In an effort to assess the effects of surface water withdrawl,
FWRI's Fisheries-Independent Monitoring Program, Southwest Florida
Water Management District, and Tampa Bay Water are working together
to monitor several rivers along the west coast.
As Florida's population increases, demands for surface water
withdrawals to meet potable water demands also increase. Freshwater
must often be extracted from various water bodies in the state to
meet this demand, and tidal rivers are often selected as suitable
locations. However, the same freshwater that is being harvested is
a key ingredient for the state's estuaries.
Each day, millions of gallons of freshwater enter into Florida's
bays and estuaries. This water quickly mixes with the saltwater,
creating within the estuary a salinity gradient that ranges from
freshwater to full-strength saltwater. This range between
freshwater and saltwater is necessary for the estuary's inhabitants
to flourish. In fact, the majority of marine fish caught by
recreational anglers (i.e. red drum) depend upon this influx of
freshwater for at least the early stage in their lives.
Several rivers flowing into Florida's estuaries have become
sites for freshwater withdraw to satisfy the demands of Florida's
growing population. Scientists have worked for years to define the
point at which withdraws begin to disrupt the ecosystem. Water
resource managers call this limit the Minimum Flows and Levels
(MFL) for the water body. Florida statutes (Section 373.042)
require that water management districts across the state establish
MFL for all water bodies. Several of the water management districts
have funded short-term monitoring programs to develop baseline data
that can be used to establish more meaningful MFL.
In addition to Minimum Flows and Levels, the water management
districts oversee water resource permitting. In the late 1990s,
Tampa Bay Water, a government agency that provides wholesale water
to Hillsborough, Pasco, and Pinellas counties, was granted a permit
by the Southwest Florida Water Management District to withdraw
additional surface waters from the Hillsborough, Alafia, and Palm
rivers during periods of high water flow. In granting this permit,
the Southwest Florida Water Management District (SWFWMD) required
that Tampa Bay Water initiate the comprehensive Hydro-Biological
Monitoring Program (HBMP). The HBMP is designed to ensure that
water flows do not deviate from the normal rate to the extent that
water quality, vegetation, and animal populations are adversely
affected, that salinity distributions in tidal streams and
estuaries are not significantly altered, and that recreational use
and aesthetic qualities of the resource are not adversely
The multi-disciplined HBMP established by Tampa Bay Water
surveys hydrology, water quality, benthic fauna, zooplankton and
ichthyoplankton, fish and macro-invertebrates, emergent and
shoreline vegetation, and birds. Most of the surveys employ a
stratified-random sampling design, so the data collected can be
used to describe the entire study site. The Fisheries-Independent
Monitoring Program at the Fish and Wildlife Research Institute has
been contracted to conduct the fish and macro-invertebrate survey
portion of the study.
During each of these studies, the Fisheries-Independent
Monitoring (FIM) program collects fish and macro-invertebrate
samples at randomly selected sites within each river. In each study
area, shallow water samples (<1.8 m) are collected with 21.3 m
seines, and deeper water samples (>1.8 m) are collected with 6.1
m otter trawls. All fish and select macro-invertebrates (blue
crabs, stone crabs, pink shrimp, and grass shrimp) are identified
to species and counted.
Fish lengths are also recorded prior to releasing the animals.
Specimens are visually inspected for external abnormalities, such
as parasites, ulcers, and tumors. Animals determined to have
abnormalities are returned to the lab for further analysis.
Additional data recorded at each sample site include the
- Habitat-bottom vegetation, bottom type, and shore type
- Site-latitude, longitude, and depth
- Weather-wind, cloud cover
- Water-salinity, temperature, pH, dissolved oxygen, clarity,
Also, monitoring is taking place on the Myakka river and Venice
inlet for 18 months to support establishing MFL. A similar
twelve-month study is taking place on the Weeki Wachee river.