Fisheries-independent monitoring is a system-wide approach and evaluates marine communities and the populations of fish and invertebrate species that comprise them. Fisheries-independent monitoring also investigates habitat conditions for purposes of learning more about system-wide trends.
You may want to compare and contrast fisheries-independent monitoring with fisheries-dependent monitoring (see Fisheries-Dependent Monitoring Learn More), for an understanding of why these studies are performed how data gathered by one program, compliments data gathered by the other.
Scientists use statistically valid sampling to collect fisheries-independent data to supplement fisheries-dependent information obtained from anglers and commercial fishing operations. These monitoring efforts differ from one another. Fisheries-independent monitoring is a system-wide approach and evaluates numerous species along with their habitat conditions. Fisheries-dependent monitoring, on the other hand, monitors the harvest of individual species as they are taken through commercial and recreational fishing.
Regions are divided into hydrological zones, then stratified (or assigned) into areas by habitat type (i.e.; seagrass, mangrove, depth, shore type, etc.). Monthly sampling is then conducted at sites randomly selected from the strata in each zone to monitor juvenile and adult stocks.
A variety of fishing gear and techniques ensure sampling of fisheries in a wide range of sizes and ages. Smaller seines and otter trawls are used to capture smaller fishes, while larger sub-adults and adult fishes are collected using 183-meter haul and purse seines. The State also employs visual surveys, using divers, for data collection in the Florida Keys Marine Sanctuary.
Data collected includes species, size, sex, and number of individuals per species caught. As part of these monitoring efforts, fish are examined for external lesions or abnormalities, and tissue samples are taken from selected fishes for analysis of mercury content. Biologists also record habitat features such as the type and quantity of submerged and shoreline vegetation and the presence of seawalls or oyster beds. Water quality data (including temperature, pH, salinity and dissolved oxygen) are also collected.
Resource managers use the data to track the relative abundance of fish stocks and to forecast trends. Information and data are also used to support fisheries management and regulation, such as establishing catch-size restrictions, and to gauge the health of marine ecosystems. Juvenile fish indices measure the relative abundance of newly recruiting or young-of-the-year. When combined with data on adult fish, a more comprehensive picture of the condition of a fishery emerges.
Relative abundance is calculated as the median annual number of fish per haul. The process is repeated 500 times for each year to create a robust and representative sampling distribution Summary statistics (10, 25, 75, and 90 percentiles) are then calculated.
Actual numbers and estimates of fishery populations are not calculated or reported in fisheries-independent monitoring, which evaluates only trends in relative abundance.