The Fisheries-Independent Monitoring program (FIM) conducts
stratified-random sampling to estimate fish abundance and
population trends in seven regions around Florida.
The management of Florida's marine and estuarine fisheries
resources requires the collection of a variety of information on
many species. To help provide that information, the
Fisheries-Independent Monitoring (FIM) program established a survey
project using stratified-random sampling (SRS), a technique used to
describe and compare population trends. FIM initiated
stratified-random sampling in 1988 with a survey of Tampa Bay.
Surveys are underway in seven regions: Apalachicola Bay, Cedar Key,
Charlotte Harbor, Florida Keys National Marine Sanctuary, Indian
River, Northeast Florida, and Tampa Bay. From 1992 to 1996, FIM
also used this method to survey the Choctawhatchee Bay region of
Stratified-random sampling, an approach designed to reduce
statistical error, is a tool for managing the habitat variations
that complicate data collection. Using SRS, FIM divides each
selected survey region into zones based on logistical and
hydrological characteristics. Each zone is then stratified, or
assigned, into areas by habitat (for example; depth, seagrass beds,
shore type, etc). FIM conducts monthly sampling at sites randomly
selected from the strata available for each zone.
To ensure the sampling of a wide range of fish sizes and ages
during an SRS survey, FIM uses a variety of techniques and fishing
gear to collect fish population data . Smaller fishes are usually
collected with a 21-meter seine or a 6.1-meter otter trawl. FIM
uses the 21-meter seine in water depths of 1.8 meters or less; they
use the trawl in water of greater depths. Larger subadult and adult
fishes are collected using 183-meter haul and purse seines. Program
biologists use a haul seine along shoreline habitats and a purse
seine for open bay sampling. FIM also employs visual surveys,
during which divers count, identify, and estimate the sizes of
fishes observed, to collect data in the Florida Keys National
Fisheries-Independent Monitoring program scientists try to
describe every possible variable for the sampled regions. Fish data
collected include species, size, sex, and numbers of fish caught.
For each site, FIM records habitat features such as the type and
quantity of submerged and shoreline vegetation and the presence of
seawalls or oyster beds. Measurements of water quality include
temperature, pH, salinity, and dissolved oxygen. Scientists examine
the fish collected at each sample site for any external
abnormalities or signs of poor health. Tissue samples are taken
from selected fish for analysis of mercury content.
Resource managers use the data from these surveys in many
important ways. In addition to providing estimates of the relative
abundance of many economically and recreationally important
species, the data allow the development of annual abundance models
of juvenile fishes. These models may be used to predict the
availability of a species in the near future.
Often, the information is also useful in maintaining and
creating recreational fishing regulations. Size restrictions for
various fish species are largely determined by SRS data, which
describe the size and age structure of populations. Finally,
surveys provide information about fish distributions and habitat
use to the Inshore-Marine Monitoring and Assessment Program (IMAP),
a multi-agency project characterizing the ecology of inshore waters
in Florida and several other states.
Sound management is required to preserve the health of Florida's
marine environment for our present and future enjoyment. Using SRS,
the Fisheries-Independent Monitoring program provides the numbers
and information needed to determine necessary fisheries management
measures and to assess the effectiveness of those measures after
they are enacted.