Use of Long-term Monitoring Data for Fishes and Macroinvertebrates in the
Development of Performance Measures for the Modified Water-Delivery Project
Joel C. Trexler
Florida International University, Miami, FL
Frank Jordan
Loyola University New Orleans, LA
Carl Ruetz
Grand Valley State University, Muskegon, MI
John Chick
Illinois Natural History Survey, Champaign, IL
William F. Loftus
U.S. Geological Survey, Miami, FL
Sue Perry
Everglades National Park, Homestead, FL
The Modified Waters Delivery Project (MOD Waters) is an on-going effort to
improve hydrological management of the Everglades National Park (ENP).
Starting in 1996, we initiated a monitoring program to assess the impacts of Test
7, an iteration of that effort, on ENP aquatic fauna. Our efforts focus on fishes
and large invertebrates that can be sampled by 1-m2 throw trap, as well as large
fishes that could be sampled by airboat-mounted electrofisher. Seventeen longterm study sites were added to an existing set of three study sites in northern
Shark River Slough to permit the establishment of a long-term database for use
both to assess management impacts and serve as reference sites and to establish
baseline ecosystem conditions. Eleven study sites are in WCA-3A and 3B, 6 are
in Shark River Slough, and 3 are in Taylor Slough, reflecting the relatively
different spatial areas of these regions. The sites encompass a range of
hydroperiods and nutrient conditions. At this point, we have 6 complete years of
information, with throw-trap samples collected in February, April, July, October,
and December at all or most sites in each year. Systematic electrofishing was
initiated in 1997 at a subset of the throw-trap sites, and is conducted in February,
April, July, and October.
We have used these data to develop performance measures for assessing MOD
Waters and Comprehensive Everglades Restoration Plan (CERP) activities. A
key result is that fish and macroinvertebrate community composition is sensitive
to the time since their local site was dried. For example, the density of bluefin
killifish (Lucania goodei) and least killifish (Heterandria formosa) are diminished
for as long as four years following a drying event. Eastern mosquitofish
(Gambusia holbrooki) repopulate sites very rapidly following drying events, and
are not good indicators of dry-down events. Recent water-management actions
under the Interim Sparrow Operating Procedure (ISOP), have affected the rate and
frequency of drying in the southern portion of the Everglades. Our monitoring
data, coupled with statistical modeling, indicate that this operation may have
affected the abundance of small fishes in some areas of ENP by altering the
drying pattern and the area of drying. A recent series of dry years, possibly
coupled with such water-management actions, have produced a marked affect on
large fishes that we monitor by electrofishing. The invertivorous lake chubsucker
(Erimyzon sucetta) was a dominant fish in the 8-cm and greater size classes in
1997 through 1999 in both Taylor and Shark River sloughs. However, its
abundance has been dramatically lower since the dry season of 2000, and only
one specimen was collected in Taylor Slough since that time. Dry-down events
also appear to have altered the size distribution of lake chubsucker in Water
Conservation Area 3A. Similar declines in the number and size of large-bodied
fishes have been reported following other Everglades drying events in the 1980s
and 1990s. Therefore, the relative abundance and size structure of lake
chubsucker and the piscivorous gar (Lepisosteus platyrhincus) and largemouth
bass (Micropterus salmoides) show promise as performance measures for
hydrological management.
Joel, Trexler, Department of Biological Sciences, Florida International University,
Miami, FL 33199, Phone 305-348-1966, Fax 305-348-1986, trexlerj@fiu.edu,
Ecology and Ecological Modeling