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Fisheries-Independent Monitoring Using Stratified-Random Sampling

The Fisheries-Independent Monitoring program (FIM) conducts stratified-random sampling to estimate fish abundance and population trends in seven estuarine regions around Florida.

The effective and timely management of Florida's marine and estuarine fisheries resources requires the collection of a variety of information on many species. To provide information on trends in populations, the Fisheries-Independent Monitoring (FIM) program was established to survey fishery resources in Florida estuaries. The FIM program initiated sampling in 1989 in the Tampa Bay and Charlotte Harbor estuaries. Sampling surveys are currently conducted in seven estuarine regions of the state: Apalachicola Bay, Cedar Key, Tampa Bay, Sarasota Bay, Charlotte Harbor, Indian River Lagoon, and Northeast Florida.

The FIM program uses a stratified-random sampling (SRS) design, an approach which distributes sampling effort among habitat types and directs greater sampling effort into habitats with higher variability in catches in an effort to reduce variability in the data. With the SRS design, FIM divides each estuary to be surveyed into zones based on hydrological and logistical characteristics. The different habitat types (for example: depth, seagrass beds, shore type) available within each zone are then identified as strata. The FIM program conducts monthly sampling at sites randomly selected from the strata available within each zone.

seine net

A variety of techniques and sampling gears are used by the FIM program to ensure that the wide range of species, sizes, and ages necessary for stock management are sampled during each monthly survey. Smaller fishes are collected with both a 21.3-meter seine and a 6.1-meter otter trawl. The FIM program uses the 21.3-meter seine in water depths of 1.8 meters or less, while the trawl typically samples water depths of 1.8 or greater. Larger sub-adult and adult fishes are collected using 183-meter haul seines in water depth of 3.0 meters or less. The two seine types sample shoreline habitats and open bay areas with both seagrass and non-vegetated bottom habitats. The trawl is typically deployed in deeper, open water habitats but is also deployed over deeper seagrass habitats.

With each gear deployment, FIM program scientists record data that describe the physical features, such as water quality and habitat types, of the sampling site and the fish community collected. Recorded physical features include measurements of the type and quantity of submerged (seagrasses, bottom type, oysters, etc.) and shoreline (mangroves, seawalls, emergent vegetation, etc.) habitats at each sampling site. Measured water quality parameters include temperature, pH, salinity, and dissolved oxygen. All species of fish, shrimp and crabs collected in each gear deployment are identified and counted and a representative subsample are measured. Fish greater than 75 mm are examined for external abnormalities (tumors, ulcers, parasites, etc.) and abnormal specimens are returned to FWRI’s aquatic heath scientists for further analysis. Tissue samples for mercury concentration, ageing, reproductive condition, diet, and genetic studies are taken from selected fish and analyzed by scientists, both within and external to FWRI.

Analyses of the FIM program data are used by resource managers to assess abundance trends for resource species, define essential fish habitat, and describe life-history parameters such as age, growth and age of maturity. Since the FIM program gears and sampling techniques tend to target juvenile and sub-adult fishes, the abundance trends are a valuable forecasting tool for future adult stocks. Fisheries managers use these FIM data as well as other fisheries data to assess the overall well-being of fish populations.

The FIM program data are frequently used to assess the impact of environmental perturbations such as red tides, extreme cold events, and oil spills. For instance, a severe cold event in January-February 2010 resulted in a large fish kill of snook, a very cold sensitive species, in Florida estuaries. In 2010, the FIM program data indicated that abundance of snook was lower than any year since sampling started (1996).  This information led to an emergency closure on the harvesting of snook until they recovered.


Management measures, such as the one-fish-per-person, per-day bag limit, and annual closed seasons protect snook during vulnerable times such as cold weather and spawning. Other measures, including minimum and maximum size limits protect juvenile and older breeding fish within the population.  These management measures contribute to rebuilding and protecting snook populations on both coasts. Snook numbers currently meet or exceed FWC management goals and a limited harvest season for snook is allowed. Visit the snook regulations Web page for specific East coast and West coast seasonal closures and maximum and minimum size limits.


Another example of an environmental perturbation being studied in the FIM program data is the prolonged red tide event of 2005.  Although not resulting in immediate management actions, the red tide event is evident in the FIM program abundance trends for several economically important species (pink shrimp, red drum, and spotted seatrout) in Tampa Bay. Data analyses such as this provide valuable tools for making informed and timely management decisions.

Sound management is required to preserve the health of Florida's marine environments for our present and future enjoyment. The FIM program’s stratified-random sampling design and extensive fisheries surveys provide abundance estimates and population parameters needed to determine stock sizes.  These data and analyses are vital for determining appropriate fisheries management measures and to assess the effectiveness of those measures after they are enacted.