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(29,940 interviews) is reported by Ault et al. (2001). One-hundred forty three of
the 325 species of fish and invertebrates documented in that study were part of
the recreational fishery. Again the dominant single species was an invertebrate,
the spiny lobster (Panulirus argus), followed by grunts and snappers. The “highly
prized gamefishes, such as bonefish, tarpon and snook” were hardly present in
any of the samples. Even spotted seatrout, identified by Alleman et al. (1995) one
of the top five fish species harvested in the Bay based upon data reported in
1984, was only a minor component of the creels sampled (565 fish in 30,000
interviews). Apparent harvest of this species by numbers and CPUE (catch per
unit effort) peaked in the early 1980’s and has declined since. The 983 randomly
located night time trawls (1996-2000) in BNP targeting pink shrimp yielded just
53 spotted seatrout (Ault et al. 2001).
Certainly sampling bias, both in which areas of BNP fisherman choose to fish in
and for what species, and the lack of larger seine samples in inshore waters,
skewed the samples to capture or document harvest of the “highly prized
gamefishes” above, but not likely the presence of spotted seatrout, which should
have shown up in nighttime shrimp trawls.
Similarly, a 14 month study with 224 samples, spotted seatrout comprised less
than 0.02% of the total catch (Serafy et al. 1997). Ninety-six percent (96%) of all
Valued Ecosystem Components
Freshwater Flow and Ecological Relationships in Biscayne Bay 4-40
trout were captured north of Rickenbacker Causeway, and 68% came from just
one of the eight sampled areas, the most northerly station at the mouth of the
Biscayne Canal. Clearly spotted seatrout are not a common species in the
sampling efforts described, or in the recreational creel. It can only be
hypothesized that some as-yet-unidentified habitat factor is not appropriate, a
particular food source is not available, or that the very intense shrimp trawling in
what is identified by Ault et al. (1999) as the highest quality habitat for juvenile
spotted seatrout (west side of Central and South-central Biscayne Bay) may be
eliminating juvenile spotted seatrout as bycatch. Although Bortone (2003) has
characterized spotted seatrout as a potentially ideal indicator species for
monitoring estuaries, it does not appear it is a good indicator within Biscayne
Bay for establishing MFL's.
Although sampling within mangrove lined tidal creeks has occurred in other
portions of Florida (Lewis et al. 1985, Edwards 1991, Ley and McIvor 2002,
Flannery et al. 2002), no known sampling of this type is known for Biscayne Bay.
Serafy et al. (2003) visually sampled transects in mangrove prop root habitat in
surveys parallel to the shore, similar to Ley and McIvor (2002) and found a
similar group of fishes dominant. Part of the problem is likely the lack of any
“natural” mangrove lined tidal creek, since most have been channelized, or
denied historical levels of freshwater flow (Meeder et al 1999, 2001, 2002).
Although there is much discussion about the potential nursery habitat role of
mangroves, tidal marshes and tidal creeks within them, specific data is often
lacking (Sheridan and Hays 2003). This is more likely a problem of sampling
rather than any factual basis to reject the potential hypothesized role of coastal
wetlands as nursery habitat for fish and decapods.
In summary, while there is an abundant fish community in Biscayne Bay, past
modifications to freshwater flow have likely eliminated most if not all of the
historical mangrove or tidal marsh lined tidal creeks with any kind of “natural”
tidal and freshwater drainage hydrology. Thus use of these systems, and any
potentially associated species as a biological indicator for freshwater inflow
management, would be fraught with speculative outcomes, rather than
predictable outcomes.
This is further supported by the work on Faunce et al. (2002) where visual
sampling for gray snapper in an area protected from fishing, was compared to an
area open to fishing. Differences in the size structure of the two observed
populations were significant, with those observed in the closed area being two
size classes larger. The fishery for gray snapper is characterized as “growthoverfished” in both this paper and in Ault et al. (1998). With the confounding
error introduced by overexploitation, and the inherent difficulty in quantitatively
sampling for fish, use of any fish species or community as an indicator for
Valued Ecosystem Components
Freshwater Flow and Ecological Relationships in Biscayne Bay 4-41
freshwater management in Biscayne Bay seems unwarranted until much more
data is available about nearshore and tidal creek fish populations, and perhaps
better management of these fisheries is introduced.
Seagrass
Fourqurean et al. (2003) have recently published the results of water quality
sampling and seagrass occurrence by species and cover for 677 stations in Florida
Bay sampled between March 1991 and March 2000. The sampling and
correlations derived from the data were intended to attempt to construct "habitat
requirements" models for the five species of seagrass encountered: turtle grass,
manatee grass, shoal grass, paddle grass and wigeon grass. No stargrass was
observed in the sampling, and Johnson's seagrass has never been observed south
of Key Biscayne in Biscayne Bay, and therefore is not known to occur in Florida
Bay. Eight seagrass community types, including no seagrass, were identified, and
characterized as to the various sampled parameters.
For salinity, the results can be summarized as: "Ruppia-Halodule communities had
the lowest and most variable salinity...while yearly mean salinity in the H.
decipiens, Syringodium filiforme, and dense mixed-species beds was relatively high,
with low variability. Intermediate yearly mean salinities and relatively high
annual variability were found in the Halodule wrightii, dense Thalassia, and sparse
Thalassia communities."
Thus all the seagrasses, and mixed seagrass communities exhibited some
apparent habitat requirements for specific mean salinities, and could tolerate
various ranges of variation. From the perspective of MFLs, the goal to manage
shoal grass and overlying salinities to maximize production of shrimp in a
polyhaline zone (18-30 psu) along the west shore of Central and South-Central
Biscayne Bay would appear to be best accomplished by lowering mean annual
salinity and increasing variability in salinity to reestablish a range of salinities to
support a Ruppia-Halodule gradient into deeper water where Thalassia would
likely predominate.
SALINITY TOLERANCES, PREFERRED HABITATS AND LIFE CYCLES OF
POTENTIAL INDICATOR SPECIES OR SUITES OF SPECIES
As stated by Sklar and Browder (1998) "Although estuarine organisms are
generally euryhaline, few occur throughout the entire range of salinities from full
seawater strength to brackish. Rather, several communities of organisms occur
within an estuary, each more abundantly within a relatively narrow part of the
salinity spectra...As a result, shifts in isohalines cause major changes in
community structure...Such shifts reduce or eliminate suitable living habitat by
Valued Ecosystem Components