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Influence of Hydrology on Life-History Parameters of Common Freshwater Fishes from S. FL

Project Proposal for 1999

USGS Geologic Division New Proposal - FY 1999


Project title: Influence of Hydrology on Life-History Parameters of Common Freshwater Fishes from Southern Florida
Geographic area: Southern Florida, including Everglades N. P. and Water Conservation Area 3
Project start date: October 1998
Project end date: September 2001

Project chief: William F. Loftus
Region/Division/Team/Section: Eastern region, BRD, FCSC, Restoration Ecology Branch
Email: bill_loftus@nps.gov
Phone: 305-242-7835
Fax: 305-242-7836
Mail address: Everglades National Park Field Office, 40001 State Road 9336, Homestead, FL 33034

Program(s): Integrated Natural Science Program - South Florida Study Area

Program element(s)/task(s): Element 1: Preparation of Information-Synthesis
Task 1.6: Ecological modeling and Success Criteria


Project summary: In the effort to restore the Everglades, fishes have been recognized as good indicators of restoration success. Our long-term fish database was used in the fish simulation model developed to evaluate future restoration scenarios and estimate historical fish communities. Much life-history data in the model had to be estimated because no data were available. We intend to use previously collected specimens and new collections to study recruitment, age, and growth in representative species of large- and small-bodied fishes. The data will improve the fish model, and explain patterns of community change observed in the long-term fish database, giving us more confidence in the tools used to restore this internationally recognized ecosystem.

Project objectives and strategy: In the Everglades and Big Cypress wetlands, natural environmental conditions regularly vary on seasonal, annual, or multi-annual time-scales, to which the wetland fishes respond by shifts in relative abundance and standing stocks (Roman et al. 1994; Trexier et al. 1996). Human activities have affected the natural variability by altering the seasonality and areal extent of flooding in the wetlands, by drainage, or by over-inundation (Gunderson and Loftus 1993). The human-induced changes have resulted in loss of diversity, changes in composition and abundance, and possible alterations in energy-flow pathways (Loftus et al. 1990). Although these changes in population size and community structure are ultimately related to marsh hydrology, proximate factors that explain some of this variation probably include inherent reproductive adaptations to ambient conditions, such as the seasonality of recruitment, the age/size at first reproduction, growth rates, and other important life-history parameters.

Fishes are essential to the successful functioning of wetlands in southern Florida through their roles as prey and predators. Any changes that alter the population sizes, community composition, or availability of aquatic animals will affect all facets of the ecology of these wetlands. Therefore fishes have been recognized by the multi-agency groups responsible for guiding the Everglades restoration process as a key indicator group by which to measure restoration success. Communities of small-bodied fishes have been studied in EVER since 1977 by using throw traps in spikerush marshes at many Everglades sites (Loftus and Eklund 1994, Trexler et al. 1996). The data analyses allow evaluation of seasonal and long-term dynamics, shifts in relative abundance and size-structure, and produce correlations of fish abundance to water depth, hydroperiod, and plant community structure.

Despite an increasing emphasis on fish studies, important gaps in baseline knowledge remain. Life-history parameters of important fish species remain to be studied at sites along hydroperiod gradients. Some life-history characteristics are known to be rather plastic in response to the environment. We intend to study the effect of hydroperiod on recruitment; size/age structure, growth, and fecundity, which, in turn, determine fish population dynamics. At present, data on fish reproduction, age and growth, and other life-history characteristics are confined to a few species from a limited area of long-hydroperiod marsh in central Shark River Slough. As we continue the analysis and synthesis of data from the long-term fish collections, life-history information will help explain patterns of fluctuations in the time series. Accurate life-history data are also very important in building credible simulation models like ATLSS. Without empirical life-history data from a range of environments, the model will be simplistic and inadequate.

STUDY DESIGN - In this study we propose to collect information for common large- and small-bodied species by taking advantage of existing or newly funded fish studies in south Florida. These include the throw-trap program for small-fish monitoring, and a new electrofishing study of larger native and introduced species in canals. From the electrofishing study, Dr. Nico and graduate student will focus on the collection of the following species:

Non-indigenous species: Spotted tilapia (Tilapia mariae) - an abundant and widespread species;

Native species:
Florida gar (Lepisosteus platyrhincus) ÷ abundant predator on other fish and crustaceans;
Yellow bullhead (Ameiurus natalis) ÷ most abundant catfish, and also a predator;
Warmouth (Lepomis gulosus) - Common sunfish that preys o1i-vrayfish, shrimp, and fish;
Spotted sunfish (Lepomis punctatus) ÷ Abundant sunfish that feeds on invertebrates.

Samples of these species from canal habitats, where they are very abundant at drier times of year, will be preserved in formalin for gonadal examination, with another sample saved in ethanol to avoid damage to the calcium-rich hard tissues used for aging. We anticipate that it will be more difficult to collect adequate sample sizes of large fish at high-water times when they disperse from canals into wetlands. Dr. Nico plans to put in more effort at those times, and to supplement his collections with previously preserved specimens in our collections. Collections will be made quarterly throughout the year.

For the small-bodied species, Dr. Trexler and I plan to concentrate on the following species that inhabit marsh habitats, and about which little life-history information is known. Age and growth information has been collected for some of the species (Haake and Dean 1983), but reproductive characteristics require study. These species, in total, represent the most numerous species in the marshes:

Age and Growth data ÷ Sailfin molly (Poecilia latipinna); Flagfish (Jordanella floridae); and Spotted sunfish (Information specifically on marsh populations of spotted sunfish is needed).

Reproduction/phenology ÷ Least killifish (Heterandria formosa); Bluefin killifish (Lucania goodei); Golden topminnow (Fundulus chrysotus); Eastern mosquitofish (Gambusia hoibrooki); Sailfin molly; and Flagfish.

We plan to use existing archived collections of fishes from our extensive spatial and temporal marsh studies for reproductive analyses of fecundity, size of maturity, seasonality of reproduction, and sex ratios. A companion effort to sample larval fish in the wetlands will provide data for recruitment patterns and effort. The preserved collections will be supplemented during routine sampling five times per year by fresh collections of fishes, which will be frozen or preserved in alcohol for otolith (earbone) analysis. The proposed work will include counts of daily rings on otoliths, and size-frequency analyses to create an age-at-size table for each species, and to estimate growth in different seasons and along the hydroperiod gradient. These studies will allow us to construct life-tables for the species under different conditions in the Everglades. Data from several years are needed because each year in the Everglades can be idiosyncratic. We plan to collect field data from at least two years, and supplement those data with previously collected samples to expand the temporal scope of the study.

Potential impacts and major products: We are using a system of empirical data collection and simulation
modeling to apply information on fish-community patterns in guiding the restoration process. We are describing the functional responses of present-day community density and standing stock to environmental conditions across the landscape. The empirical data also help to build simulation models with which to estimate fish-community parameters under modeled pre-management conditions, allowing us to establish restoration targets. By applying the fish models to restoration alternatives and predicting fish-community responses, we can choose the alternatives that result in biotic characteristics that approximate historical conditions. The iterative process of evaluating and testing the fish-community simulation model in ATLSS also helps identify important data gaps to guide future research. One of the most obvious gaps is the absence of good life-history data, critical to model performance, for most of the fishes. The benefits to restoration would arise by having more confidence in improved tools, like the ATLSS models, that are used to evaluate alternatives for ecological effects of the Central and Southern Florida Project restudy, C-111 Project, and Modified Water Deliveries Plan to Shark Slough.

In addition to the application of the life-history data to modeling and to interpretation of the data time-series, these data represent new information about the adaptations of many of these species in wetland habitats that form the southern extent of their geographic ranges. These also represent the first life-history data for some of the most abundant introduced species in Florida, and may identify vulnerable life stages for controlling these species. The publications resulting from this work will be scientifically significant for those reasons.

Literature Cited

Gunderson, L. H. and W. F. Loftus. 1993. The Everglades. Pages 199-255 in W. H. Martin, S. G. Boyce, and E. G. Echternacht (Editors). Biodiversity of the southeastern United States: Lowland terrestrial communities. John Wiley & Sons, New York.

Haake, P. W. and J. M. Dean. 1983. Age and growth of four Everglades fishes using otolith techniques. Report SFRC-83/03, South Florida Research Center, Everglades N. P. , Homestead, FL. 68 pages.

Loftus, W. F., J. D. Chapman, and R. Conrow. 1990. Hydroperiod effects on Everglades marsh food webs, with relation to marsh restoration efforts, pp. 1-22 IN G. Larson and M. Soukup (Editors). Fisheries and Coastal Wetlands Research. Proceedings of the 1986 Conference on Science in National Parks, Volume 6.

Loftus, W. F. and A. M. Eklund. 1994. Long-term dynamics of an Everglades fish community. Chapter 19, pp. 461-483 IN S. Davis and J.C. Ogden (Editors). Everglades: the System and its Restoration. St. Lucie Press, Delray Beach, Florida.

Roman, C. T., N. G. Aumen, J. C. Trexler, R. J. Fennema, W. F. Loftus, and M. A. Soukup. 1994. Hurricane Andrewâs impact on freshwater resources. Bioscience 44:247-255.

Trexler, J. C.., W. F. Loftus, and O. L Bass. 1996. Documenting the effects of Hurricane Andrew on Everglades aquatic communities, Part III, pp. 6-136 IN J. C. Trexler, L Richardson, and K. Spitze. Effects of Hurricane Andrew on the structure and function of Everglades aquatic communities. Final Report CA5280-3-9014 to Everglades National Park, Homestead, FL

Collaborators, clients (Names, affiliations, and roles of internal and external users of information generated by project):

Collaborators -
Dr. Leo Nico, USGS-BRD, FCSC, Gainesville, Florida
Dr. Joel Trexier, Florida International University, Miami, Florida

Clients -
Other DOI agencies, in particular the National Park Service.
University of Tennessee, which is modifying the ATLSS models
Army Corps of Engineers, using ATLSS in restoration evaluations


OVERALL - Before these data can be integrated into the ATLSS model, we must perform several small-scale pilot studies to verify the methods used to generate the age and growth, and reproduction data. In particular, in aging studies, it is important to verify that the annuli seen on the hard tissues that are used to estimate the fishâs age, are laid down on the interval assumed, either daily or yearly. This is verifiable by either spawning and rearing known-aged specimens and then counting the rings they deposit, or by using a chemical marker to etch the hard tissue, then rearing the fish in captivity for a time to relate the time since marking to the time in captivity. We also must do a pilot study to determine the best methods for estimating the reproductive parameters, including how to sample the gonads for reproductive state, and how to estimate fecundity in fractional spawners.

INTEGRATION - Clean data sets will be transferred to the modelers that will use these data to improve mod performance.

PRODUCTS - A publication on the reproduction and phenology of large-bodied fishes associated with canals, and the same for the small-bodied marsh fishes, in comparison to the patterns reported for these species in other SE US waters and to patterns identified for fishes that inhabit other seasonal wetlands.

Publications that report the age and growth data for the large- and small-bodied fishes in canals and marshes, with relation to habitat seasonality.
  Pilot Studies 99 All
  Reproduction ÷ gonadal exam/field observ.
   Large species
   Small species
99-01 Nico
  Age and growth ÷ otolith/size frequency data
   Large species - quarterly
   Small species - 5X per year
99-01 Nico
  Publications/Fact sheets 00-02 All
  Deliverables - See Above    
  Outreach - Fact sheets, presentations at scientific meetings, workshop with modelers


I have performed aquatic ecology investigations in South Florida for 22 years, mostly in Everglades habitats. I have managed a contract study that estimated the age and growth of four small marsh fishes in the Everglades, and was trained in the method that was proven to work in this region. I have also supervised two preliminary studies of reproductive characteristics and phenology in the Everglades. Those efforts have provided Some background in methods development useful in this proposed study.


Names and expertise (e.g. carbonate petrology) of key project staff (list by fiscal year for duration of project):

All Fiscal Years:
William F. Loftus, USGS-BRD ÷ Wetland ecology of fishes and invertebrates
Leo Nico, USGS-BRD ÷ Biology of fishes, especially introduced species
Joel Trexler, FLU ÷ Ecology and life history of fishes



Major equipment/facility needs (list by fiscal year for duration of project):

Airboat: FY99-O1
Electrofishing Units: FY99-O1
Biology Labs with microscopes: FY99-O1
Computers/Software: FY99-O 1

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