall, the western Gulf of Mexico should expect an annual brown shrimp production of approximately 53.9 million pounds during the 2009-2010 season. This is slightly above last year, but below the 1960-2007 historical average of 56.9 million pounds for the two-state area.

During the late winter and early spring of 2009, warm air and water temperatures, high salinities and above average tidal water heights (Tables 1 through 3) in estuarine marsh habitats were favorable for the survival and growth of the subsequent offshore populations. 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. All of these favorable environmental attributes were observed this year. Although predicted values are slightly below the 1960-2007 historical average, environmental factors reflect a strong biological potential.
 

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 largest contributing factor, temperature during mid-April, was near average this year (69.9°F; Table 3). Rainfall during early March was low (Trace = 0.005”). These were offset by relatively high tides during late April and early May (~5.61’). Collectively, the factors 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 (CPUE) in the Inshore Texas Fishery

Texas bay commercial brown shrimp catch rates and size composition data for May 2009 were obtained from NOAA Fisheries port agents. Most Texas Bays experienced above average catch rates with the exception of Galveston Bay, which was below the (1986-2008) historical average (Table 4). The May brown shrimp size composition in Aransas and Galveston Bays was dominated by small shrimp (100+ count). Corpus Christi and Matagorda Bays catches were primarily 61-70 count/pound shrimp, with San Antonio Bay comprised of 61-70 and 51-60 count/pound shrimp.

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 49 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 earlier this year as compared to previous years. Strong recruitment continues to be observed, thus our forecast may be underestimated. High salinities increased available nursery habitat allowing for a wider distribution of young brown shrimp; however, not all traditional shrimp grounds were accessible this year due to the debris from Hurricane Ike. Using the period from 1981 through 2007 in the bait versus offshore landings modified regression model, a value of 24.7 million pounds is forecast for 2009-2010 catch in Texas offshore waters. This value is 1.3 million pounds below the average catch of 26.0 million pounds for the 1960 - 2007 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). Decreased shrimping effort resulting from economic factors may reduce overall production used in our forecast model. Using 2009 May catch data (7.4 million pounds) in our Louisiana Model, we predict a harvest of 29.2 million pounds for Louisiana west of the Mississippi River for the 2009-2010 season. This is below the historical average of 30.9 million pounds. Freshwater discharge data from the Mississippi River were obtained from the Louisiana Department of Wildlife and Fisheries (Table 6). Mississippi River discharge was 767 thousand cubic feet per second in April, lower than recorded in 2008, and similar to that of years above average production.

Summary

The 2009 indices of juvenile shrimp abundance indicate a slightly below average brown shrimp harvest for the western Gulf of Mexico during the July 2009 - June 2010 season. Environmental conditions favor above average shrimp production this year, but the total catch from the shrimp fishery is expected to be slightly below average. 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