Weeki Wachee River System Recommended Minimum Flows and ...

5.2 Fish
5.2.1 Descriptive (Adapted from Matheson et al. 2005)
Fish and invertebrate usage of Weeki Wachee was investigated at the juvenile and
nekton life stages using three sampling protocols which capture differing size and
habitat usage within the river. The general objective was to develop a database of use
and relate the number of organisms (abundance) and location of capture to variations in
freshwater inflows. The tidal Weeki Wachee, Mud River and nearshore Gulf of Mexico
were divided into four zones (Table 5-3) from which twenty monthly plankton net tows,
seine and trawl samples were collected along with ambient measurements of
temperature, salinity, pH and dissolved oxygen.
Table 5-3
Fish / Invertebrate Sampling Zones
Zone
Zone 1 – Gulf
Zone 2 – Lower Weeki Wachee
Zone 3 – Mud River
Zone 4 – Upper Weeki Wachee
Zone Limits
-1.5 to 0.5 km
+0.0 to 1.5 km
+1.5 to 3.8 km
+1.5 to 3.8 km
The fish / invertebrate usage of the Weeki Wachee differs in several ways from other
southwest Florida tidal rivers sampled using similar sampling techniques. The system is
short by comparison, and the estuarine portion is very compressed, generally extending
less than two kilometers from the Gulf. The Gulf and the mouth of the submerged tidal
portion is heavily vegetated (See section 3.2). Furthermore, the geographic location is
at the northernmost extent of mangrove, and the dominant shoreline habitat is emergent
marsh. Thus, the physical habitat present is quite different from systems to the south.
Finally, the system is spring-fed at relatively high discharge velocities and has a very
small watershed resulting in high visibility conditions and coarse substrate.
The use of three types of gear targets both different size organisms and use of different
portions of the available habitat. Seine nets (3.2 mm) were used to sample the shallow
areas, while a vessel-towed trawl (3.2 mm) was used to sample the deeper confines of
the main channel. Typical sampling area for the seine was approximately 68 m 2 , while
a typical trawl swept an area of about 720 m 2 . Seine and trawl sampling was conducted
during the day. Seines and trawls were used to survey larger organisms that evade the
plankton net. The dominant catch from both seines and trawls is juvenile fish and adults
of smaller fish. Larger macroinvertebrates (namely pink shrimp and blue crab) are also
regularly captured in seine pulls and trawl tows.
A plankton net (0.5 mm) was also towed behind a vessel in such a manner as to sample
from near bottom to surface. A flow meter mounted ahead of the opening cone
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Proposed Minimum Flows and Levels for Weeki Wachee River Page 74 of 164
Biological Characteristics