Assessing Fisheries and Aquatic Resources in the Mobile-Tensaw Delta

Alabama’s Mobile-Tensaw Delta is a unique ecosystem where freshwater and marine environments meet.  The aquatic resources found throughout the Delta represent an important, yet relatively unexplored treasure along Alabama’s Gulf coast.  Recreational angling in this area, particularly for largemouth bass, has seen significant increase over the last several years with numerous local, regional, and national tournaments.  While we know quite a bit about largemouth bass in ponds, lakes, and reservoirs, much less work has been conducted in coastal and estuarine areas, like Alabama’s Mobile-Tensaw Delta.  In addition, the largemouth bass population there may be genetically distinct from fish upstream in the Alabama River.   Given this, Auburn scientists have focused research efforts on the largemouth bass, and broader aquatic resources of the Mobile-Tensaw Delta.


In the Mobile-Tensaw Delta, Auburn scientists are:

Quantifying largemouth bass population growth and mortality, and how these parameters change over time and space (especially across the salinity gradient).
Evaluating factors thought to be important in affecting recruitment of age-0 largemouth bass in the Mobile Delta.
Assessing movement patterns of both largemouth bass and southern flounder.
Quantifying mercury accumulation in largemouth bass and southern flounder.
Quantifying reproduction by and recruitment of sunfishes.
Working with local angling clubs to provide them with information and to collect tag returns from their fishing.


Scientists in the Department of Fisheries and Allied Aquacultures are currently studying the aquatic resources throughout the Mobile-Tensaw Delta near Mobile, including in particular the largemouth bass population.  Sampling includes collection of juvenile and adult largemouth bass from near I-65 to the north to below the US-80/98 causeway near I-10 to the south. Samples are taken approximately once per month and cover a wide range of salt concentrations, vegetation abundance, and water temperatures, creating a far more complete picture of this important species in this unique aquatic system.
In addition to this regular sampling, scientists are also tagging fish with both visible external tags, and internal sonic tags to explore largemouth bass movement patterns, particularly as related to changes in the salt concentration gradient throughout the Delta. Through this combination of field research and work in the laboratory, a complete data set is being generated for this important system.


Information gathered through this project has confirmed that these fish are different from the freshwaters of Alabama.  For example, the delta largemouth bass is shorter and stouter than its landlocked cousins. In addition, the connection to the Gulf gives largemouth bass the opportunity to feed on marine organisms that routinely migrate into the delta. One of the most common foods for these delta bass is the blue crab!  In addition, reproduction by sunfishes appears to be different from in freshwater systems, as their larvae are not collected in the open waters as has been found in inland systems.

Historically there has been a great deal of human influence on this population through habitat modification. Discussions are under way concerning the modification of the Causeway to restore the Mobile Delta to its natural setting. Work by scientists in the Fisheries and Aquaculture Peaks of Excellence program is providing a strong baseline data set that can be used to predict affects of Causeway modifications and to compare similarly collected data after any such modifications.