FORECAST FOR THE 2004 BROWN SHRIMP SEASON IN THE WESTERN GULF OF MEXICO, FROM THE MISSISSIPPI RIVER TO THE U.S. - MEXICO BORDER

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

June 21, 2004

To All Concerned:

FORECAST FOR THE 2004 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 2004 – June 2005).   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.

The 2004 abundance indices are varied relative to offshore brown shrimp production estimates.  The Galveston Bay bait index forecasts a below average year at 22.5 million pounds from offshore Texas waters from July 2004 through June 2005.   The 2004 Louisiana indices point to an above average yield of approximately 41.2 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 63.7 million pounds during the 2004-2005 season.  This is above the 1960-2002 historical average of 56.5 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.  This year, air temperatures in late winter and early spring were mild, with the exception of two weather fronts in mid-February and mid-April.  Each of these fronts lasted approximately a week and brought record low temperatures and low tidal water in coastal areas of the western Gulf of Mexico.  Rainfall in April through early June has been well above normal for coastal areas of Texas and western Louisiana (Table 1) and has resulted in very low salinities, most notably in May (Table 2).  These lower salinities may have reduced available nursery habitat and slowed or inhibited growth, as evident from the below-average shrimp size observed during the reporting period.

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.  Although temperature and rainfall values were below average (Table 3), our Environmental Model suggests slightly above average production off Texas this season when bay water height (April-May) is incorporated into the model. 

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 2004 were obtained from NOAA Fisheries port agents.  Catch rates recorded during the reporting period may not adequately portray catch-per-unit effort due to very low shrimping effort.   Small shrimp size, low dockside prices and high fuel costs contributed to the decrease in effort.   Based on the data available, all Texas bays with the exception of Matagorda Bay experienced below average catch rates as compared to the 1986-2003 historical average (Table 4).  No landings were reported in San Antonio; heavy rains and the release of water from an upstream dam were cited as reasons.  Similarly, Aransas Bay had very limited effort.  Very small shrimp (i.e., 100+ count per pound) dominated the catch in most Texas bays.   The dominant size categories in Matagorda Bay were 71-80 and 81-100 count shrimp.

Baxter Bait Index

Consistently, for the past 44 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 began the last week of April.  Highest catch-per-unit-effort occurred the first week of June.  Very low salinities prevailed throughout most of May and may have reduced available nursery area required for optimal shrimp growth and survival.    Using the period from 1981 through 2003 in the bait versus offshore landings regression model, a value of 22.5 million pounds is the estimate of production from Texas offshore waters. This value is 3.9 million pounds below the average catch of 26.4 million pounds for the 1960 - 2002 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 2004 May catch data (13.67 million pounds) in our Louisiana model, we predict a harvest of 41.2 million pounds for Louisiana west of the Mississippi River for the 2004-2005 season.  This is well above the historical average of 30.1 million pounds.  Louisiana Department of Wildlife and Fisheries scientists estimated that 0.74 million acres of marsh with salinities greater than 10 ppt were available this year for brown shrimp, a decrease of approximately 0.61 million acres as compared to this time last year, and the lowest acreage recorded since 1980.

Forecast Summary

Based on 2004 brown shrimp abundance indices, brown shrimp production off Texas will be below average for the July 2004-June 2005 season.  Louisiana production, on the other hand, will be well above average for the May 2004 through April 2005 season.   If you would like more information regarding this forecast, or for other marine fishery information, please contact us at 409-766-3500.

Sincerely,

Roger Zimmerman, Ph.D.
Laboratory Director