Assessing Fish and Shellfish Populations
A fish (or shellfish) population assessment, or stock assessment, is an estimation of the amount of fish or shellfish that are available in the population and the rate they are removed by fishing. Managers use stock assessments to determine if a population is undergoing overfishing or if it is overfished. If overfishing is occurring or if the population is overfished, managers recommend or implement measures to bring fishing rates and/or the population back to stable levels.
To develop a stock assessment, we need three types of information:
- A measure of abundance (how many fish or shellfish are available for capture), obtained through our fish sampling efforts.
- Information on how many fish have been removed from the population by the fishery. Information on recreational fishing comes from dockside creel surveys such as LA Creel; information on commercial fishing comes from our trip ticket program.
- Life history information on the species—e.g. how fast it grows, how often it reproduces, if it migrates, and its natural life span. This information is primarily acquired from analyses conducted on the fish we sample.
We plug all of this information into stock assessment models, which estimate the impact of fishing on a specific fish or shellfish population. Managers use these assessments to recommend management measures such as seasons and limits to the Louisiana Wildlife and Fisheries Commission for implementation.
LDWF conducts stock assessments for a number of fresh and saltwater species. We focus on black bass and crappie populations during three-year studies on different freshwater bodies around the state. The Louisiana Legislature mandates that we assess southern flounder, black drum, and sheepshead every five years and striped mullet every year. We assess oysters every year and other important commercial and recreational species such as blue crab, spotted seatrout, and red drum every three years or as needed for proper management.
Overfishing means fishing rates are too high. Overfished means that there are not enough individuals in the population.