Weeki Wachee River System Recommended Minimum Flows and ...

measured volume sampled which was typically on the order of 70-80 m 3 . Plankton
tows were conducted at night. The small organisms collected represent a combination
of zooplankton and hyperbenthos communities. The term zooplankton includes all
weakly swimming animals that suspend in the water column during one, or more life
stages. The distribution of these animals is largely subject to the motion of the waters in
which they live.
In contrast, many of the hyperbenthos are capable of actively positioning themselves at
different locations along the estuarine gradient by selectively occupying opposite tidal
flows. The term refers to animals that are associated with the bottom but tend to
suspend above it, rising into the water column at night.
This faunal mixture of a plankton tow includes the planktonic eggs and larvae of fishes.
Taxa include bay anchovy, sheepshead minnow, killifish and silversides. However, the
numbers of bay anchovy were about an order of magnitude lower than found on other
tidal rivers. Although fish eggs and larvae are the target catch, invertebrate plankton
and hyperbenthos almost always dominate the samples numerically, but these serve as
an important food source for juvenile fish.
Fish and invertebrates can be classified according to their use of estuarine habitat.
Some taxa remain in the estuary year round. This type of usage is termed 'resident'.
Other taxa that utilize the estuarine habitat for only a portion of their life cycle are
considered 'estuarine-dependent'. The utilization may be for spawning, nursery or both.
Table 5-4 indicates usage for taxa which exhibited a statistically significant response to
flow in the Weeki Wachee.
Because of the differences in habitat sampled and capture size, the results of each are
discussed separately. However, at the outset it should be noted that there is an
unavoidable bias in the results as the flow during the sampling period (May 2003-
December 2004) was higher than the mean flow for the prior nine years.
5.2.1.1 Fish Composition
Rainwater killifish were a dominant catch in all three collection devices. Other dominant
plankton net taxon included larval gobies and blennies. Killifish, pinfish and mojarras
accounted for 90 percent of the trawl catch. Seine catch was more diverse with the
following taxa constituting 91 percent of the catch: killifish (2 species), silversides,
mojarras (2 species), pinfish, sheepshead and sailfin molly. Notably absent were sand
seatrout (not collected) and bay anchovy, which was present but in low abundance. The
bay anchovy typically dominates fish assemblages of tidal rivers north and south of
Weeki Wachee, while the seatrout also tends to be very numerous in these rivers.
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Proposed Minimum Flows and Levels for Weeki Wachee River Page 75 of 164
Biological Characteristics